Astronomy Archives

July 26, 2009December 24, 2015 by Matt Williams

Symbols 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 ascribed behavior to the celestial bodies.

When it comes 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.

Consider the planet Mercury, 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 rotation 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. 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 is Jupiter’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.

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, it still has a 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.

Other Objects:
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.

*A full moon captured July 18, 2008. Credit: NASA/Sean Smith*

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 Sun god’s played in ancient pantheons.

The planets have played an important role in the culture and astrological systems of every human culture. Because of this, the symbols, names, and terms that denote them continue to hold special significance in our hearts and minds.

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.

Universe Today has articles you will want to check out on symbols for the Sun and Moon and symbol for Earth.

If you are looking for more information, take a look at this website from NASA on the astronomical symbols or on the symbol for Pluto.

Astronomy Cast has an episode on each planet, so listen to all of them in order starting with Mercury.

July 26, 2009December 24, 2015 by Abby Cessna

Orbits of the Planets

Take a look at the Solar System from above, and you can see that the planets make nice circular orbits around the Sun. But dwarf planet’s Pluto’s orbit is very different. It’s highly elliptical, traveling around the Sun in a squashed circle. And Pluto’s orbit is highly inclined, traveling at an angle of 17-degrees. This strange orbit gives Pluto some unusual characteristics, sometimes bringing it within the orbit of Neptune. Credit: NASA

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Centuries ago, people believed that the Earth was the center of the Solar System. Slowly, that view was replaced with the heliocentric view. With that change came the realization that the planets orbit the Sun.

When Pluto was reclassified as a dwarf planet, Mercury became the planet with the most eccentric orbit. The eccentricity of an orbit is a measurement of how much the orbit deviates from a circular shape. If an orbit is a perfect circle, it has an eccentricity of zero, and that number increases with an increase in eccentricity. Mercury has an eccentricity of .21. Its orbit ranges from 46 million kilometers at the closest point to the Sun to 70 million kilometers at the farthest point. The closest point to the Sun in an orbit is called the perihelion, and the farthest point is the aphelion. Mercury is the fastest planet to orbit the Sun at approximately Earth 88 days.

Venus has the least eccentricity of any planet in our Solar System – eccentricity of .007 – with a nearly perfect circular orbit. Venus’ orbit ranges from 107 million kilometers at the perihelion to 109 million kilometers from the Sun. It takes 224.7 of our days to orbit the Sun. A day on Venus is actually longer than a year because the planet rotates so slowly. Seen from the Sun’s north pole, all of the planets rotate counter-clockwise, but Venus actually rotates clockwise; it is the only planet to do that.

Earth also has a very low eccentricity of .017. On average, the planet is about 150 million kilometers from the Sun, but it can range from 147 million kilometers to 152 million kilometers. It takes our planet roughly 365.256 days to orbit the Sun, which is the reason for leap years.

Mars has an eccentricity of .093 making it one of the most eccentric orbits in our Solar System. Mars perihelion is 207 million kilometers and its aphelion is 249 million kilometers from the Sun. Over time, Mars’ orbit has become more eccentric. It takes 687 Earth days to orbit the Sun.

Jupiter has an eccentricity of .048 with a perihelion of 741 million kilometers and an aphelion of 778 million kilometers. It takes 4331 Earth days – 11.86 of our years – for Jupiter to orbit the Sun.

Saturn has an eccentricity of .056. At its closest point, Saturn is 1.35 billion kilometers from the Sun, and 1.51 billion kilometers away at its farthest point. Depending on what position it is in its orbit, Saturn’s rings are fully visible or almost invisible. The planet takes 29.7 years to orbit the Sun. In fact, since it was discovered in 1610, Saturn has only orbited approximately 13 times. Earth has orbited the Sun almost 400 times since then.

Uranus has a perihelion of 2.75 billion kilometers and an aphelion of 3 billion kilometers from the Sun. Its eccentricity is .047. It takes Uranus 84.3 Earth years to orbit the Sun. Uranus is unique because it actually rotates on its side with an axial tilt of almost 99°.

Neptune’s eccentricity is .009, almost as low as Venus’. The planet has a perihelion of 4.45 billion kilometers and an aphelion of 4.55 billion kilometers. Since Pluto was reclassified as a dwarf planet, Neptune is the planet with an orbit farthest from the Sun.

Universe Today has articles on orbits of all the planets including Mercury and Mars.

There are a number of other sites, including one with animations of the orbits and what an orbit is.

Astronomy Cast has an episode on the orbit of the planets.

July 26, 2009February 10, 2017 by Abby Cessna

What are the Sizes of the Planets?

It is often difficult to grasp just how large the planets actually are. There are a number of ways to measure a planet, including diameter, volume, and surface area.

Mercury is the smallest planet in our Solar System since Pluto was demoted to a dwarf planet. It has a diameter of 4,879 km, and a surface area of 17.48 x 10⁷ km², which is only about 11% of Earth’s surface area. Mercury’s volume is even smaller in comparison at 6.083 x 10¹⁰km³, which is only 5.4% the volume of Earth.

Venus is similar in size to Earth, which earned it the title of Earth’s twin. Venus has a diameter of 12,100 km and a surface area of 4.6 x 10⁸ km². These measurements are 95% and 90% of Earth’s diameter and surface area respectively. With a volume of 9.38 x 10¹¹ km³, Venus’ volume is 86% of Earth’s.

Earth has a diameter of 12,742 km and a surface area of 5.1 x 10⁸ km². Its volume of 1.08 x 10¹²km³ gives the planet the largest volume of any of the terrestrial planets.

Mars is also a small planet, the second smallest in our Solar System. Mars’ diameter is 6,792 km, only about 53% of Earth’s diameter. At only 28% of Earth’s surface area, Mars has a very small surface area of 1.45 x 10⁸km². Mars’ volume of 1.63 x 10¹¹ km³ is only 15% of Earth’s volume.

All of the gas giants are larger in size than the four inner planets. Jupiter is the largest planet in our Solar System. It has a diameter of 143,000 km, which is more than 11 times the size of Earth’s diameter. The numbers only get larger from there. Jupiter has a surface area of 6.22 x 10¹⁰ km². That is 122 times greater than Earth’s surface area. Jupiter’s volume of 1.43 x 10¹⁵ km³ is an incredible number. You can fit 1321 Earths inside Jupiter.

Saturn is the second largest planet in our Solar System. It has a diameter of 120,536 km across the equator, and a surface area of 4.27 x 10¹⁰ km². With a volume of 8.27 x 10¹⁴ km³, Saturn can hold 764 Earths inside.

Uranus has a diameter of 51,118 km and a surface area of 8.1 x 10⁹ km². Although Uranus is much smaller than Jupiter, it is still large. With a volume of 6.83 x 10¹³ km³, you could fit 63 Earths inside the gas giant.

Neptune is slightly smaller than Uranus, but still very large. The planet has a diameter of 49,500 km. You could fit 57.7 Earths inside Neptune, which has a volume of 6.25 x10¹³ km³. Neptune has a surface area of 7.64 x 10⁹ km², which is 15 times Earth’s surface area.

We have written many interesting articles about the Solar Planets here at Universe Today. Here’s tWhat are the Different Masses of the Planets?, What Is The Atmosphere Like On Other Planets?, What is the Average Surface Temperatures of the Planets? and What are the Diameters of the Planets?

For more information, check out this website to learn all about the planets and this page from NASA to learn about the planets.

Astronomy Cast has an episode on each of the planets including Mercury.

July 24, 2009December 24, 2015 by Tammy Plotner

Weekend SkyWatcher’s Forecast: July 24-26, 2009

Greetings, fellow SkyWatchers! Has everyone enjoyed the Apollo revival? I certainly have – and now the Moon is gently returning to evening sky and offering us great opportunities over the coming evenings to do a little bit of study with binoculars and telescopes. Look for its slender crescent just after sunset! This weekend we’re going to try an open cluster you may never have seen that works well for small optics and a Herschel object with a real twist. Need more? Then we’ll check out a beautifully colored double star, too… But not the one you expect! Grab your telescopes and binoculars and I’ll see you in the back yard…

Friday, July 24, 2009 – Today let’s start with the 1853 birth on this date of Henri-Alexandre Deslandres. Do you recognize his name from our lunar studies? He invented the spectroheliograph to photograph the Sun in monochromatic light! Deslandres also observed the spectra of planets and stars and measured their radial velocities. Did you see the very young crescent of the Moon during twilight? The Moon played an important role in history on this date. The Apollo 11 astronauts splashed down from their return from the Moon on this date in 1969! Only 15 years before, in 1954, the sound of a human voice had been reflected off the Moon’s surface and returned to Earth. James H. Trexler at the Naval Research Laboratory spoke into a microphone at the laboratory’s Maryland facility, and the sound was relayed back 2.5 seconds later. Although ‘‘Operation Moon Bounce’’ was only a repetition of vowel sounds, Trexler felt the project held promise as a communications and radar intercept device. It might be worth it to point out that many radars are very close to the theoretical possibility of contacting the Moon, and hence the practicality of building a system capable of intercepting these systems by reflections from the Moon is not beyond the realm of possibility.

Tonight we start with a group of young stars beginning their stellar evolution and end with an old solitary elder preparing to move onto an even ‘‘higher realm.’’ Open cluster IC 4665 is easily detected with just about any optical aid about a finger-width north-northeast of Beta Ophiuchi (RA 17 46 18 Dec +05 43 00). Discovered by Philippe Loys de Cheseaux in the mid-1700s, this 1,400 light year distant cluster consists of about 30 mixed-magnitude stars all less than 40 million years of age. Despite its early discovery, IC 4665 did not achieve broad enough recognition for Dreyer to include it in the late nineteenth-century New General Catalog (NGC), and it was later added as a supplement to the NGC in the Index Catalog of 1908. Be sure to use low power to see all of this large group.

Saturday, July 25, 2009 – Today we celebrate a success of the U.S.S.R. space program with the achievement of cosmonaut Svetlana Savitskaya, the first woman to walk in space (in 1982 on this date) and only the second female to go into space, preceding Sally Ride. Today is also the date of the 1973 launch of Soviet Mars 5 probe. Although it didn’t complete its full mission, it did send back 60 photos of the Martian Southern Hemisphere!

Although poor position makes study difficult during the first few lunar days, be sure to look for the ancient impact Vendelinus. Spanning 150 kilometers in diameter and with walls reaching up to 4,400 meters in height, lava flow has long ago eradicated any interior features. Its old walls hold mute testimony to later impact events such as crater Holden on the south shore, larger Lame on the northeast edge, and sharp Lohse northwest. Mark your challenge list!

Tonight’s challenge is Herschel I.44, also known as NGC 6104, a 9.5-magnitude globular cluster around two finger-widths northeast of Theta Ophiuchi and a little more than a degree due east of star 51 (RA 17 38 37 Dec –23 54 31). Discovered by William Herschel in 1784 and often classed as ‘‘uncertain,’’ this halo object has been pegged by today’s powerful as a Class VIII and given a rough distance from the galactic center of 8,800 light-years. Although neither William nor John could resolve this globular and listed it originally as a bright nebula, studies in 1977 revealed a nearby suspected planetary nebula named Peterson 1. Thirteen years later, further study revealed this wasn’t a nebula at all but evidence of a symbiotic star. Symbiotic stars are a true rarity—not a single star at all but a binary system. A red giant dumps mass toward a white dwarf in the form of an accretion disk. When this reaches critical mass, it then causes a thermonuclear explosion, resulting in a planetary nebula. Although no evidence exists that this object is located within metal-rich NGC 6401, just being able to see it in the same field makes this journey both unique and exciting!

Sunday, July 26, 2009 – On this date in 1969 in a vacuum-sealed room, the very first sample return of Moon rocks was studied.

Our own vacuum of space awaits as we view the area around Mare Crisium to have a look at this month’s lunar challenge—Macrobius.

You’ll find it just northwest of the Crisium shore. Spanning 64 kilometers in diameter, this Class I impact crater drops to a depth of nearly 3,600 meters—about the same as many of our Earthly mines. Its central peak rises to 1,100 meters and may be visible as a small speck inside the crater’s interior. Be sure to mark your lunar challenge lists, and look for other features you may have missed before!

Since the moonlight will now begin to interfere with our globular cluster studies, let’s waive these for a while as we take a look at some of the region’s most beautiful stars. Tonight your goal is to locate Omicron Ophiuchi, about a finger-width northeast of Theta (RA 17 18 00 Dec –24 17 02). At a distance of 360 light-years, the Omicron system is easily split by even small telescopes. The primary star is slightly dimmer than magnitude 5 and appears yellow to the eye. The secondary is near 7th magnitude and tends to be more orange in color. This wonderful star is on many doubles’ observing lists, so be sure to note it!

Are you wanting to keep an eye out for those dark markings of the Jupiter impact, too? Well, they’re there! Just remember if you’re new to astronomy that features on Jupiter rotate as the planet turns and we’re turning, too. Seeing the new “spots” requires some calculations and these areas will rotate into meridian view about 2 hours and 6 minutes after the Great Red Spot makes an appearance. Also remember that our own atmospheric seeing conditions play a great role as well! If it just so happens the dark spots will be making their appearance will Jupiter is still very low on the horizon, chances are your luck with seeing them in a small telescope won’t be high. But, don’t let that discourage you from looking! It doesn’t take long for a planet to rise to good observing height and the spots will stay visible for several hours as they rotate in and out on either side of your computed appearance time. (And don’t forget galiean moon shadow transits can also cause dark markings… but these will be very round!)

Until next week? Enjoy your observations and keep reaching for the stars!

This week’s awesome images are (in order of appearance): Henri Deslandres (historical image), IC 4665 (credit—Palomar Observatory, courtesy of Caltech), Vendelinus (credit—Alan Chu), NGC 6401 (credit—Palomar Observatory, courtesy of Caltech), Macrobius on the edge of Crisium (credit—Greg Konkel) Omicron Ophiuchi (credit—Palomar Observatory, courtesy of Caltech) and Jupiter (credit-Sky & Telescope: Sean Walker). We thank you so much!

July 24, 2009December 24, 2015 by Nancy Atkinson

Giant Soap Bubble In Space

The Cygnus Bubble. Credit: T. A. Rector/University of Alaska Anchorage, H. Schweiker/WIYN and NOAO/AURA/NSF

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What looks like a giant soap bubble or even perhaps just a water drop on a camera lens is actually a newly discovered planetary nebula. Dave Jurasevich of the Mount Wilson Observatory in California spotted the “Cygnus Bubble” while recording images of the region in July 2008. A few days later, amateur astronomers Mel Helm and Keith Quattrocchi also found it. Then, in 2009, the Kitt Peak Observatory pointed its 4-meter Mayall telescope at the object, and created the image above. Spectacular!

The bubble has been there awhile, and probably won’t “pop” anytime soon. The object was officially named PN G75.5+1.7 just last week. Astronomers have looked back at older images and found the object, just barely discernible in some images, such as this image below taken by Jurasevich.

Faint "Bubble" Nebula in Cygnus - Imaged on 05 July 2008 by Dave Jurasevich

A closer look at images from the second Palomar Sky Survey revealed it had the same size and brightness 16 years ago. Jurasevich thinks it was overlooked because it is very faint.

“It’s a beautiful example,” says Adam Frank of the University of Rochester, New York. “Spherical ones are very rare.” One explanation is that the image is looking down the throat of a typical cylindrical nebula. However, it is still remarkably symmetrical, Frank says.

For more about the history of observing this object, check out this post on Jurasevich’s Star Imager site.

Source: New Scientist

July 23, 2009December 24, 2015 by John Carl Villanueva

Alpha Particle

An alpha particle is a particle made up of two protons and two neutrons. Since this configuration is similar to that of a helium nucleus, it’s often referred to as a helium nucleus. The term is commonly used in nuclear physics, and is one of the three particles commonly emitted during a radioactive decay, i.e., alpha, beta, and gamma particles.

Alpha particles gained prominence during the early days of particle physics when scientists used them as projectiles to bombard certain targets. One of the most widely celebrated experiments that made use of alpha particles was that of Ernest Rutherford’s that led to the discovery of the atom’s structure.

Using alpha particles as projectiles and gold foils as targets, Rutherford was able to come to the conclusion that atoms were made up of very dense positively charged cores with the much lighter negatively-charged electrons orbiting around it. His conclusion was based on the observation that the trajectories of the alpha particles were slightly deviated (as expected) at most times but in rare instances bounced off like ping-pong balls thrown against a wall.

The alpha particles went through the gold foils unhindered when they passed through the large but sparsely filled region around the nucleus. However, when, during much rarer instances, they happened to collide head on or even came close to the very dense and positively charged nucleus, they were deflected at very wide angles.

Through this information, there was no other option but for Rutherford to conclude that the atom must have a very dense nucleus which is very much smaller compared to the entire atom.

In terms of atomic proportions, alpha particles are considered very massive because of the existence of the two protons and two neutrons. Furthermore, they are also positively charged due to the protons. As such, they can easily wreak havoc to most targets. That is, they have high ionization properties.

Alpha particles are released during alpha decay processes which can happen most especially to ultra-heavy nuclei like uranium, thorium, actinium, and radium. Since they’re not as fast (due mainly to their masses) as betas and gammas, they can’t travel across large distances and can be easily stopped by a piece of paper or human skin.

However, again because of their huge masses, alpha particles can be very dangerous whenever they can somehow enter the body through inhalation or ingestion. Minus that possibility, you don’t have to worry much about this heavyweight of a particle.

Universe Today has some interesting related content that you might want to read. Want to know about how the Opportunity rover got sidelined by a charged particle hit? And here’s an article about alpha radiation.

There’s more about it at NASA. Here are a couple of sources there:

Here are two episodes at Astronomy Cast that you might want to check out as well:

July 23, 2009December 24, 2015 by Brian Ventrudo

Happy 10th Birthday, Chandra X-Ray Observatory!

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Ten years ago, on July 23, 1999, NASA’s Chandra X-ray Observatory was deployed into orbit by the space shuttle Columbia. Far exceeding its intened 5-year life span, Chandra has demonstrated an unrivaled ability to create high-resolution X- ray images, and enabled astronomers to investigate phenomena as diverse as comets, black holes, dark matter and dark energy.

“Chandra’s discoveries are truly astonishing and have made dramatic changes to our understanding of the universe and its constituents,” said Martin Weisskopf, Chandra project scientist at NASA’s Marshall Space Flight Center in Huntsville, Ala.

The science generated by Chandra — both on its own and in conjunction with other telescopes in space and on the ground — led to a widespread, transformative impact on 21st century astrophysics. Chandra has provided the strongest evidence yet that dark matter must exist. It has independently confirmed the existence of dark energy and made spectacular images of titanic explosions produced by matter swirling toward supermassive black holes.

To commemorate the 10th anniversary of Chandra, three new versions of classic Chandra images will be released during the next three months. These images, the first of which was released today, provide new data and a more complete view of objects that Chandra observed in earlier stages of its mission. The image being released today is of the spectacular supernova remnant E0102-72.

“The Great Observatories program — of which Chandra is a major part — shows how astronomers need as many tools as possible to tackle the big questions out there,” said Ed Weiler, associate administrator of NASA’s Science Mission Directorate at NASA Headquarters in Washington. NASA’s other “Great Observatories” are the Hubble Space Telescope, Compton Gamma-Ray Observatory and Spitzer Space Telescope.

The next image will be released in August to highlight the anniversary of when Chandra opened up for the first time and gathered light on its detectors. The third image will be released during “Chandra’s First Decade of Discovery” symposium in Boston, which begins Sept. 22.

“I am extremely proud of the tremendous team of people who worked so hard to make Chandra a success,” said Harvey Tananbaum, director of the Chandra X-ray Center at the Smithsonian Astrophysical Observatory in Cambridge, Mass. “It has taken partners at NASA, industry and academia to make Chandra the crown jewel of high-energy astrophysics.”

Tananbaum and Nobel Prize winner Riccardo Giacconi originally proposed Chandra to NASA in 1976. Unlike the Hubble Space Telescope, Chandra is in a highly elliptical orbit that takes it almost one third of the way to the moon, and was not designed to be serviced after it was deployed.

The Chandra X-ray Observatory was named after the great Indian-born American astrophysicist Subrahmanyan Chandrasekhar, who served on the faculty at the University of Chicago for almost 60 years, winning the 1983 Nobel Prize in Physics for his work on explaining the structure and evolution of stars.

July 22, 2009December 24, 2015 by Anne Minard

Northern & Southern Aurorae Are Siblings, But Not Twins

Asymmetrical aurorae, courtesy of Karl Magnus Laundal and Nature

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Seen the Northern Lights and you’ve seen them all, hm? Not so.

It is commonly assumed that the aurora borealis in the Northern Hemisphere and the aurora australis in the Southern Hemisphere are mirror images of each other — but new research has revealed differences between the events.

The aurorae, commonly known as the Northern and Southern Lights, are spectacular natural light displays in the Earth’s upper atmosphere. The phenomenon is caused by charged particles from the solar wind striking atoms and molecules in the atmosphere.

It’s intuitive to think the Northern and Southern Lights are identical, because the charged particles causing the aurora follow the symmetric magnetic field lines connecting the two hemispheres.

But study co-authors Nikolai Østgaard and Karl Magnus Laundal, both of the University of Bergen in Norway, report in the journal Nature this week that there are differences between the phenomena.

“Here we report observations that clearly contradict the common assumption about symmetric aurora: intense spots are seen at dawn in the Northern summer Hemisphere, and at dusk in the Southern winter Hemisphere,” they write. “The asymmetry is interpreted in terms of inter-hemispheric currents related to seasons, which have been predicted but hitherto had not been seen.”

Østgaard and Laundal based their report on observations from a new set of global imaging cameras at each pole. The authors suggest that the observed asymmetry confirms the existence of inter-hemispheric, field-aligned currents related to the seasons, which had been predicted but never before observed.

Source: Nature

July 22, 2009December 24, 2015 by Anne Minard

Mystery Solved? New Clues Point to a Liquid Ocean on Enceladus.

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A liquid plume is spewing from Saturn’s icy moon Enceladus — but is it coming from heated ice on the surface, or a liquid ocean underneath?

Analysis of the plume’s chemistry, detailed in the Cassini (CICLOPS) image above and reported in Nature this week, may put the debate to rest.

Lead author Jack Hunter (J.H.) Waite, of the Southwest Research Institute in San Antonio, Texas and his colleagues say ammonia detected in the jets from Enceladus’ south pole provides the strongest evidence yet for the existence of liquid water beneath the surface.

A previous paper led by Frank Postberg of the University of Heidelberg in Germany, published in Nature just last month, reported the discovery of salts in E-ring particles derived from the plume, also suggestive of a liquid reservoir.

But Susan Kieffer of the University of Illinois at Urbana–Champaign and her colleagues proposed in a 2006 Science paper that warm ice is heated near the surface, causing dissociation of clathrate hydrates. And Nicholas Schneider, of the University of Colorado at Boulder, and his colleagues published a paper in the same Nature issue as Postberg’s team (June 24) — reporting that there’s not enough sodium in the plume to support a liquid ocean.

The ammonia may tip the scales, say the authors of the new paper.

“The presence of ammonia provides strong evidence for the existence of at least some liquid water, given that temperatures in excess of 180K have been measured near the fractures from which the jets emanate,” the authors write. “We conclude, from the overall composition of the material, that the plume derives from both a liquid reservoir (or from ice that in recent geological time has been in contact with such a reservoir) as well as from degassing, volatile-charged ice.”

Besides ammonia, the authors detected various organic compounds and deuterium — ‘heavy’ hydrogen abundant in the oceans of Earth. Ammonia, together with methanol and salts, acts as an antifreeze, allowing liquid water to exist at below-freezing temperatures. The authors suggest that preserving even a residual oceanic layer during cooling episodes would maintain conditions necessary for tidal heating and geologic activity.

Enceladus is one of only three moons in the Solar System known to be volcanically active. The plume of gas and particles is thought to make up Saturn’s outermost ‘E’ ring.

UT ran a story last month, when Nature ran two papers with different ideas about whether Enceladus harbors a liquid ocean. See that story here.

Source for text: Nature. Source for images: Cassini Imaging Central Laboratory for Operations (CICLOPS), with thanks to study co-author William Lewis for the tip.

July 22, 2009December 24, 2015 by Abby Cessna

Weight on Other Planets

Planets and other objects in our Solar System. Credit: NASA.

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Many children, and even adults, dream of visiting other planets and wonder what it would be like to stand on another planet. For one thing, your weight would be different on another planet, depending on a number of factors including the mass of the planet and how far you are away from the center of the planet.

Before we start, it’s important to understand that the kilogram is actually a measurement of your mass. And your mass doesn’t change when you go anywhere in the Universe and experience different amounts of gravity. Your weight is best measured in newtons. But since your bathroom doesn’t measure your weight in newtons, we’ll use kilograms. This is what your bathroom scale would say if you stepped on another world.

Mercury is the smallest planet in our Solar System, but it is dense. Because Mercury is so small, it has very little gravity. If you weighed 68 kg on Earth, you would only weigh 25.7 kg on Mercury.

Venus is very close to Earth in size and mass. Venus’ mass is roughly 90% of the mass of the Earth. Thus, it is no surprise that someone would weigh a similar amount on Venus. Someone who weighed 68 kg on Earth would weigh 61.6 kg on Venus.

Mars is quite a bit smaller than Earth with only 11% of our planet’s mass. Mars is larger than Mercury, but it is not as dense as the smaller planet. If you weighed 68 kg on Earth then you would weigh 25.6 kg on Mars. Since Pluto was demoted to a dwarf planet, Mars became the planet where you would weigh the least.

Jupiter is the largest planet in our Solar System with the most mass. Because of Jupiter’s mass, you would weigh more on that planet than on any other one in our Solar System. If you weighed 68 kg on Earth then you would weigh 160.7 kg on Jupiter, over twice your normal weight. That is if you could actually stand on Jupiter’s surface, which is impossible because it is a gas giant, and gas giants do not have solid surfaces.

Saturn is a gas giant best known for its planetary rings system. It is also the second biggest planet in our Solar System. Despite its mass though, the planet has a very low density and a lower gravity than Earth. If you weighed 68 kg on Earth, you would weigh 72.3 kg on Saturn.

Uranus is a gas giant without a solid surface. Although Uranus is larger in size than Neptune, it has less mass and therefore less gravity. You would only weigh 60.4 kg on Uranus, if you weighed 68 kg on Earth.

Neptune, the last planet in our Solar System, is a gas giant. If you weighed 68 kg on Earth, then you would weigh 76.5 kg on Neptune if you could stand on the planet’s surface.

Although the Moon is not a planet, it is one of the few objects that astronauts have actually visited. Because the Moon is so small, it has a low density and low gravity. If you weighed 68 kg on Earth, then you would only weigh 11.2 kg on the Moon.

Universe Today has a number of articles to check out including weight on the moon and mass of the planets.

If you are looking for more information then determine your weight on other planets and facts about the planets.

Astronomy Cast has an episode on gravity.