Matt Williams, Author at Universe Today

July 5, 2015November 28, 2016 by Matt Williams

Who Was Nicolaus Copernicus?

Astronomer Copernicus, or Conversations with God, by Matejko. Credit: frombork.art.pl/pl/

When it comes to understanding our place in the universe, few scientists have had more of an impact than Nicolaus Copernicus. The creator of the Copernican Model of the universe (aka. heliocentrism), his discovery that the Earth and other planets revolved the Sun triggered an intellectual revolution that would have far-reaching consequences.

In addition to playing a major part in the Scientific Revolution of the 17th and 18th centuries, his ideas changed the way people looked at the heavens, the planets, and would have a profound influence over men like Johannes Kepler, Galileo Galilei, Sir Isaac Newton and many others. In short, the “Copernican Revolution” helped to usher in the era of modern science.

Copernicus’ Early Life:

Copernicus was born on February 19th, 1473 in the city of Torun (Thorn) in the Crown of the Kingdom of Poland. The youngest of four children to a well-to-do merchant family, Copernicus and his siblings were raised in the Catholic faith and had many strong ties to the Church.

His older brother Andreas would go on to become an Augustinian canon, while his sister, Barbara, became a Benedictine nun and (in her final years) the prioress of a convent. Only his sister Katharina ever married and had children, which Copernicus looked after until the day he died. Copernicus himself never married or had any children of his own.

*Nicolaus Copernicus portrait from Town Hall in Torun (Thorn), 1580. Credit: frombork.art.pl*

Born in a predominately Germanic city and province, Copernicus acquired fluency in both German and Polish at a young age, and would go on to learn Greek and Italian during the course of his education. Given that it was the language of academia in his time, as well as the Catholic Church and the Polish royal court, Copernicus also became fluent in Latin, which the majority of his surviving works are written in.

Copernicus’ Education:

In 1483, Copernicus’ father (whom he was named after) died, whereupon his maternal uncle, Lucas Watzenrode the Younger, began to oversee his education and career. Given the connections he maintained with Poland’s leading intellectual figures, Watzenrode would ensure that Copernicus had great deal of exposure to some of the intellectual figures of his time.

Although little information on his early childhood is available, Copernicus’ biographers believe that his uncle sent him to St. John’ School in Torun, where he himself had been a master. Later, it is believed that he attended the Cathedral School at Wloclawek (located 60 km south-east Torun on the Vistula River), which prepared pupils for entrance to the University of Krakow – Watzenrode’s own Alma mater.

In 1491, Copernicus began his studies in the Department of Arts at the University of Krakow. However, he quickly became fascinated by astronomy, thanks to his exposure to many contemporary philosophers who taught or were associated with the Krakow School of Mathematics and Astrology, which was in its heyday at the time.

*A comparison of the geocentric and heliocentric models of the universe. Credit: history.ucsb.edu*

Copernicus’ studies provided him with a thorough grounding in mathematical-astronomical knowledge, as well as the philosophy and natural-science writings of Aristotle, Euclid, and various humanist writers. It was while at Krakow that Copernicus began collecting a large library on astronomy, and where he began his analysis of the logical contradictions in the two most popular systems of astronomy.

These models – Aristotle’s theory of homocentric spheres, and Ptolemy’s mechanism of eccentrics and epicycles – were both geocentric in nature. Consistent with classical astronomy and physics, they espoused that the Earth was at the center of the universe, and that the Sun, the Moon, the other planets, and the stars all revolved around it.

Before earning a degree, Copernicus left Krakow (ca. 1495) to travel to the court of his uncle Watzenrode in Warmia, a province in northern Poland. Having been elevated to the position of Prince-Bishop of Warmia in 1489, his uncle sought to place Copernicus in the Warmia canonry. However, Copernicus’ installation was delayed, which prompted his uncle to send him and his brother to study in Italy to further their ecclesiastic careers.

In 1497, Copernicus arrived in Bologna and began studying at the Bologna University of Jurists’. While there, he studied canon law, but devoted himself primarily to the study of the humanities and astronomy. It was also while at Bologna that he met the famous astronomer Domenico Maria Novara da Ferrara and became his disciple and assistant.

The Geocentric View of the Solar System — *An illustration of the Ptolemaic geocentric system by Portuguese cosmographer and cartographer Bartolomeu Velho, 1568. Credit: bnf.fr*

Over time, Copernicus’ began to feel a growing sense of doubt towards the Aristotelian and Ptolemaic models of the universe. These included the problematic explanations arising from the inconsistent motion of the planets (i.e. retrograde motion, equants, deferents and epicycles), and the fact that Mars and Jupiter appeared to be larger in the night sky at certain times than at others.

Hoping to resolve this, Copernicus used his time at the university to study Greek and Latin authors (i.e. Pythagoras, Cicero, Pliny the Elder, Plutarch, Heraclides and Plato) as well as the fragments of historic information the university had on ancient astronomical, cosmological and calendar systems – which included other (predominantly Greek and Arab) heliocentric theories.

In 1501, Copernicus moved to Padua, ostensibly to study medicine as part of his ecclesiastical career. Just as he had done at Bologna, Copernicus carried out his appointed studies, but remained committed to his own astronomical research. Between 1501 and 1503, he continued to study ancient Greek texts; and it is believed that it was at this time that his ideas for a new system of astronomy – whereby the Earth itself moved – finally crystallized.

The Copernican Model (aka. Heliocentrism):

In 1503, having finally earned his doctorate in canon law, Copernicus returned to Warmia where he would spend the remaining 40 years of his life. By 1514, he began making his Commentariolus (“Little Commentary”) available for his friends to read. This forty-page manuscript described his ideas about the heliocentric hypothesis, which was based on seven general principles.

These seven principles stated that: Celestial bodies do not all revolve around a single point; the center of Earth is the center of the lunar sphere—the orbit of the moon around Earth; all the spheres rotate around the Sun, which is near the center of the Universe; the distance between Earth and the Sun is an insignificant fraction of the distance from Earth and Sun to the stars, so parallax is not observed in the stars; the stars are immovable – their apparent daily motion is caused by the daily rotation of Earth; Earth is moved in a sphere around the Sun, causing the apparent annual migration of the Sun; Earth has more than one motion; and Earth’s orbital motion around the Sun causes the seeming reverse in direction of the motions of the planets.

Heliocentric Model — *Andreas Cellarius’s illustration of the Copernican system, from the Harmonia Macrocosmica (1708). Credit: Public Domain*

Thereafter he continued gathering data for a more detailed work, and by 1532, he had come close to completing the manuscript of his magnum opus – De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres). In it, he advanced his seven major arguments, but in more detailed form and with detailed computations to back them up.

However, due to fears that the publication of his theories would lead to condemnation from the church (as well as, perhaps, worries that his theory presented some scientific flaws) he withheld his research until a year before he died. It was only in 1542, when he was near death, that he sent his treatise to Nuremberg to be published.

Copernicus’ Death:

Towards the end of 1542, Copernicus suffered from a brain hemorrhage or stroke which left him paralyzed. On May 24th, 1543, he died at the age of 70 and was reportedly buried in the Frombork Cathedral in Frombork, Poland. It is said that on the day of his death, May 24th 1543 at the age of 70, he was presented with an advance copy of his book, which he smiled upon before passing away.

In 2005, an archaeological team conducted a scan of the floor of Frombork Cathedral, declaring that they had found Copernicus’ remains. Afterwards, a forensic expert from the Polish Police Central Forensic Laboratory used the unearthed skull to reconstruct a face that closely resembled Copernicus’ features. The expert also determined that the skull belonged to a man who had died around age 70 – Copernicus’ age at the time of his death.

These findings were backed up in 2008 when a comparative DNA analysis was made from both the remains and two hairs found in a book Copernicus was known to have owned (Calendarium Romanum Magnum, by Johannes Stoeffler). The DNA results were a match, proving that Copernicus’ body had indeed been found.

Copernicus' 2010 grave in Frombork Cathedral, acknowledging him as the father of heiocentirsm.Credit: — *Copernicus’ 2010 grave in Frombork Cathedral, acknowledging him as a church canon and the father of heliocentricism. Credit: Wikipedia/Holger Weinandt*

On May 22nd, 2010, Copernicus was given a second funeral in a Mass led by Józef Kowalczyk, the former papal nuncio to Poland and newly named Primate of Poland. Copernicus’ remains were reburied in the same spot in Frombork Cathedral, and a black granite tombstone (shown above) now identifies him as the founder of the heliocentric theory and also a church canon. The tombstone bears a representation of Copernicus’ model of the solar system – a golden sun encircled by six of the planets.

Copernicus’ Legacy:

Despite his fears about his arguments producing scorn and controversy, the publication of his theories resulted in only mild condemnation from religious authorities. Over time, many religious scholars tried to argue against his model, using a combination of Biblical canon, Aristotelian philosophy, Ptolemaic astronomy, and then-accepted notions of physics to discredit the idea that the Earth itself would be capable of motion.

However, within a few generation’s time, Copernicus’ theory became more widespread and accepted, and gained many influential defenders in the meantime. These included Galileo Galilei (1564-1642), who’s investigations of the heavens using the telescope allowed him to resolve what were seen at the time as flaws in the heliocentric model.

These included the relative changes in the appearances of Mars and Jupiter when they are in opposition vs. conjunction to the Earth. Whereas they appear larger to the naked eye than Copernicus’ model suggested they should, Galileo proved that this is an illusion caused by the behavior of light at a distance, and can be resolved with a telescope.

1973 Federal Republic of Germany 5-mark silver coin commemorating 500th anniversary of Copernicus' birth. Credit: Wikipedia/Berlin-George — *1973 Federal Republic of Germany 5-mark silver coin commemorating 500th anniversary of Copernicus’ birth. Credit: Wikipedia/Berlin-George*

Through the use of the telescope, Galileo also discovered moons orbiting Jupiter, Sunspots, and the imperfections on the Moon’s surface, all of which helped to undermine the notion that the planets were perfect orbs, rather than planets similar to Earth. While Galileo’s advocacy of Copernicus’ theories resulted in his house arrest, others soon followed.

German mathematician and astronomer Johannes Kepler (1571-1630) also helped to refine the heliocentric model with his introduction of elliptical orbits. Prior to this, the heliocentric model still made use of circular orbits, which did not explain why planets orbited the Sun at different speeds at different times. By showing how the planet’s sped up while at certain points in their orbits, and slowed down in others, Kepler resolved this.

In addition, Copernicus’ theory about the Earth being capable of motion would go on to inspire a rethinking of the entire field of physics. Whereas previous ideas of motion depended on an outside force to instigate and maintain it (i.e. wind pushing a sail) Copernicus’ theories helped to inspire the concepts of gravity and inertia. These ideas would be articulated by Sir Isaac Newton, who’s Principia formed the basis of modern physics and astronomy.

Today, Copernicus is honored (along with Johannes Kepler) by the liturgical calendar of the Episcopal Church (USA) with a feast day on May 23rd. In 2009, the discoverers of chemical element 112 (which had previously been named ununbium) proposed that the International Union of Pure and Applied Chemistry rename it copernicum (Cn) – which they did in 2011.

Crater Copernicus on the Moon. Mosaic of photos by Lunar Reconnaissance Orbiter, . Credit: NASA/LRO — *Mosaic image of the Copernicus Crater on the Moon, taken by the Lunar Reconnaissance Orbiter, . Credit: NASA/LRO*

In 1973, on the 500th anniversary of his birthday, the Federal Republic of Germany (aka. West Germany) issued a 5 Mark silver coin (shown above) that bore Copernicus’ name and a representation of the heliocentric universe on one side.

In August of 1972, the Copernicus – an Orbiting Astronomical Observatory created by NASA and the UK’s Science Research Council – was launched to conduct space-based observations. Originally designated OAO-3, the satellite was renamed in 1973 in time for the 500th anniversary of Copernicus’ birth. Operating until February of 1981, Copernicus proved to be the most successful of the OAO missions, providing extensive X-ray and ultraviolet information on stars and discovering several long-period pulsars.

Two craters, one located on the Moon, the other on Mars, are named in Copernicus’ honor. The European Commission and the European Space Agency (ESA) is currently conducting the Copernicus Program. Formerly known as Global Monitoring for Environment and Security (GMES), this program aims at achieving an autonomous, multi-level operational Earth observatory.

On February 19th, 2013, the world celebrated the 540th anniversary of Copernicus’ birthday. Even now, almost five and a half centuries later, he is considered one of the greatest astronomers and scientific minds that ever lived. In addition to revolutionizing the fields of physics, astronomy, and our very concept of the laws of motion, the tradition of modern science itself owes a great debt to this noble scholar who placed the truth above all else.

Universe Today has many interesting articles on ancient astronomy, such as What is the Difference Between the Geocentric and Heliocentric Models of the Solar System.

For more information, you should check out Nicolaus Copernicus, the biography of Nicolaus Copernicus, and Planetary Motion: The History of an Idea That Launched the Scientific Revolution.

Astronomy Cast has an episode on Episode 338: Copernicus.

Sources:

July 3, 2015November 18, 2017 by Matt Williams

Uranus’ Moon Titania

Voyager 2's highest-resolution image of Titania shows moderately cratered plains, enormous rifts and long scarps. Near the bottom, a region of smoother plains including the crater Ursula is split by the graben Belmont Chasma. Credit: NASA

Thanks to the Voyager missions, which passed through the outer Solar system in the late 1970s and early 1980s, scientists were able to get the first close look at Uranus and its system of moons. Like all of the Solar Systems’ gas giants, Uranus has many fascinating satellites. In fact, astronomers can now account for 27 moons in orbit around the teal-colored giant.

Of these, none are greater in size, mass, or surface area than Titania, which was appropriately named. As one of the first moon’s to be discovered around Uranus, this heavily cratered and scarred moon takes it name from the fictional Queen of the Fairies in Shakespeare’s A Midsummer Night’s Dream.

Discovery and Naming:

Titania was discovered by William Herschel on January 11th, 1787, the English astronomer who had discovered Uranus in 1781. The discovery was also made on the same day that he discovered Oberon, Uranus’ second-largest moon. Although Herschel reported observing four other moons at the time, the Royal Astronomical Society would later determine that this claim was spurious.

It would be almost five decades after Titania and Oberon was discovered that an astronomer other than Herschel would observe them. In addition, Titania would be referred to as “the first satellite of Uranus” for many years – or by the designation Uranus I, which was given to it by William Lassell in 1848.

A montage of Uranus's moons. Image credit: NASA — *A montage of Uranus’s moons. Image credit: NASA*

By 1851, Lassell began to number all four known satellites in order of their distance from the planet by Roman numerals, at which point Titania’s designation became Uranus III. By 1852, Herschel’s son John, and at the behest of Lassell himself, suggested the moon’s name be changed to Titania, the Queen of the Fairies in A Midsummer Night’s Dream. This was consistent with all of Uranus’ satellites, which were given names from the works of William Shakespeare and Alexander Pope.

Size, Mass and Orbit:

With a diameter of 1,578 kilometers, a surface area of 7,820,000 km² and a mass of 3.527±0.09 × 10²¹ kg, Titania is the largest of Uranus’ moons and the eighth largest moon in the Solar System. At a distance of about 436,000 km (271,000 mi), Titania is also the second farthest from the planet of the five major moons.

Titania’s moon also has a small eccentricity and is inclined very little relative to the equator of Uranus. It’s orbital period, which is 8.7 days, is also coincident with it’s rotational period. This means that Titania is a synchronous (or tidally-locked) satellite, with one face always pointing towards Uranus at all times.

Because Uranus orbits the Sun on its side, and its moons orbit the planet’s equatorial plane, they are all subject to an extreme seasonal cycle, where the northern and southern poles experience 42 years of either complete darkness or complete sunlight.

*Uranus and its five major moons, with Titania being the farthest left. Credit: space.com*

Composition:

Scientists believe Titania is composed of equal parts rock (which may include carbonaceous materials and organic compounds) and ice. This is supported by examinations that indicate that Titania has an unusually high-density for a Uranian satellite (1.71 g/cm³). The presence of water ice is supported by infrared spectroscopic observations made in 2001–2005, which have revealed crystalline water ice on the surface of the moon.

It is also believed that Titania is differentiated into a rocky core surrounded by an icy mantle. If true, this would mean that the core’s radius is approx. 520 km (320 mi), which would mean the core accounts for 66% of the radius of the moon, and 58% of its mass.

As with Uranus’ other major moons, the current state of the icy mantle is unknown. However, if the ice contains enough ammonia or other antifreeze, Titania may have a liquid ocean layer at the core-mantle boundary. The thickness of this ocean, if it exists, is up to 50 km (31 mi) and its temperature is around 190 K.

Naturally, it is unlikely that such an ocean could support life. But assuming this ocean supports hydrothermal vents on its floor, it is possible life could exist in small patches close to the core. However, the internal structure of Oberon depends heavily on its thermal history, which is poorly known at present.

Voyager 2:

The only direct observations made of Titania were conducted by the Voyager 2 space probe, which photographed the moon during its flyby of Uranus in January 1986. These images covered about 40% of the surface, but only 24% was photographed with the precision required for geological mapping.

Voyager’s flyby of Titania coincided with the southern hemisphere’s summer solstice, when nearly the entire northern hemisphere was unilluminated. As with the other major moon’s of Uranus, this prevented the surface from being mapped in any detail. No other spacecraft has visited the Uranian system or Titania before or since, and no mission is planned in the foreseeable future.

Interesting Facts:

Titania is intermediate in terms of brightness, occupying a middle spot between the dark moons of Oberon and Umbriel and the bright moons of Ariel and Miranda. It’s surface is generally red in color (less so than Oberon), except where fresh impact have taken place, which have left the surface blue in color. The surface of Titania is less heavily cratered than the surface of either Oberon or Umbriel, suggesting that its surface is much younger.

Like all of Uranus’ major moons, it’s geology is influenced by a combination of impact craters and endogenic resurfacing. Whereas the former acted over the moon’s entire history and influenced all its surfaces, the latter processes were mainly active following the moon’s formation and resulted in a smoothing out of its features – hence the low number of present-day impact craters.

Overall, scientists have recognized three classes of geological feature on Titania. These include craters, faults (or scarps) and what are known as grabens (sometimes called canyons). Titania’s craters range in diameter from a few kilometers to 326 kilometers – in the case of the largest known crater, Gertrude. Titania’s surface is also intersected by a system of enormous faults (scarps); and in some places, two parallel scarps mark depressions in the satellite’s crust, forming grabens (aka. canyons).

The grabens on Titania range in diameter from 20 to 50 kilometers (12–31 mi) and in a relief (i.e. depth) from 2 to 5 km. The most prominent graben on Titania is the Messina Chasma, which runs for about 1,500 kilometers (930 mi) from the equator almost to the south pole. The grabens are probably the youngest geological features on Titania, since they cut through all craters and even the smooth plains.

Like Oberon, the surface features on Titania have been named after characters in works by Shakespeare, with all of the physical features are named after female characters. For instance, the crater Gertrude is named after Hamlet’s mother, while other craters – Ursula, Jessica, and Imogen – are named after characters from Much Ado About Nothing, The Merchant of Venice, and Cymebline, respectively.

Interestingly, the presence of carbon dioxide on the surface suggests that Titania may also have a tenuous seasonal atmosphere of CO², much like that of the Jovian moon Callisto. Other gases, like nitrogen or methane, are unlikely to be present, because Titania’s weak gravity could not prevent them from escaping into space.

Like all of Uranus’ moons, much remains to be discovered about this most-massive of her satellites. In the coming years, one can only hope that NASA, the ESA, or other space agencies decide that another Voyager-like mission is need to the outer Solar System. Until such time, Uranus and the many moons that orbit it will continue to keep secrets from us.

We have written many articles on Titania here at Universe Today. Here’s How Many Moons Does Uranus Have?, Uranus’ Moon Oberon and Uranus’ Moon Umbriel.

For more information, check out Nine Planets page on Titania and NASA’s Solar System Exploration page on Titania.

Astronomy Cast has an episode on the subject. Here’s Episode 172: William Herschel

Sources:

July 1, 2015August 25, 2016 by Matt Williams

What is a Terrestrial Planet?

The terrestrial planets of our Solar System at approximately relative sizes. From left, Mercury, Venus, Earth and Mars. Credit: Lunar and Planetary Institute

In studying our Solar System over the course of many centuries, astronomers learned a great deal about the types of planets that exist in our universe. This knowledge has since expanded thanks to the discovery of extrasolar planets, many of which are similar to what we have observed here at home.

For example, while hundreds of gas giants of varying size have been detected (which are easier to detect because of their size), numerous planets have also been spotted that are similar to Earth – aka. “Earth-like”. These are what is known as terrestrial planets, a designation which says a lot about a planet how it came to be.

Definition:

Also known as a telluric or rocky planet, a terrestrial planet is a celestial body that is composed primarily of silicate rocks or metals and has a solid surface. This distinguishes them from gas giants, which are primarily composed of gases like hydrogen and helium, water, and some heavier elements in various states.

The term terrestrial planet is derived from the Latin “Terra” (i.e. Earth). Terrestrial planets are therefore those that are “Earth-like”, meaning they are similar in structure and composition to planet Earth.

Earth-like planets. Image Credit: JPL — *Artist’s concept for the range of Earth-like extrasolar planets that have been discovered in recent years. Credit: NASA/JPL*

Composition and Characteristics:

All terrestrial planets have approximately the same type of structure: a central metallic core composed of mostly iron, with a surrounding silicate mantle. Such planets have common surface features, which include canyons, craters, mountains, volcanoes, and other similar structures, depending on the presence of water and tectonic activity.

Terrestrial planets also have secondary atmospheres, which are generated through volcanism or comet impacts. This also differentiates them from gas giants, where the planetary atmospheres are primary and were captured directly from the original solar nebula.

Terrestrial planets are also known for having few or no moons. Venus and Mercury have no moons, while Earth has only the one (the Moon). Mars has two satellites, Phobos and Deimos, but these are more akin to large asteroids than actual moons. Unlike the gas giants, terrestrial planets also have no planetary ring systems.

The Earth's layers. Credit: discovermagazine.com — *The Earth’s interior structure, shown here as consisting of multiple “layers”. Credit: discovermagazine.com*

Solar Terrestrial Planets:

All those planets found within the Inner Solar System – Mercury, Venus, Earth and Mars – are examples of terrestrial planets. Each are composed primarily of silicate rock and metal, which is differentiated between a dense, metallic core and a silicate mantle. The Moon is similar, but has a much smaller iron core.

Io and Europa are also satellites that have internal structures similar to that of terrestrial planets. In the case of the former, models of the moon’s composition suggest that the mantle is composed primarily of silicate rock and iron, which surrounds a core of iron and iron sulphide. Europa, on the other hand, is believed to have an iron core that is surrounded by an outer layer of water.

Dwarf planets, like Ceres and Pluto, and other large asteroids are similar to terrestrial planets in the fact that they do have a solid surface. However, they differ in that they are, on average, composed of more icy materials than rock.

Extrasolar Terrestrial Planets:

Most of the planets detected outside of the Solar System have been gas giants, owing to the fact that they are easier to spot. However, since 2005, hundreds of potentially terrestrial extrasolar planets have been found – mainly by the Kepler space mission. Most of these have been what is known as “super-Earths” (i.e. planets with masses between Earth’s and Neptune’s).

Examples of extrasolar terrestrial planets include Gliese 876 d, a planet that has a mass 7 to 9 times that of Earth. This planet orbits the red dwarf Gliese 876, which is located approximately 15 light years from Earth. The existence of three (or possibly four) terrestrial exoplanets was also confirmed between 2007 and 2010 in the Gliese 581 system, another red dwarf roughly 20 light years from Earth.

The smallest of these, Gliese 581 e, is only about 1.9 Earth masses, but orbits very close to the star. Two others, Gliese 581 c and Gliese 581 d, as well as a proposed fourth planet (Gliese 581 g) are more-massive super-Earths orbiting in or close to the habitable zone of the star. If true, this could mean that these worlds are potentially habitable Earth-like planets.

The first confirmed terrestrial exoplanet, Kepler-10b – a planet with between 3 and 4 Earth masses and located some 460 light years from Earth – was found in 2011 by the Kepler space mission. In that same year, the Kepler Space Observatory team released a list of 1235 extrasolar planet candidates, including six that were “Earth-size” or “super-Earth-size” (i.e. less than 2 Earth radii) and which were located within their stars’ habitable zones.

Since then, Kepler has discovered hundreds of planets ranging from Moon-sized to super-Earths, with many more candidates in this size range. As of January, 2013, 2740 planet candidates have been discovered.

Categories:

Scientists have proposed several categories for classifying terrestrial planets. Silicate planets are the standard type of terrestrial planet seen in the Solar System, which are composed primarily of a silicon-based rocky mantle and a metallic (iron) core.

Iron planets are a theoretical type of terrestrial planet that consists almost entirely of iron and therefore has a greater density and a smaller radius than other terrestrial planets of comparable mass. Planets of this type are believed to form in the high-temperature regions close to a star, and where the protoplanetary disk is rich in iron. Mercury is possible example, which formed close to our Sun and has a metallic core equal to 60–70% of its planetary mass.

Coreless planets are another theoretical type of terrestrial planet, one that consists of silicate rock but has no metallic core. In other words, coreless planets are the opposite of an iron planet. Coreless planets are believed to form farther from the star where volatile oxidizing material is more common. Though the Solar System has no coreless planets, chondrite asteroids and meteorites are common.

And then there are Carbon planets (aka. “diamond planets”), a theoretical class of planets that are composed of a metal core surrounded by primarily carbon-based minerals. Again, the Solar System has no planets that fit this description, but has an abundance of carbonaceous asteroids.

Until recently, everything scientists knew about planets – which included how they form and the different types that exist – came from studying our own Solar System. But with the explosion that has taken place in exoplanet discovery in the past decade, what we know about planets has grown significantly.

For one, we have come to understand that the size and scale of planets is greater than previously thought. What’s more, we’ve seen for the first time that many planets similar to Earth (which could also include being habitable) do in fact exist in other Solar Systems.

Who knows what we will find once we have the option of sending probes and manned missions to other terrestrial planets?

Universe Today has articles on smallest terrestrial exoplanet and gas planets. For the latest information on confirmed extrasolar planets, be sure to check out the Kepler’s Planet Candidates.

For a full list of all confirmed and potential planets, consult the Extrasolar Planet Encyclopaedia.

Astronomy Cast has episodes on the terrestrial planets including Mars, and an interview with Darin Ragozzine, one of the Kepler Space Mission scientists.

June 30, 2015November 7, 2016 by Matt Williams

Who Were the First Men on the Moon?

Bootprint in the lunar regolith left behing by the Apollo 11 crew. Credit: NASA

On July 20th, 1969, history was made when men walked on the Moon for the very first time. The result of almost a decade’s worth of preparation, billions of dollars of investment, strenuous technical development and endless training, the Moon Landing was the high point of the Space Age and the single greatest accomplishment ever made.

Because they were the first men to walk on the Moon, Neil Armstrong and Edwin “Buzz” Aldrin are forever written in history. And since that time, only ten men have had the honor of following in their footsteps. But with plans to return to the Moon, a new generation of lunar explorers is sure to be coming soon. So just who were these twelve men who walked on the Moon?

Prelude to the Moon Landing:

Before the historic Apollo 11 mission and Moon Landing took place, NASA conducted two manned missions to test the Apollo spacecraft and the Saturn V rockets that would be responsible for bringing astronauts to the lunar surface. The Apollo 8 mission – which took place on Dec. 21st, 1968 – would be the first time a spacecraft left Earth orbit, orbited the Moon, and then returned safely to Earth.

During the mission, the three-astronaut crew – Commander Frank Borman, Command Module Pilot James Lovell, and Lunar Module Pilot William Anders – spent three days flying to the Moon, then completed 10 circumlunar orbits in the course of 20 hours before returning to Earth on Dec. 27th.

During one of their lunar orbits, the crew made a Christmas Eve television broadcast where they read the first 10 verses from the Book of Genesis. At the time, the broadcast was the most watched TV program in history, and the crew was named Time magazine’s “Men of the Year” for 1968 upon their return.

On May 18th, 1969, in what was described as a “dress rehearsal” for a lunar landing, the Apollo 10 mission blasted off. This involved testing all the components and procedures that would be used for the sake of the Moon Landing.

The crew – which consisted of Thomas P. Stafford as Commander, John W. Young as the Command Module Pilot, and Eugene A. Cernan as the Lunar Module Pilot – flew to the Moon and passed within 15.6 km (8.4 nautical miles) of the lunar surface before returning home.

Apollo 11:

On July 16th, 1969, at 13:32:00 UTC (9:32:00 a.m. EDT local time) the historic Apollo 11 mission took off from the Kennedy Space Center in Florida. The crew consisted of Neil Armstrong as the Commander, Michael Collins as the Command Module Pilot), and Edwin “Buzz” Aldrin as the Lunar Module Pilot.

Neil Armstrong and Buzz Aldrin plant the US flag on the Lunar Surface during 1st human moonwalk in history 45 years ago on July 20, 1969 during Apollo 1l mission. Credit: NASA — *Neil Armstrong and Buzz Aldrin plant the US flag on the Lunar Surface during the first human moonwalk in history on July 20, 1969. Credit: NASA*

On July 19th at 17:21:50 UTC, Apollo 11 passed behind the Moon and fired its service propulsion engine to enter lunar orbit. On the following day, the Lunar Module Eagle separated from the Command Module Columbia, and Armstrong and Aldrin commenced their Lunar descent.

Taking manual control of the Lunar Module, Armstrong brought them down to a landing spot in the Sea of Tranquility, and then announced their arrival by saying: “Houston, Tranquility Base here. The Eagle has landed.” After conducting post-landing checks and depressurizing the cabin, Armstrong and Aldrin began descending the ladder to the lunar surface.

When he reached the bottom of the ladder, Armstrong said: “I’m going to step off the LEM now” (Lunar Excursion Module). He then turned and set his left boot on the surface of the Moon at 2:56 UTC July 21st, 1969, and spoke the famous words “That’s one small step for [a] man, one giant leap for mankind.”

About 20 minutes after the first step, Aldrin joined Armstrong on the surface, and the two men began conducting the planned surface operations. In so doing, they became the first and second humans to set foot on the Moon.

Apollo 12:

Four months later, on November 14th, 1969, the Apollo 12 mission took off from the Kennedy Space Center. Crewed by Commander Charles “Pete” Conrad, Lunar Module Pilot Alan L. Bean and Command Module Pilot Richard F. Gordon, this mission would be the second time astronauts would walk on the Moon.

Ten days later, the Lunar Module touched down without incident on the southeastern portion of the Ocean of Storms. When Conrad and Bean reached the lunar surface, Bean’s first words were: “Whoopie! Man, that may have been a small one step for Neil, but that’s a long one for me.” In the course of conducting a Extra-Vehicular Activities (EVAs), the two astronauts became the third and fourth men to walk on the Moon.

The crew also brought the first color television camera to film the mission, but transmission was lost after Bean accidentally destroyed the camera by pointing it at the Sun. On one of the two EVAs, the crew visited the Surveyor 3 unmanned probe, which had landed in the Ocean of Storms on April 20th, 1967. The mission ended on November 24th with a successful splashdown.

*Pete Conrad descends from the Lunar Module (LM). Credit: NASA*

Apollo 14:

The Apollo 13 mission was intended to be the third lunar landing; but unfortunately, the explosion of the oxygen tank aboard the Service Module forced the crew to abort the landing. Using the Lunar Module as a “lifeboat”, the crew executed a single loop around the Moon before safely making it back to Earth.

As a result, Apollo 14 would be the third manned mission to the lunar surface, crewed by veteran Alan Shepard (as Commander), Stuart Roosa as Command Module Pilot, and Edgar Mitchell as Lunar Module Pilot. The mission launched on January 31st, 1971 and Shepard and Mitchell made their lunar landing on February 5th in the Fra Mauro formation, which had originally been targeted for the Apollo 13 mission.

During two lunar EVAs, Shepard and Mitchell became the fifth and sixth men to walk on the Moon. They also collected 42 kilograms (93 lb) of Moon rocks and conducted several surface experiments – which including seismic studies. During the 33 hours they spent on the Moon (9½ hours of which were dedicated to EVAs), Shepard famously hit two golf balls on the lunar surface with a makeshift club he had brought from Earth.

*Shepard poses next to the American flag on the Moon during Apollo 14. Credit: NASA*

Apollo 15:

The seventh and eight men to walk on the Moon were David R. Scott, and James B. Irwin – the Commander and Lunar Module Pilot of the Apollo 15 mission. This mission began on July 26th, 1971, and landed near Hadley rille – in an area of the Mare Imbrium called Palus Putredinus (Marsh of Decay) – on August 7th.

The mission was the first time a crew explored the lunar surface using a Lunar Vehicular Rover (LVR), which allowed them to travel farther and faster from the Lunar Module (LM) than was ever before possible. In the course of conducting multiple EVAs, the crew collected 77 kilograms (170 lb) of lunar surface material.

While in orbit, the crew also deployed a sub-satellite, and used it and the Scientific Instrument Module (SIM) to study the lunar surface with a panoramic camera, a gamma-ray spectrometer, a mapping camera, a laser altimeter, and a mass spectrometer. At the time, NASA hailed the mission as “the most successful manned flight ever achieved.”

*Image from Apollo 15, taken by Commander David Scott at the end of EVA-1. Credit: NASA*

Apollo 16:

It was during the Apollo 16 mission – the penultimate manned lunar mission – that the ninth and tenth men were to walk on the Moon. After launching from the Kennedy Space Center on April 16th, 1972, the mission arrived on the lunar surface by April 21st. Over the course of three days, Commander John Young and Lunar Module Pilot Charles Duke conducted three EVAs, totaling 20 hours and 14 minutes on the lunar surface.

The mission was also the second occasion where an LVR was used, and Young and Duke collected 95.8 kilograms (211 lb) of lunar samples for return to Earth, while Command Module Pilot Ken Mattingly orbited in the Command/Service Module (CSM) above to perform observations.

Apollo 16’s landing spot in the highlands was chosen to allow the astronauts to gather geologically older lunar material than the samples obtained in the first four landings. Because of this, samples from the Descartes Cayley Formations disproved a hypothesis that the formations were volcanic in origin. The Apollo 16 crew also released a subsatellite from the Service Module before breaking orbit and returning to Earth, making splashdown by April 27th.

John W. Young on the Moon during Apollo 16 mission. Charles M. Duke Jr. took this picture. The LM Orion is on the left. April 21, 1972. Credit: NASA — *John W. Young standing next to the LM Orion during the Apollo 16 mission, April 21, 1972. Credit: NASA*

Apollo 17:

The last of the Apollo missions, and the final time astronauts would set foot on the moon, began at 12:33 am Eastern Standard Time (EST) on December 7th, 1972. The mission was crewed by Eugene Cernan, Ronald Evans, and Harrison Schmitt – in the roles of Commander, Command Module Pilot and Lunar Module Pilot, respectively.

After reaching the lunar surface, Cernan and Schmitt conducted EVAs and became the eleventh and twelve men to walk on the lunar surface. The mission also broke several records set by previous flights, which included the longest manned lunar landing flight, the longest total lunar surface extravehicular activities, the largest lunar sample return, and the longest time in lunar orbit.

While Evans remained in lunar orbit above in the Command/Service Module (CSM), Cernan and Schmitt spent just over three days on the lunar surface in the Taurus–Littrow valley, conducting three periods of extra-vehicular activity with an LRV, collecting lunar samples and deploying scientific instruments. Cernan, After an approximately 12 day mission, Evans, and Schmitt returned to Earth.

Astronaut Eugene pollo 17 mission, 11 December 1972. Astronaut Eugene A. Cernan, commander, makes a short checkout of the Lunar Roving Vehicle (LRV) — *Astronaut Eugene A. Cernan, commander of the Apollo 17 mission, using a Lunar Roving Vehicle (LRV) for an EVA on December 11th 1972. Credit: NASA*

Apollo 17 remains the most recent manned Moon mission and also the last time humans have traveled beyond low Earth orbit. Until such time as astronauts begin to go to the Moon again (or manned missions are made to Mars) these twelve men – Neil Armstrong, Edwin “Buzz” Aldrin, Charles “Pete” Conrad, Alan L. Bean, Alan Shepard, Edgar Mitchell, David R. Scott, James B. Irwin, John Young, Charles Duke, Eugene Cernan, and Harrison Schmitt – will remain the only human beings to ever walk on a celestial body other than Earth.

Universe today has many interesting articles on the Moon, such as the First Man On The Moon, The Most Famous Astronauts, and articles on Neil Armstrong, Edwin “Buzz” Aldrin and Alan Shepard.

You should also check out the Moon landing and 35th anniversary of the Moon landing.

Astronomy Cast has a three part series on the Moon.

Reference:
NASA Apollo 11

June 28, 2015November 21, 2016 by Matt Williams

What Did Galileo Invent?

Portrait of Galileo Galilei by Giusto Sustermans (1636). Credit: nmm.ac.uk

Galileo is considered one of the greatest astronomers of all time. His discovery of Jupiter’s major moons (Io, Europa, Ganymede and Callisto) revolutionized astronomy and helped speed the acceptance of the Copernican Model of the universe. However, Galileo is also known for the numerous scientific inventions he made during his lifetime.

These included his famous telescope, but also a series of devices that would have a profound impact on surveying, the use of artillery, the development of clocks, and meteorology. Galileo created many of these in order to earn extra money to support his family. But ultimately, they would help cement his reputation as the man who challenged centuries worth of previously-held notions and revolutionized the sciences.

Hydrostatic Balance:

Inspired by the story of Archimedes’ and his “Eureka” moment, Galileo began looking into how jewelers weighed precious metals in air, and then by displacement, to determine their specific gravity. In 1586, at the age of 22, he theorized of a better method, which he described in a treatise entitled La Bilancetta (or “The Little Balance”).

In this tract, he described an accurate balance for weighing things in air and water, in which the part of the arm on which the counter weight was hung was wrapped with metal wire. The amount by which the counterweight had to be moved when weighing in water could then be determined very accurately by counting the number of turns of the wire. In so doing, the proportion of metals like gold to silver in the object could be read off directly.

Galileo's La Billancetta, in which he describes a method for hydrostatic balance. Credit: Museo Galileo — *Galileo’s “La Billancetta”, in which he describes a new method of measuring the specific gravity of precious metals. Credit: Museo Galileo*

Galileo’s Pump:

In 1592, Galileo was appointed professor of mathematics at the University of Padua and made frequent trips to the Arsenal – the inner harbor where Venetian ships were fitted out. The Arsenal had been a place of practical invention and innovation for centuries, and Galileo used the opportunity to study mechanical devices in detail.

In 1593, he was consulted on the placement of oars in galleys and submitted a report in which he treated the oar as a lever and correctly made the water the fulcrum. A year later the Venetian Senate awarded him a patent for a device for raising water that relied on a single horse for operation. This became the basis of modern pumps.

To some, Galileo’s Pump was a merely an improvement on the Archimedes Screw, which was first developed in the third century BCE and patented in the Venetian Republic in 1567. However, there is apparent evidence connecting Galileo’s invention to Archimedes earlier and less sophisticated design.

Pendulum Clock:

During the 16th century, Aristotelian physics was still the predominant way of explaining the behavior of bodies near the Earth. For example, it was believed that heavy bodies sought their natural place or rest – i.e at the center of things. As a result, no means existed to explain the behavior of pendulums, where a heavy body suspended from a rope would swing back and forth and not seek rest in the middle.

Already, Galileo had conducted experiments that demonstrated that heavier bodies did not fall faster than lighter ones – another belief consistent with Aristotelian theory. In addition, he also demonstrated that objects thrown into the air travel in parabolic arcs. Based on this and his fascination with the back and forth motion of a suspended weight, he began to research pendulums in 1588.

In 1602, he explained his observations in a letter to a friend, in which he described the principle of isochronism. According to Galileo, this principle asserted that the time it takes for the pendulum to swing is not linked to the arc of the pendulum, but rather the pendulum’s length. Comparing two pendulum’s of similar length, Galileo demonstrated that they would swing at the same speed, despite being pulled at different lengths.

According to Vincenzo Vivian, one of Galileo’s contemporaries, it was in 1641 while under house arrest that Galileo created a design for a pendulum clock. Unfortunately, being blind at the time, he was unable to complete it before his death in 1642. As a result, Christiaan Huygens’ publication of Horologrium Oscillatorium in 1657 is recognized as the first recorded proposal for a pendulum clock.

The Sector:

The cannon, which was first introduced to Europe in 1325, had become a mainstay of war by Galileo’s time. Having become more sophisticated and mobile, gunners needed instrumentation to help them coordinate and calculate their fire. As such, between 1595 and 1598, Galileo devised and improved a geometric and military compass for use by gunners and surveyors.

Existing gunner’s compasses relied on two arms at right angles and a circular scale with a plumb line to determine elevations. Meanwhile, mathematical compasses, or dividers, developed during this time were designed with various useful scales on their legs. Galileo combined the uses of both instruments, designing a compass or sector that had many useful scales engraved on its legs that could be used for a variety of purposes.

In addition to offering a new and safer way for gunners to elevate their cannons accurately, it also offered a quicker way of computing the amount of gunpowder needed based on the size and material of the cannonball. As a geometric instrument, it enabled the construction of any regular polygon, computation of the area of any polygon or circular sector, and a variety of other calculations.

Galileo’s Thermometer:

During the late 16th century, there existed no practical means for scientists to measure heat and temperature. Attempts to rectify this within the Venetian intelligentsia resulted in the thermoscope, an instrument that built on the idea of the expansion of air due to the presence of heat.

In ca. 1593, Galileo constructed his own version of a thermoscope that relied on the expansion and contraction of air in a bulb to move water in an attached tube. Over time, he and his colleagues worked to develop a numerical scale that would measure the heat based on the expansion of the water inside the tube.

Galileo Galilei's telescope with his handwritten note specifying the magnifying power of the lens, at an exhibition at The Franklin Institute in Philadelphia. Credit: AP Photo/Matt Rourke — *Galileo Galilei’s telescope with his handwritten note specifying the magnifying power of the lens, at an exhibition at The Franklin Institute in Philadelphia. Credit: AP Photo/Matt Rourke*

And while it would take another century before scientists – such as Daniel G. Fahrenheit and Anders Celsius – began developing universal temperature scales that could be used in such instrument, Galileo’s thermoscope was a major breakthrough. In addition to being able to measure heat in air, it also provided quantitative meteorological information for the first time ever.

Galileo’s Telescope:

While Galileo did not invent the telescope, he greatly improved upon them. Over the course of many months during 1609, he unveiled multiple telescope designs that would collectively come to be known as Galilean Telescopes. The first, which he constructed between June and July of 1609, was a three-powered spyglass, which he replaced by August with an eight-powered instrument that he presented to the Venetian Senate.

By the following October or November, he managed to improve upon this with the creation a twenty-powered telescope – the very telescope that he used to observe the Moon, discover the four satellites of Jupiter (thereafter known as the Galilean Moons), discern the phases of Venus, and resolve nebular patches into stars.

These discoveries helped Galileo to advance the Copernican Model, which essentially stated that the Sun (and not the Earth) was the center of the universe (aka. heliocentrism). He would go on to refine his designs further, eventually creating a telescope that could magnify objects by a factor of 30.

Though these telescopes were humble by modern standards, they were a vast improvement over the models that existed during Galileo’s time. The fact that he managed to construct them all himself is yet another reason why they are considered his most impressive inventions.

Because of the instruments he created and the discoveries they helped make, Galileo is rightly recognized as one of the most important figures of the Scientific Revolution. His many theoretical contributions to the fields of mathematics, engineering and physics also challenged Aristotelian theories that had been accepted for centuries.

In short, he was one of just a few people who – through their tireless pursuit of scientific truth – forever changed our understanding of the universe and the fundamental laws that govern it.

Universe Today has articles on Galileo’s telescope and scientists want to exhume Galileo’s body.

For more information, check out the Galileo Project and Galileo the telescope and the Laws of Dynamics.

Astronomy Cast has an episode on choosing and using a telescope and how to build your own.

Source: NASA

June 27, 2015December 23, 2015 by Matt Williams

What are the Signs of the Planets?

The symbols of the eight planets, and Pluto, Credit: insightastrology.net

In our long history of staring up at the stars, human beings have assigned various qualities, names, and symbols for all the objects they have found there. Determined to find patterns in the heavens that might shed light on life here on Earth, many of these designations also ascribed (and were based on) the observable behavior of the celestial bodies.

When it came to assigning signs to the planets, astrologists and astronomers – which were entwined disciplines in the past -made sure that these particular symbols were linked to the planets’ names or their history in some way.

Mercury:
This planet is named after the Roman god who was himself the messenger of the gods, noted for his speed and swiftness. The name was assigned to this body largely because it is the planet closest to the Sun, and which therefore has the fastest rotational period. Hence, the symbol is meant to represent Mercury’s helmet and caduceus – a herald’s staff with snakes and wings intertwined.

Mercury, as imaged by the MESSENGER spacecraft, revealing parts of the never seen by human eyes. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington — *Mercury, as imaged by the MESSENGER spacecraft, which was named after the messenger of the gods because it has the fastest orbit around the Sun. Image Credit: NASA/JHU/Carnegie Institution.*

Venus:
Venus’ symbol has more than one meaning. Not only is it the sign for “female”, but it also represents the goddess Venus’ hand mirror. This representation of femininity makes sense considering Venus was the goddess of love and beauty in the Roman Pantheon. The symbol is also the chemical sign for copper; since copper was used to make mirrors in ancient times.

Earth:
Earth’s sign also has a variety of meanings, although it does not refer to a mythological god. The most popular view is that the circle with a cross in the middle represents the four main compass points. It has also been interpreted as the Globus Cruciger, an old Christian symbol for Christ’s reign on Earth.

This symbol is not just limited to Christianity though, and has been used in various culture around the world. These include, but are not limited to, Norse mythology (where it appears as the Solar or Odin’s Cross), Native American cultures (where it typically represented the four spirits of direction and the four sacred elements), the Celtic Cross, the Greek Cross, and the Egyptian Ankh.

In fact, perhaps owing to the simplicity of the design, cross-shaped incisions have made appearances as petroglyphs in European cult caves dating all the way back to the beginning of the Upper Paleolithic, and throughout prehistory to the Iron Age.

Mars, as photographed with the Mars Global Surveyor, is identified with the Roman god of war. Credit: NASA

Mars:
Mars is named after the Roman god of war, owing perhaps to the planet’s reddish hue, which gives it the color of blood. For this reason, the symbol associated with Mars represents the god of wars’ shield and spear. Additionally, it is the same sign as the one used to represent “male”, and hence is associated with self-assertion, aggression, sexuality, energy, strength, ambition and impulsiveness.

Jupiter:
Jupiter’s sign, which looks like an ornate, oddly shaped “four,” also stands for a number of symbols. It has been said to represent an eagle, which was the Jovian god’s bird. Additionally, the symbol can stand for a “Z,” which is the first letter of Zeus – who was Jupiter’s Greek counterpart.

The line through the symbol is consistent with this, since it would indicate that it was an abbreviation for Zeus’ name. And last, but not least, there is the addition of the swirled line which is believed to represent a lighting bolt – which just happens to Jupiter’s (and Zeus’) weapon of choice.

Saturn:
Like Jupiter, Saturn resembles another recognizable character – this time, it’s an “h.” However, this symbol is actually supposed to represent Saturn’s scythe or sickle, because Saturn is named after the Roman god of agriculture (after the Greek god Cronus, leader of the Titans, who was also depicted as holding a scythe).

Jupiter's Great Red Spot and Ganymede's Shadow. Image Credit: NASA/ESA/A. Simon (Goddard Space Flight Center) — *Jupiter, the largest planet in the Solar System, is appropriately named after the Roman father of the gods. Credit: NASA/ESA/A. Simon (Goddard Space Flight Center)*

Uranus:
The sign for Uranus is a combination of two other signs – Mars’ sign and the symbol of the Sun – because the planet is connected to these two in mythology. Uranus represented heaven in Roman mythology, and this ancient civilization believed that the Sun’s light and Mars’ power ruled the heavens.

Neptune:
Neptune’s sign is linked to the sea god Neptune, who the planet was named after. Appropriately, the symbol represents this planet is in the shape of the sea god’s trident.

Pluto:
Although Pluto was demoted to a dwarf planet in 2006, it still retains its old symbol. Pluto’s sign is a combination of a “P” and a “L,” which are the first two letters in Pluto as well as the initials of Percival Lowell, the astronomer who discovered the planet.

*A full Moon flyby, as seen from Paris, France. Credit and copyright: Sebastien Lebrigand.*

Moon:
The Moon is represented by a crescent shape, which is a clear allusion to how the Moon appears in the night sky more often than not. Since the Moon is also tied to people’s perceptions, moods, and emotional make-up, the symbol has also come to represents the mind’s receptivity.

Sun:
And then there’s the Sun, which is represented by a circle with a dot in the middle. In the case of the Sun, this symbol represents the divine spirit (circle) surrounding the seed of potential, which is a direct association with ancient Sun worship and the central role the Sun gods played in their respective ancient pantheons.

We have many interesting articles on the planets here at Universe Today. For example, here is other articles including symbols of the planets and symbols of the Sun and Moon.

If you are looking for more information try signs of the planets and symbols of the minor planets.

Astronomy Cast has an episode on each planet including Saturn.

June 27, 2015October 24, 2019 by Matt Williams

What Is The Space Age?

A picture of Earth taken by Apollo 11 astronauts. Credit: NASA

With the end of World War II, the Allies and the Soviet Bloc found themselves locked in a state of anatgonism. As they poured over the remains of the Nazi war machine, they discovered incredible advances in rocketry and aerospace engineering, and began scrambling to procure all they could.

For many of the many decades that followed, this state would continue as both sides struggled to make advancements in the field of space exploration ahead of the other. This was what is popularly known as the “Space Age”, an era that was born of the advent of nuclear power, advances in rocketry, and the desire to be the first to put men into space and on the Moon.

Continue reading “What Is The Space Age?”

June 24, 2015December 23, 2015 by Matt Williams

What Is a Tsunami?

11 March 2011: The wave from a tsunami crashes over a street in Miyako City, Japan Credit: REUTERS/Mainichi Shimbun

For people living in oceanfront communities, the prospect of a tsunami is a frightening one. Much like earthquakes, volcanoes, hurricanes and tornadoes, tsunamis are one of the most destructive natural forces on the planet. And much like these other phenomena, they require the right conditions to happen and are more common in some areas of the world than others.

Knowing how and when a tsunami will strike has therefore a subject of great interest for scientists over the ages. But for anyone who has lived in certain parts of the world where “tsunami zones” are common – namely Japan and the South Pacific – it is a matter of survival.

Definition:
Numerous terms are used in the English language to describe large waves created by the displacement of water, with varying degrees of accuracy. The term tsunami, for example, is literally translated from Japanese to mean “harbor wave”. There are only a few other languages that have an equivalent native word, though similar meanings can be found in Indonesia, Sri Lanka, and the Indian Subcontinent.

The term tidal wave has also been used, which is derived from the most common appearance of a tsunami – an extraordinarily high tidal bore. However, in recent years, the term “tidal wave” has fallen out of favor with the scientific community because tsunami actually have nothing to do with tides, which are produced by the gravitational pull of the moon and sun rather than the displacement of water.

*Tsunamis initiate when an earthquake causes the seabed to rupture, which leads to a rapid decrease in sea surface height directly above it. Credit: howitworksdaily.com*

The term seismic sea wave also is used to refer to the phenomenon, due to the fact that the waves most often are generated by seismic activity such as earthquakes. However, like “tsunami,” “seismic sea wave” is not a completely accurate term, as forces other than earthquakes – including underwater landslides, volcanic eruptions, underwater explosions, land or ice slumping into the ocean, meteorite impacts, or even sudden changes in weather – can generate such waves by displacing water.

Causes:
The principal cause of a tsunami is the displacement of a substantial volume of water or perturbation of the sea. This is usually the result of earthquakes, landslides, volcanic eruptions, glacier calvings, or more rarely by meteorites and nuclear tests. The waves formed in this way are then sustained by gravity.

Tectonic earthquakes trigger tsunamis when the sea floor abruptly deforms and vertically displaces the water above. More specifically, a tsunami can be generated when thrust faults associated with convergent or destructive plate boundaries move abruptly and displace water.

Tsunamis have a small amplitude (wave height) offshore, and a very long wavelength (often hundreds of kilometers long), and only grow in height when they reach shallower water. Once there, the wavelength shortens as the wave encounters resistance, thus increasing the amplitude increases and causing the wave to rears up in a massive tidal bore.

In the 1950s, it was discovered that tsunamis larger than what had previously been believed possible could be caused by giant submarine landslides. These rapidly displace large water volumes, as energy transfers to the water at a rate faster than the water can absorb. Their existence was confirmed in 1958, when a giant landslide in Lituya Bay, Alaska, caused the highest wave ever recorded (524 meters/1700 feet).

A village near the coast of Sumatra that was devastated by the 2004 Tsunami. Credit: US Navy — *A village near the coast of Sumatra that was devastated by the Tsunami that struck South-East Asia in 2004. Credit: US Navy/Public Domain*

In general, landslides generate displacements mainly in the shallower parts of the coastline, such as in closed bays and lakes. But an open oceanic landslide large enough to cause a tsunami across an ocean has not yet happened since the advent of modern seismology, and only rarely in human history.

Meteorological phenomena, such tropical cyclones, can generate a storm surge that will cause sea levels to rise, often in coastal regions. These are what is known as meteotsunamis, which are tsunamis triggered by sudden changes in weather. When such tsunamis reach shore, they rear up in shallows and surge laterally, just like earthquake-generated tsunamis.

Tsunamis can also be triggered by external factors, such as meteors or human intervention. For instance, when a meteor of significant strikes a region of the ocean, the resulting impact is enough to displace high volumes of water, thus triggering a tsunami. There has also been much speculation since World War II of how a nuclear detonations have trigger a tsunami, but all attempts at research (especially in the Pacific) have yielded poor results.

Characteristics and Effects:
Tsunamis can travel at well over 800 kilometers per hour (500 mph), but as they approach the coast, wave shoaling compresses the wave and its speed decreases to below 80 kilometers per hour (50 mph). A tsunami in the deep ocean has a much larger wavelength of up to 200 kilometers (120 mi), but diminishes to less than 20 kilometers (12 mi) when it reaches shallow water.

When the tsunami’s wave peak reaches the shore, the resulting temporary rise in sea level is termed run up. Run up is measured in metres above a reference sea level. A large tsunami may feature multiple waves arriving over a period of hours, with significant time between the wave crests.

Tsunamis cause damage by two mechanisms. First, there is the smashing force of a wall of water traveling at high speed, while the second is the destructive power of a large volume of water draining off the land and carrying a large amount of debris with it.

It is often difficult for people to recognize a tsunami in the open ocean because the waves are much smaller further out at sea than they are close to shore. As with earthquakes, several attempts have been made to set up scales of tsunami intensity or magnitude to allow comparison between different events.

Ships try to extinguish a blaze at oil refinery tanks in Ichihara, Chiba Prefecture, which has been burning since Friday's earthquake and tsunami Read more: http://www.dailymail.co.uk/news/article-1366395/Japan-tsunami-earthquake-Rescuers-pick-way-apocalypse-wasteland.html#ixzz3dvVfz0hr Follow us: @MailOnline on Twitter | DailyMail on Facebook Credit: EPA — *Ships try to extinguish a blaze at oil refinery tanks in Ichihara, Chiba Prefecture, after the tsunami that struck in March, 2011. Credit: EPA*

The first scales used routinely to measure the intensity of tsunami were the Sieberg-Ambraseys scale, used in the Mediterranean Sea and the Imamura-Iida intensity scale, used in the Pacific Ocean. This latter scale was modified by Soloviev to become the Soloviev-Imamura tsunami intensity scale, which is used in the global tsunami catalogs compiled by the NGDC/NOAA and the Novosibirsk Tsunami Laboratory as the main parameter for the size of the tsunami.

In 2013, following the intensively studied tsunamis in 2004 and 2011, a new 12 point scale was proposed, known as the Integrated Tsunami Intensity Scale (ITIS-2012). This scale was intended to match as closely as possible to the modified ESI2007 and EMS earthquake intensity scales.

Tsunamis throughout History:
Japan and the Pacific Ocean may have the longest recorded history of tsunamis, but they are an often underestimated hazard in the Mediterranean Sea region and Europe in general. In his History of the Peloponnesian War (426 BCE), Greek historian Thucydides offered what could be considered the first recorded speculation about the causes of tsunamis – where he argued that earthquakes at sea were the reason for them.

An aerial view of tsunami damage in T?hoku. Credit: US Navy — *An aerial view of tsunami damage in Tohoku. Credit: US Navy*

After the tsunami of 365 CE devastated Alexandria, Roman historian Ammianus Marcellinus described the typical sequence of a tsunami. His descriptions included an earthquake and the sudden retreat of the sea, followed by a gigantic wave.

More modern examples include the 1755 Lisbon earthquake and tsunami (which was caused by activity in the Azores–Gibraltar Transform Fault); the 1783 Calabrian earthquakes, which caused several ten thousand deaths; and the 1908 Messina earthquake and tsunami – which caused 123,000 deaths in Sicily and Calabria and is considered one of the most deadly natural disasters in modern European history.

But by far, the 2004 Indian Ocean earthquake and tsunami was the most devastating of its kind in modern times, killing around 230,000 people and laying waste to communities throughout Indonesia, Thailand, and Southern Asia.

In 2010, an earthquake triggered a tsunami which devastated several coastal towns in south-central Chile, damaged the port at Talcahuano and caused 4334 confirmed fatalities. The earthquake also generated a blackout that affected 93 percent of the Chilean population.

In 2011, an earthquake off the Pacific coast of Tohoku led to a tsunami that struck Japan and led to 5,891 deaths, 6,152 injuries, and 2,584 people to be declared missing across twenty prefectures. The tsunami also caused meltdowns at three reactors in the Fukushima Daiichi Nuclear Power Plant complex.

Tsunamis are a force of nature, without a doubt. And knowing when, where, and how severely they will strike is intrinsic to ensuring that we can limit the damage they do cause.

Universe Today has articles on about tsunamis and causes of tsunamis.

For more information, try tsunami and causes of tsunamis.

Astronomy Cast has an episode on Earth.

Source:
Wikipedia

June 24, 2015July 20, 2017 by Matt Williams

What is the Biggest Planet in the Solar System?

Jupiter and Io — Io and Jupiter as seen by New Horizons during its 2008 flyby. (Credit: NASA/Johns Hopkins University APL/SWRI).

Ever since the invention of the telescope four hundred years ago, astronomers have been fascinated by the gas giant of Jupiter. Between it’s constant, swirling clouds, its many, many moons, and its Giant Red Spot, there are many things about this planet that are both delightful and fascinating.

But perhaps the most impressive feature about Jupiter is its sheer size. In terms of mass, volume, and surface area, Jupiter is the biggest planet in our Solar System by a wide margin. But just what makes Jupiter so massive, and what else do we know about it?

Size and Mass:

Jupiter’s mass, volume, surface area and mean circumference are 1.8981 x 10²⁷ kg, 1.43128 x 10¹⁵ km³, 6.1419 x 10¹⁰ km², and 4.39264 x 10⁵ km respectively. To put that in perspective, Jupiter diameter is roughly 11 times that of Earth, and 2.5 the mass of all the other planets in the Solar System combined.

But, being a gas giant, Jupiter has a relatively low density – 1.326 g/cm³– which is less than one quarter of Earth’s. This means that while Jupiter’s volume is equivalent to about 1,321 Earths, it is only 318 times as massive. The low density is one way scientists are able to determine that it is made mostly of gases, though the debate still rages on what exists at its core (see below).

Composition:

Jupiter is composed primarily of gaseous and liquid matter. It is the largest of the gas giants, and like them, is divided between a gaseous outer atmosphere and an interior that is made up of denser materials. Its upper atmosphere is composed of about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules, and approx. 75% hydrogen and 24% helium by mass, with the remaining one percent consisting of other elements.

*This cut-away illustrates a model of the interior of Jupiter, with a rocky core overlaid by a deep layer of liquid metallic hydrogen. Credit: Kelvinsong/Wikimedia Commons*

The atmosphere contains trace amounts of methane, water vapor, ammonia, and silicon-based compounds as well as trace amounts of benzene and other hydrocarbons. There are also traces of carbon, ethane, hydrogen sulfide, neon, oxygen, phosphine, and sulfur. Crystals of frozen ammonia have also been observed in the outermost layer of the atmosphere.

The interior contains denser materials, such that the distribution is roughly 71% hydrogen, 24% helium and 5% other elements by mass. It is believed that Jupiter’s core is a dense mix of elements – a surrounding layer of liquid metallic hydrogen with some helium, and an outer layer predominantly of molecular hydrogen. The core has also been described as rocky, but this remains unknown as well.

In 1997, the existence of the core was suggested by gravitational measurements, indicating a mass of from 12 to 45 times the Earth’s mass, or roughly 4%–14% of the total mass of Jupiter. The presence of a core is also supported by models of planetary formation that indicate how a rocky or icy core would have been necessary at some point in the planet’s history in order to collect its bulk of hydrogen and helium from the protosolar nebula.

However, it is possible that this core has since shrunk due to convection currents of hot, liquid, metallic hydrogen mixing with the molten core. This core may even be absent now, but a detailed analysis is needed before this can be confirmed. The Juno mission, which launched in August 2011, is expected to provide some insight into these questions, and thereby make progress on the problem of the core.

The temperature and pressure inside Jupiter increase steadily toward the core. At the “surface”, the pressure and temperature are believed to be 10 bars and 340 K (67 °C, 152 °F). At the “phase transition” region, where hydrogen becomes metallic, it is believed the temperature is 10,000 K (9,700 °C; 17,500 °F) and the pressure is 200 GPa. The temperature at the core boundary is estimated to be 36,000 K (35,700 °C; 64,300 °F) and the interior pressure at roughly 3,000–4,500 GPa.

Moons:

The Jovian system currently includes 67 known moons. The four largest are known as the Galilean Moons, which are named after their discoverer, Galileo Galilei. They include: Io, the most volcanically active body in our Solar System; Europa, which is suspected of having a massive subsurface ocean; Ganymede, the largest moon in our Solar System; and Callisto, which is also thought to have a subsurface ocean and features some of the oldest surface material in the Solar System.

Then there’s the Inner Group (or Amalthea group), which is made up of four small moons that have diameters of less than 200 km, orbit at radii less than 200,000 km, and have orbital inclinations of less than half a degree. This groups includes the moons of Metis, Adrastea, Amalthea, and Thebe. Along with a number of as-yet-unseen inner moonlets, these moons replenish and maintain Jupiter’s faint ring system.

Jupiter also has an array of Irregular Satellites, which are substantially smaller and have more distant and eccentric orbits than the others. These moons are broken down into families that have similarities in orbit and composition, and are believed to be largely the result of collisions from large objects that were captured by Jupiter’s gravity.

*Illustration of Jupiter and the Galilean satellites. Credit: NASA*

Interesting Facts:

Much like Earth, Jupiter experiences auroras near its northern and southern poles. But on Jupiter, the auroral activity is much more intense and rarely ever stops. The intense radiation, Jupiter’s magnetic field, and the abundance of material from Io’s volcanoes that react with Jupiter’s ionosphere creates a light show that is truly spectacular.

Jupiter also has a violent atmosphere. Winds in the clouds can reach speeds of up to 620 kph (385 mph). Storms form within hours and can become thousands of km in diameter overnight. One storm, the Great Red Spot, has been raging since at least the late 1600s. The storm has been shrinking and expanding throughout its history; but in 2012, it was suggested that the Giant Red Spot might eventually disappear.

The discovery of exoplanets has revealed that planets can get even bigger than Jupiter. In fact, the number of “Super Jupiters” observed by the Kepler space probe (as well as ground-based telescopes) in the past few years has been staggering. In fact, as of 2015, more than 300 such planets have been identified.

Notable examples include PSR B1620-26 b (Methuselah), which was the first super-Jupiter to be observed (in 2003). At 12.7 billion years of age, it is also the third oldest known planet in the universe. There’s also HD 80606 b (Niobe), which has the most eccentric orbit of any known planet, and 2M1207b (Lerna), which orbits the brown dwarf Fomalhaut b (Illion).

Scientist theorize that a gas gain could get 15 times the size of Jupiter before it began deuterium fusion, making it a brown dwarf star. Good thing too, since the last thing the Solar System needs if for Jupiter to go nova!

Jupiter was appropriately named by the ancient Romans, who chose to name after the king of the Gods (Jupiter, or Jove). The more we have come to know and understand about this most-massive of Solar planets, the more deserving of this name it appears.

If you’re wondering, here’s how big planets can get with a lot of mass, and here’s what is the biggest star in the Universe. And here’s the 2nd largest planet in the Solar System.

Here’s another article about the which is the largest planet in the Solar System, and here’s what’s the smallest planet in the Solar System.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

Sources:

June 21, 2015May 6, 2016 by Matt Williams

How Many Moons Does Uranus Have?

Uranus and Moons — Uranus and its system of Moons. Credit: NASA/JPL

In the outer Solar System, there are many worlds that are so large and impressive to behold that they will probably take your breath away. Not only are these gas/ice giants magnificent to look at, they are also staggering in size, have their own system a rings, and many, many moons. Typically, when one speaks of gas (and/or ice) giants and their moons, one tends to think about Jupiter (which has the most, at 67 and counting!).

But have you ever wondered how many moons Uranus has? Like all of the giant planets, it’s got rather a lot! In fact, astronomers can now account for 27 moons that are described as “Uranian”. Just like the other gas and ice giants, these moons are motley bunch that tell us much about the history of the Solar System. And, just like Jupiter and Saturn, the process of discovering these moons has been long and involved on multiple astronomers.

Continue reading “How Many Moons Does Uranus Have?”