Astronomy Archives

December 30, 2009December 24, 2015 by Fraser Cain

Distance to Alpha Centauri

Alpha Centauri is the closest known star system to the Solar System. Also known as Rigil Kentaurus, Alpha Centauri is actually a multiple star system. It’s certainly a binary star, with two sunlike stars orbiting one another. And there’s also a red dwarf star, Proxima Centauri, which astronomers still argue about whether it’s part of the system.

The closest star in the group is Proxima Centauri, located only 4.243 light-years from the Sun. And then the Alpha Centauri AB stars are located 4.37 light-years away.

With the unaided eye, Alpha Centauri looks like a single star. But then under the power of a telescope, it’s possible to split them and see the individual stars separately. Alpha Centauri is only really prominent in the southern skies, and below the horizon to astronomers in the north.

Alpha Centauri A is slightly larger and more luminous than the Sun, while Alpha Centauri B is smaller and cooler than the Sun. But Proxima Centauri is a tiny red dwarf star, with only 1/8th the mass of the Sun.

We’ve written several articles about the Alpha Centauri system. Here’s an article about how we might be able to detect Earthlike planets around Alpha Centauri, and here’s an article about the sounds of Alpha Centauri.

Here’s a cool image of Alpha Centauri at Astronomy Picture of the Day.

We’ve also recorded an episode of Astronomy Cast about what it might take to travel to Alpha Centauri. Listen here, Episode 145: Interstellar Travel.

December 29, 2009December 24, 2015 by Fraser Cain

How Was Venus Discovered?

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Venus is one of the planets visible with the unaided eye. In fact, Venus is the brightest object in the sky, after the Sun and the Moon. So it’s impossible to know how was Venus discovered. The planet has been known about since prehistoric times. Perhaps a better question is, when did we realize that Venus was a planet?

Thousands of years ago, the Greek astronomers thought that the Earth was the center of the Universe, and everything revolved around us, including the Sun, the Moon, the planets and the stars. But in the in the 1500s, Nicolaus Copernicus developed his theories of a Sun-centered Solar System. Instead of the traditional idea, the Sun was at the center, and the Earth was just another planet like Venus and Mars.

This theory was given a tremendous amount of evidence when Galileo Galilei first turned his rudimentary telescope on Venus, showing that the planet went through phases, like the Moon. This meant that it orbited the Sun, and not the Earth. Galileo also discovered the 4 major moons orbiting Jupiter, demonstrating that not all objects in the Universe orbited the Earth.

So it was in the 16th and 17th centuries that astronomers really came to understand that both Venus and Earth were just planets orbiting the Sun.

We’ve written many articles about the discovery of planets for Universe Today. Here’s an article about how Uranus was discovered, and here’s how Neptune was discovered.

And if you’d like more info on Venus, check out Hubblesite’s News Releases about Venus, and here’s a link to NASA’s Solar System Exploration Guide on Venus.

We’ve also recorded an episode of Astronomy Cast all about Venus. Listen here, Episode 50: Venus.

December 29, 2009December 24, 2015 by Jon Voisey

Galactic Building Blocks

The current view of galactic formation is that galaxies form from a “bottom-up” method. In this picture, small dwarf galaxies, full of metal poor stars, were attracted by dark matter halos in the early universe which merged into larger galaxies. Many of those metal poor stars can still be seen today in the halo of the galaxy, but it was thought that the building blocks from which the galaxies were constructed were long gone or had evolved on their own and would no longer resemble the primordial building blocks.

However, earlier this year, an extremely metal poor star with only 0.00025% of the iron in the Sun was discovered in the Sculptor dwarf galaxy. If confirmed, this would show a strong link to further support the notion that metal poor dwarf galaxies were related to the metal poor stars that still populate our halo. Confirming this was the subject of a recent paper.

For their study, the authors analyzed the newly discovered star (S1020549) with a high resolution spectrograph. From this, they confirmed that the star had very little iron present (an element generally used as an indicator of overall heavy element abundance since its absorption lines feature prominently in the spectra and are easily detectable). The extremely low ratio of iron to hydrogen makes it currently the most metal poor star known in a dwarf galaxy (the overall record holder for metal deficiency is HE 1327–2327).

The study determined an overall [Fe/H] abundance of -3.8 (see how this abundance is defined here) which is very similar to the [Fe/H] abundance of archetypical halo stars of about -4.0. Furthermore, many of the other elemental abundances that were uncovered with the detailed spectroscopy (especially those of Mg, Ca, Sc, Ti, and Cr) also fit the general abundance level of stars found in our halo.

This isn’t a conclusive tie between the two and more such stars will need to be uncovered to reinforce the similarities, but since S1020549 was discovered with “a relatively modest survey” this may suggest “that future observational searches should discover more such objects in Sculptor and other dwarf galaxies.”

December 29, 2009December 24, 2015 by Steve Nerlich

Wolfram Alpha – A Handy Tool for the Casual Astronomer.

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We are not quite at that point where you can ask your computer to swing over to the Orion Nebula and take a few shots for next weeks’ astrophotography competition – oh and a cup of Earl Grey, hot, thanks.

But every day seems to get us that little bit closer.

If I want to know where Mintaka is in the night sky, I could start up a planetarium software program like Stellarium, or the legion other planetarium programs and web-based sky mapping sites to choose from.

But, being a ‘just point in the general direction and muck about until you find it’ type of telescope user, I’m much more interested in an objects’ alt-azimuth position from my particular location, rather than trying to set my scope to right ascension, declination settings. Seriously, I am holding off on starting my astrophotography career until those Go To computers can make a proper cup of tea.

Anyway my point is, even with all these great information resources around, things are still a bit all over the place. Wouldn’t it be great if there was one place where you could go to find out – well, anything? Wolfram Alpha seems to be taking steps in that direction. It’s kind of a front end interface drawing on a huge virtual warehouse of databases.

As well as the basic search engine, there’s a wiki sideline to all this, notably a set of Wolfram Astronomy demonstration projects here, including a downloadable 3d celestial sphere, a planet database and why not a simplified model of the Big Bang.

And it knows where you live. At least it knows where I live, I guess from my IP address, so I save a step there. Wolfram Alpha can tell me Mintaka is set to rise at 6.01pm local time, it’s 720 light years away and it will set at 6.07 am. And any time I like, I can just hit refresh and get its alt-azimuth position updated in real time. It can do the same for the planets and for the ISS too. Not too shabby.

Also useful for the casual astronomer, if you type in your city, it will give you a weather report – and even a population count if you like. And from there you might find yourself straying further off topic. For example, I now know there are 202,185 people alive named Steve – which is only 1 in every 1,173 people. Hah.

And if you do type in Tea. Earl Grey. Hot.? It says Coming right up. Can’t wait.

December 28, 2009December 24, 2015 by Fraser Cain

Largest Moon of Saturn

The largest moon of Saturn is Titan, measuring 5,150 km across. In fact, Titan is the second largest moon in the Solar System, after Jupiter’s Ganymede. Titan is so big that it’s even larger than planet Mercury, which is only 4,879 km across. And it’s much bigger than the Earth’s moon at 3,474 km.

Astronomers used to think that Titan was actually the largest moon in the Solar System, but when NASA’s Voyager spacecraft first arrived at the moon in the 1980s, they were able to make detailed observations of the moon at its atmosphere. They proved that Titan’s atmosphere extended out for dozens of kilometers, and so the physical moon itself was actually smaller than previously thought, making it smaller than Ganymede.

Titan orbits Saturn at an average distance of 1,221,870 km, completing an orbit every 15.945 days. It’s tidally locked to Saturn, so it always presents the same face to Saturn. So a day on Saturn is also the same amount of time it takes to orbit Saturn.

Titan is the only moon in the Solar System known to have a thick atmosphere. In fact, the pressure of the atmosphere on the surface of Saturn is 1.5 times greater than the atmospheric pressure here on Earth. Of course, the atmosphere of Titan is almost entirely nitrogen, and the temperature is -179° C. So it wouldn’t be a comfortable place to visit without a spacesuit.

We’ve written many articles about Titan for Universe Today. Here’s an article about seasonal changes on Titan, and here’s an article about how Titan’s haze acts like an ozone layer.

If you’d like more info on Titan, check out Hubblesite’s News Releases about Saturn. And here’s a link to the homepage of NASA’s Cassini spacecraft, which is orbiting Saturn.

We’ve also recorded an episode of Astronomy Cast just about Saturn’s moons. Listen here, Episode 61: Saturn’s Moons.

December 28, 2009December 24, 2015 by Fraser Cain

Moon Rotation

The rotation of the Moon is a strange situation. It takes the same amount of time for the Moon to complete a full orbit around the Earth as it takes for it to complete one rotation on its axis. In other words, the Moon rotation time is 27.3 days, just the same as its orbital time: 27.3 days.

What this means to us here on Earth is that the Moon always presents the same face to the Earth. We only see one side of the Moon, and not the other. And if you could stand on the surface of the Moon, the Earth would appear to just hang in the sky, not moving anywhere.

Astronomers say that the Moon is tidally locked to the Earth. At some point in the past, it did have a different rotation rate from its orbital period. But slight differences in the shape of the Moon caused the Moon to experience different amounts of gravity depending on its position. These differences acted as a brake, slowing the Moon rotation speed down until it matched its orbital period. There are other tidally locked moons in the Solar System. Pluto and its moon Charon are tidally locked to each other, so they always present the same face to one another.

We’ve written many articles about rotation for Universe Today. Here’s an article about the rotation of the Earth, and here’s an article about the rotation of Saturn.

If you’d like more info on the Moon, check out NASA’s Solar System Exploration Guide on the Moon, and here’s a link to NASA’s Lunar and Planetary Science page.

We’ve also recorded an episode of Astronomy Cast all about the Moon. Listen here, Episode 113: The Moon, Part 1.

December 28, 2009December 24, 2015 by Fraser Cain

How Big is the Moon?

Earth Moon Comparison. Image credit: NASA

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The Moon is one of the most significant objects in the night sky, second only in brightness to the Sun. So, how big is the Moon?

The diameter of the Moon is only 3,474 km across. Just for comparison, the diameter of the Earth at the equator is 12,756 km. That’s only 27% the diameter of the Earth. The Moon is also the 5th largest moon in the Solar System, after Ganymede, Titan, Callisto and Io.

In terms of volume, the Moon only contains 2.195 x 10¹⁰ km³. That sounds like a lot of cubic kilometers of Moon, but again, that’s only 2% the volume of Earth.

The surface area of the Moon is 3.793 x 10⁷ km². That’s about the same size as Russia, Canada and the United States combined.

The circumference of the Moon is 10,921 km. Again, that’s only a little over a quarter the circumference of the Earth.

We’ve written many articles about the Moon for Universe Today. Here’s an article about the Moon compared to Earth, and here’s an article about the mass of the Moon.

If you’d like more info on the Moon, check out NASA’s Solar System Exploration Guide on the Moon, and here’s a link to NASA’s Lunar and Planetary Science page.

We’ve also recorded several episodes of Astronomy Cast about the Moon. Listen here, Episode 113: The Moon, Part 1.

December 28, 2009December 24, 2015 by Abby Cessna

Flat Earth Society

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The Flat Earth Society is an organization whose members adhere to the belief that the Earth is flat rather than a sphere. Although it would seem that this organization was founded before the fourth century B.C., when Greek philosophers and scientists advanced the idea of a spherical planet, it was not. Instead, it was founded in 1956 by Samuel Shenton who was a Fellow of both the Royal Astronomical Society and the Royal Geographic Society. He believed that his theory was based on common sense and scientific evidence and did not believe that scientists had enough proof to ascribe to the view of a spherical Earth.

When Shenton died in 1971, the organization was taken over by Charles Johnson and the society’s headquarters were moved from England to California. Johnson inherited much of Shenton’s large library containing flat earth literature when he took over the organization. Johnson claimed that there was a conspiracy against the theory of a flat earth. The new president of the organization also thought that the Sun and Moon were flat discs about 4,800 kilometers from Earth and that the stars were only approximately 6,400 kilometers from our planet.

When Samuel Shenton was presented with the pictures taken by probes from space showing a spherical Earth, he wavered at first. He restated his position though and said that the photographs could easily fool the untrained eye and that they had been faked. The Flat Earth Society also declared that the 1969 Moon landing was a hoax and it had been scripted and filmed. The Flat Earth Society took some of its philosophy from the Bible, claiming that the creation text shows that the Earth was created flat. Johnson in particular quoted biblical passages in his newsletters. Johnson also turned to the United Nations’ flag for proof of a flat earth. The globe portrayed on the flag looked similar to the model of a flat earth as described by the Flat Earth Society.

The Flat Earth Society began to decline in membership during the 1990’s, and it came to an end when Charles Johnson passed away in 2001. After the Flat Earth Society disbanded, several other groups seemed to have made use of its name at one time or another. There are number of flat earth forums and websites up and running. Even though at least one group has borrowed the Flat Earth Society’s name, it may not be directly connected to the old organization.

Universe Today has articles on is the Earth round and who discovered the Earth.

You should also check out the Flat Earth and do they really think the Earth is flat.

Astronomy Cast has an episode on Earth.

Sources:
http://en.wikipedia.org/wiki/Flat_Earth_Society
http://science.howstuffworks.com/space-conspiracy-theory8.htm

December 27, 2009December 24, 2015 by Jerry Coffey

Celestial Body

[/caption]The term celestial body is as expansive as the entire universe, both known and unknown. By definition a celestial body is any natural body outside of the Earth’s atmosphere. Easy examples are the Moon, Sun, and the other planets of our solar system. But those are very limited examples. The Kuiper belt contains many celestial bodies. Any asteroid in space is a celestial body. So, what do you write about with such a broad topic? How about a sampling of five of my favorites and leave it at that for now? Which five, though. Well, let’s cover Ceres, the Kuiper belt, the asteroid Cruithne, Achernar, and Apophis.

Ceres is a celestial body that is by far the largest and most massive asteroid in the belt between Mars and Jupiter. It is approximately the size of Texas or 975km x 909 km with a mass of 9.5×10²⁰. It actually represents 1/3 of all of the mass of the asteroid belt. It has enough mass for self gravity which is a major requirement to be considered a dwarf planet. It revolves around the sun every 1679.819 days with a very small axial tilt. The surface is relatively warm. The high temperature is thought to be in the neighborhood of -38°C(235 K). Ceres has a visual brightness magnitude of +6.9 to +9. When it is at the brightest point possible, Ceres is nearly bright enough to be seen with the naked eye. It can be seen with binoculars whenever it is above the horizon on a completely dark night.

The Kuiper belt contains many a celestial body. It is actually a disk-shaped region in the outer solar system lying beyond the orbit of Neptune and extending to a distance of about 50 astronomical units, containing thousands of small icy bodies, some of which are on highly elliptical orbits, periodically visiting the inner solar system as comets. It is thought to be a collection of the remnants of the formation of the solar system. Who knows what may be found when we are able to send spacecraft to its edges?

As a celestial body, the asteroid Cruithne is sort of small and indistinct until you consider that it is locked in a 1:1 orbit with the Earth. The asteroid is sometimes referred to as the Earth’s second moon. It is not a true moon because the Earth’s gravity does not effect it nor does its effect the Earth. Cruithne’s nearest pass to Earth is .1 AU (40 moon lengths), although right now it never comes closer than .3 AU. The asteroid sort of runs like a corkscrew around the Earth while both are revolving around the Sun. The asteroid Cruithne is in a normal elliptic orbit around the Sun. Its revolution around the Sun, approximately 364 days at present, is almost equal to that of the Earth. Because of this, Cruithne and Earth appear to follow each other in their paths around the Sun.

The celestial body Achernar is a bright, blue, B3-type star of six to eight solar masses lying approximately 144 light years away. It is classified as a dwarf, but it is 3,000 times more luminous than our Sun. It is in the deep southern sky and never rises above 33°N. Achernar is best seen from the southern hemisphere in November; it is circumpolar below 33°S. Achernar spins so quickly that is spherical in shape. The distance along its equator is 50% greater than its polar diameter. It is the brightest star in the Eridanus constellation. It is also the 9th brightest star in the night sky. Of the 10 brightest stars, other than our Sun, it is the hottest and bluest.

The celestial body Apophis is one of the most intriguing, to me. It is the stuff that many sci-fi legends have been based on. Apophis is most famous for the stir it caused in 2004. The asteroid was discovered on its way towards the Earth and was predicted to have a 2.7% chance of impacting the Earth. That in and of itself is not significant. Objects impact the Earth on a yearly basis. The size of Apophis was the major concern. Even a small chance that an asteroid the size of a small town hitting the Earth rightly caused a large commotion. It achieved the highest score ever on the Torino scale and it stayed on an elevated level for longer than any other asteroid ever has. It was eventually studied enough to know that it would not hit the Earth in 2004. The asteroid will pass again in 2029. Scientists predict that it will not hit the Earth, but it may pass through a gravitational keyhole that could alter its orbit enough that it could impact in 2036. The chances are slight, but real. Even if it doesn’t hit a keyhole in 2029 it will return every seven years and may pose a serious threat in the future. Scientists have proposed that Apophis be nudged out of its present orbit into an orbit that takes it further from the keyhole. NASA scientist David Morrison says, “After 2029, the deflection would have to be vigorous enough to miss not just a tiny keyhole but the much larger target of the Earth itself. And such a deflection is far beyond present technology for an asteroid this large.”.

Many things can make a celestial body interesting. Everyone has their favorites. Mine happen to be the five I have listed. Each can be further researched here on Universe Today. Follow these links to find what you need: Ceres, the Kuiper belt, the asteroid Cruithne, Achernar, and Apophis. Astronomy Cast offers a good episode about the mind-boggling possibility of multiple universes. Here’s a list of the 10 brightest stars.

Sources:
http://planetary.org/explore/topics/asteroids_and_comets/ceres.html
http://userpages.umbc.edu/~gwilson/kuiper.html
http://www.astro.uwo.ca/~wiegert/3753/3753.html
http://en.wikipedia.org/wiki/Achernar
http://neo.jpl.nasa.gov/apophis/

December 24, 2009December 24, 2015 by Ken Kremer

Santa’s Helpers arrive at ISS bearing Christmas Gifts

5 of Santa’s helpers round out the Expedition 22 crew aboard the ISS. Front row: Jeff Williams (left), Maxim Suraev. Back row: Oleg Kotov, T.J. Creamer and Soichi Noguchi.

In a stunning surprise, Santa’s helpers and elves floated into the International Space Station (ISS) on Tuesday (Dec. 22) bearing a Christmas tree, massive (but weightless) sacks of presents and boundless cheer. They had departed Earth from frigid Baikonur on Dec 20. The supposed cosmonauts and astronauts had apparently been magically transformed just moments before docking at the ISS. Without notice they were summarily pressed into Santa’s elite “Good Will” corps for special duty to bring holiday cheer and good tidings to all, especially all of Earth’s Children !
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After opening the hatches between their Soyuz TMA 17 capsule and the ISS, the newly christened helpers popped into view led by a smiling Oleg Kotov. He proudly hoisted the precious Christmas Tree ahead, topped by a dangling Santa. Although Santa was clearly honored to be first aboard, he didn’t quite know which way was up and was briefly heard to be asking about the safety briefing on climbing down the newly installed Space Chimney on last week’s daring and first of its kind Spacewalk.

Expedition 22 crew of 5 Elite Santa helpers and elves wearing festive holiday hats inside the Zvezda Service Module adorned with Christmas tree. Credit: Santa

Soichi Noguchi lugging massive sacks of Christmas presents through hatch into ISS, with no prior training ! Credit: Santa

Soichi Noguchi was next to float through, carefully navigating forwards with a giant white sack of presents slung over his shoulder so as not to damage the station walls. No black coal evident here ! Bringing up the rear was the lone Elf, Tim Creamer, sporting genuine pointy elf ears and elegant elven crafted shoes.

Two more of Santa’s helpers, Jeff Willams and Maxim Sureav, were already aboard the ISS and busy hanging Christmas stockings and decorations for the new arrivals.

After cobbling together the last presents for Santa’s world wide journey, the crew will bid Santa Adieu for the inaugural Chimney ride back to Earth. Good Luck Santa ! It’s a long but thrilling way down.

On Christmas Day the Expedition 22 crew will relax before beginning the busy final assembly of the ISS.

Meanwhile another special Santa squad is burning the midnight oil to finish last minute requests from the very best children and keeping Space Shuttle Endeavour toasty warm at the toy workshop inside her big house (Vehicle Assembly Building) at the Kennedy Space Center.

Merry Christmas and Happy Holiday’s to All !

Peace be with you