Posted on by Tammy Plotner

The Weekend SkyWatcher’s Forecast: May 9-11, 2008

Atlas Map

Greetings, fellow SkyWatchers! Are you ready for a very incredible weekend? The action begins on Friday as we take you on a guided tour of the lunar surface. On Saturday, celebrate Astronomy Day with a very special unaided eye sky event and a return to the Moon. No rest for the wicked on Sunday… Because you’ll be seeing double! Time to get out your binoculars and telescopes and turn an eye to the sky, because…. Here’s what’s up!

Friday, May 9 – Today in 1962, the first Earth-based laser was aimed at crater Albategnius. Although it isn’t visible tonight, let’s take a look at what is visible just 1.5 light-seconds away! First is a Lunar Club challenge which won’t prove difficult because you’ll be working with a map. Relax! This will be much easier than you think. Starting at Mare Crisium, move along the terminator to the north following the chain of craters until you identify a featureless oval which looks similar to Plato seen on a curve. This is Endymion…and if you can’t spot it, don’t worry. Let’s take a look at some features which will point you to it!

Most prominent of all will be two craters to the north named Atlas and Hercules. The easternmost Atlas was named for the mythical figure who bore the weight of the world on his shoulders, and the crater spans 87 kilometers and contains a vivid Y-shaped rima in the interior basin. Western Hercules is considerably smaller at 69 kilometers in diameter, and shows a deep interior crater called G. Power up and look for the tiny E crater which marks the southern crater rim. North of both is another unusual feature which many observers miss. It is a much more eroded and far older crater which only shows a basic outline and is only known as Atlas E.

Since we’re here, let’s take a crater walk and see how many features we can identify… Good luck, and clear skies!

Atlas Map

(1) Mare Humboldtianum, (2) Endymion, (3) Atlas, (4) Hercules, (5) Chevalier, (6) Shuckburgh, (7) Hooke, (8) Cepheus, (9) Franklin, (10) Berzelius, (11) Maury, (12) Lacus Somniorum, (13) Daniel, (14) Grove, (15) Williams, (16) Mason, (17) Plana, (18) Burg, (19) Lacus Mortis, (20) Baily, (21) Atlas E, (22) Keldysh, (23) Mare Frigoris, (24) Democritus, (25) Gartner, (26) Schwabe, (27) Thales, (28) Strabo, (29) de la Rue, (30) Hayn.

Saturday, May 10 – Today is Astronomy Day and something wonderful is happening in the sky! Somewhere out there, the Moon is silently occulting Mars, and the Red Planet will be hauntingly close to the limb as the skies darken… For observers through India and Europe, you have the chance to watch the occultation, so visit IOTA for specific times in your location!

Fabricius

Tonight let’s journey to the Moon as we look at a beautiful series of craters – Fabricius, Metius and Rheita. Bordered on the south by shallow Jannsen, Lunar Club challenge Fabricius is a 78 kilometer diameter crater highlighted by two small interior mountain ranges. To its northeast is Metius, which is slightly larger with a diameter of 88 kilometers. Look carefully at the two. Metius has much steeper walls, while Fabricius shows differing levels and heights. Metius’ smooth floor also contains a very prominent B crater on the inside of its southeast crater wall. Further northeast is the lovely Rheita Valley which stretches almost 500 kilometers and appears more like a series of confluent craters than a fault line. 70 kilometer diameter crater Rheita is far younger than this formation because it intrudes upon it. Look for a bright point inside the crater which is its central peak.

Since tonight will be our last chance to galaxy hunt for a while when the Moon has westered, let’s take a look at one of the brightest members of the Virgo Cluster – M49. Located about eight degrees northwest of Delta Virginis almost directly between a pair of 6th magnitude stars (RA 12 29 46 Dec +07 59 59), the giant elliptical M49 holds the distinction of being the first galaxy in the Virgo cluster to be discovered – and only the second beyond our local group. At magnitude 8.5, this type E4 galaxy will appear as an evenly illuminated egg shape in almost all scopes, and as a faint patch in binoculars. While a possible supernova event occurred in 1969, don’t confuse the foreground star noted by Herschel with something new!

Although most telescopes won’t be able to pick this region apart – especially with the Moon so near – there are also many fainter companions near M49, including NGC 4470. But a sharp-eyed observer named Halton Arp noticed them and listed them as Peculiar Galaxy 134 – one with “fragments!”

Sunday, May 11 – Tonight no two lunar features in the north will be more prominent than Aristoteles and Eudoxus. Viewable even in small binoculars, let’s take a closer look at larger Aristoteles to the north.

Aristoteles

As a Class I crater, this ancient old beauty has some of the most massive walls of any lunar feature. Named for the great philosopher, it stretches across 87 kilometers of lunar landscape and drops below the average surface level to a depth of 366 meters – a distance which is similar to Earth’s tallest waterfall, the Silver Cord Cascade. While it has a few scattered interior peaks, the crater floor remains almost unscarred. As a telescopic Lunar Club challenge, be sure to look for a much older crater sitting on Aristoteles’ eastern edge. Tiny Mitchell is extremely shallow by comparison and only spans 30 kilometers. Look carefully at this formation, for although Aristoteles overlaps Mitchell, the smaller crater is actually part of the vast system of ridges which supports the larger one.

PorrimaWhen you’re done, let’s have a look at another delightful pair that’s joined together – Gamma Virginis…

Better known as Porrima, this is one cool binary; whose members are nearly equal in spectral type and brightness. Discovered by Bradley and Pound in 1718, John Herschel was the first to predict this pair’s orbit in 1833 and state that one day they would become inseparable to all but the very largest of telescopes – and he was right. In 1920 the A and B stars had reached their maximum separation, but during 2007 they were as close together as they will ever be in our lifetimes. Observed as a single star in 1836 by William Herschel, its 171 year periastron now puts Porrima almost the same position as it was when Sir William saw it!

Have a great weekend… 😉

This week’s awesome images: Atlas Crater Map Image: Greg Konkel Annotations: Tammy Plotner – Fabricius, Metius and Rheita – Credit: Alan Chu – Aristoteles – Credit: Wes Higgins – Gamma Virginis: Porrima – Credit: Palomar Observatory, courtesy of Caltech. Thank you!!

Posted on by Ian O'Neill

After the Shuttle, Should Astronauts be Launched on Satellite Rockets?

The Atlas V rocket - a workhorse for getting satellites into orbit (NASA)

When the Shuttle fleet is retired in 2010, what other mode of transport could be used to take NASA astronauts into space? After all, we routinely launch satellites into orbit, why can’t the same technology be adapted and used for human spaceflight? Well, the US Senate committee on space and aeronautics was told by a retired US Air Force general on Wednesday that this option should be considered. Rather than injecting billions to accelerate development of the Orion space vehicle or becoming dependent on the Russian Soyuz, the reliable workhorses of satellite launches, the Atlas V and Delta IV rockets, could be “human rated”…

Concern is growing for the gap in the US ability to get astronauts into space between 2010 (when the Shuttle fleet is retired) and 2015 (the scheduled completion of Orion spacecraft and Ares rocket). As voiced on Tuesday by record breaking astronaut John Glenn, to depend on the Russian Soyuz system could prove problematic. This concern has been echoed by former US Air Force general Robert S. Dickman and has outlined a possible solution to the five-year gap. For a modest $500 million to $1 billion, the Atlas V and Delta IV launch systems (more accustomed to blasting communication satellites and military payloads into orbit) could be adapted to carry astronauts into space, and supplying the International Space Station. The only other way to reduce the gap would be to accelerate the Constellation Program, or (as voiced by Glenn on Tuesday) extend the Shuttle program. Unfortunately, both of these options would be disproportionately expensive.

So, converting satellite rockets might be a nice compromise; reduce the dependence on other space agencies, keep costs low and keep space open to manned space flight for NASA. Sounds like the perfect solution…

However, a top NASA official who worked on the Gemini and Apollo programs had a sobering reply for this possibility. Eugene Kranz told the US Senate committee that human rating existing rockets is no easy task. Kranz was involved in converting Titan and early Atlas rockets so they could be used for the manned Mercury an Apollo missions. Unfortunately, although this option looks attractive on paper, in reality, much more investment is required – often larger, unforeseen modifications are needed.

In the case of the Titan and Atlas modifications, the human rating took several years to complete. Unfortunately, 2010 is only two years away, modifying existing rockets sufficiently simply will not be completed on time.

Where NASA may not convert the rockets, private space corporations might. The company SpaceDev is looking into converting the Atlas V rocket, incorporating its Dreamchaser capsule as part of the plan to offer commercial ferrying of NASA astronauts to the ISS. Bigalow Aerospace and Lockheed Martin are hot on their tails, proposing human rating the Atlas V for trips to future Bigalow space hotels.

Source: New Scientist Blog

Posted on by Ian O'Neill

Stars Orbiting Close to Black Holes Flattened like Hot Pancakes

A star orbiting a black hole (NASA)

Playing with black holes is a risky business, especially for a star that is unlucky enough to be orbiting one. Assuming an unfortunate star hasn’t already had all of its hydrogen fuel and other component elements stripped from its surface, the powerful tidal forces will have some fun with the doomed stellar body. First the star will be stretched out of shape and then it will be flattened like a pancake. This action will compress the star generating violent internal nuclear explosions, and shockwaves will ripple throughout the tormented stellar plasma. This gives rise to a new type of X-ray burst, revealing the sheer power a black hole’s tidal radius has on the smaller binary sibling. Sounds painful…

It is intriguing to try to understand the dynamics near a supermassive black hole, especially when a star strays too close. Recent observations of a distant galaxy suggests the material pulled from a star near the center of a galactic nucleus caused a powerful X-ray flare which echoed from the surrounding molecular torus. The infalling stellar gas was sucked into the black hole’s accretion disk, generating a huge quantity of energy as a flare. Whether or not the star stayed intact for the duration of its death-spiral into the supermassive black hole it is unknown, but scientists have been working on a new model of a star orbiting a black hole weighing in at a few million solar masses (assuming the star can hold it together for that long).

The pancake effect of a star falling into the tidal radius of a black hole (J.-P. Luminet)

Matthieu Brassart and Jean-Pierre Luminet of the Observatoire de Paris-Meudon, France, are studying the effects of the tidal radius on a star orbiting close to a supermassive black hole. The tidal radius of a supermassive black hole is the distance at which gravity will have a far greater pull on the leading edge of the star than the following edge. This massive gravitational gradient causes the star to be stretched beyond recognition. What happens next is a little strange. In a matter of hours, the star will swing around the black hole, through the tidal radius, and out the other end. But according to the French scientists, the star that comes out isn’t the same as the star that went in. The star deformation is described in the accompanying diagram and detailed below:

  • (a)-(d): Tidal forces are weak and the star remains practically spherical.
  • (e)-(g): Star falls into the tidal radius. This is the point at which it is destined to be destroyed. It undergoes changes in its shape, first “cigar shaped”, then it gets squeezed as the tidal forces flatten the star in its orbital plane to the shape of a pancake. Detailed hydrodynamical simulations of shock wave dynamics have been carried out during this “crushing phase”.
  • (h): After swinging around the point of closest approach in its orbit (perihelion), the star rebounds, leaving the tidal radius and begins to expand. Leaving the black hole far behind, the star breaks up into clouds of gas.

As the star is dragged around the black hole in the “crushing phase” it is believed that the pressures will be so great on the deformed star that intense nuclear reactions will occur throughout, heating it up in the process. This research also suggests powerful shock waves will travel through the hot plasma. The shock waves would be powerful enough to produce a short (<0.1 second) blast of heat (>109 Kelvin) propagating from the star’s core to its deformed surface, possibly emitting a powerful X-ray flare or gamma-ray burst. Due to this intense heating, it seems possible that most of the stellar material will escape the black holes gravitational pull, but the star will never be the same again. It will be transformed into vast clouds of turbulent gas.

This situation wouldn’t be too hard to imagine when considering the dense stellar volume in galactic nuclei. In fact, Brassart and Luminet have estimated that there may be 0.00001 event per galaxy, and although this may seem low, future observatories such as the Large Synoptic Survey Telescope (LSST) may detect these explosions, possibly several per year as the Universe is transparent to hard X-ray and gamma-ray emissions.

Source: Science Daily

Posted on by Nancy Atkinson

Gravity Anomaly Challenges MESSENGER Mission

Scientists from the MESSENGER mission continue to analyze the data from the spacecraft’s first flyby of Mercury on January 14, 2008. Initial data about the planet’s gravity field grabbed the science team’s attention, as the actual gravity data differed from predictions based on the Mariner 10 flyby in 1975. Any unknowns in Mercury’s gravity will provide challenges for the spacecraft’s navigation during the next flyby in October, and especially when MESSENGER goes into orbit of Mercury in 2011. This in turn could affect quality and detail of science observations. “There indeed are residuals that we have not yet been able to explain fully,” said Ralph McNutt, MESSENGER Project Scientist. “While we believe we have resolved possible extraneous effects, we continue to work those as well.”

The new data about Mercury’s internal structure is different from what the scientists expected. McNutt said that while it was surprising that the tracking data did not fit all of their preconceived notions from Mariner 10, MESSENGER went much closer to Mercury than did Mariner, which could account for the differences in data. Scientists believe there may be a large concentration of mass (mascons) under Mercury’s surface about 10 degrees south of the equator at about 60 degrees longitude. A presentation by team member David Smith at the Lunar and Planetary conference in March showed that they were able to account for about 95% of the problem deviation using a single mass anomaly at that location.

“This also leads into the most important thing on flyby 2,” said McNutt, “as we will have closest approach on the other side of the planet, we will then be able to obtain a much better separation of global versus local (mascon) signatures. So we expect major advances in our understanding of the gravity field from the 2nd flyby as it will complement the information gleaned from the first.”

From MESSENGER Navigation Team Chief Ken Williams’ perspective, any new information and understanding of this issue is important. “We’re following very closely any developments in understanding the gravity field,” said Williams. “As we encounter Mercury each time, we’re trying to build up our knowledge of what the gravity field is going to be. It’s not critical that we know it in fine detail right now, but obviously when we settle into orbit we’re going to want to know a lot more about it because that will affect the design of the orbit trim maneuvers that we’ll have to do.”

McNutt said the initial the command loads for the second flyby are being delivered to Mission Operations this week.

But Williams said the first flyby provided good news as far as knowing Mercury’s actual location in space. “While we had a pretty good idea of Mercury’s ephemeris, that fact that it hadn’t been visited by a spacecraft for a long time, there was a chance it would be different than we thought,” said Williams. “We did some things with optical navigation as we were flying by and it confirmed that it was only 2 km away at most from the ephemerides that JPL publishes. That was a great relief. That takes away the uncertainty for future encounters.”

MESSENGER’s orbit around Mercury will be affected by another perturbation, known as third body gravity, from the Sun’s gravity field. At first this effect will draw MESSENGER away from Mercury, but later in the mission it will force the spacecraft towards the planet. Williams said one navigation analyst estimated that if the mission ended in 2012 and no further maneuvers were done by the spacecraft, MESSENGER would impact Mercury sometime in 2016.

McNutt was clearly pleased with the data from the first flyby, and looks forward to the second. “The first flyby provided humanity’s first closeup of 21% of Mercury’s surface as well as an amazing set of data on the Caloris basin. We have also made major advances in our understanding of Mercury’s exosphere, magnetosphere, and surface mineralogy. The second flyby will provide a similar close-up of another 33% of terra incognita, and only ~1% of Mercury will not have been viewed by a spacecraft when we enter orbit in 2011.”

Posted on by Nancy Atkinson

NASA Flips for Petaflops

NASA is collaborating with Intell and SGI to create one of the world’s fastest supercomputers whose power will be measured in petaflops. By 2009 the US space agency wants to develop a computational system that will be able to do 1,000 trillion calculations per second. And by 2012 it hopes to have boosted the power of this machine to 10 petaflops, to help with modelling and simulation. NASA’s Advanced Supercomputing Division is calling the new project Pleiades, and it will be installed at the Ames Research Center in California, the site of its current supercomputer, Columbia, pictured here. The new computer would put NASA on the list of the top five fastest number crunchers in the world.

“Throughout its history, NASA has sought to explore the most compelling questions about mankind, Earth, and the worlds that await our discovery,” said Robert “Bo” Ewald, chief executive officer of SGI. “These groundbreaking new systems powered by SGI and fueled by the latest multi-core Intel processors, offer a platform for new discoveries that will help us all achieve the most promising future for the human race. This effort is important to everyone on this planet.”

NASA uses its current supercomputer to examine the performance of hypersonic aircraft, simulate lander deployments and model fabrics for future spacesuits.

“This additional computational performance is necessary to help us achieve breakthrough scientific discoveries,” said Pete Worden, Director at Ames.

Currently, the most powerful supercomputer on Earth is BlueGene/L which has a top speed of 478.2 teraflops.

Columbia was turned on in 2004 and has a theoretical peak of 88.88 teraflops. This makes it the 20th most powerful supercomputer on the planet, according to the Top 500 Project which compiles a list of the relative performance of these machines.

Petaflop computers are expected to debut in the next release of the Top 500 list which is due in June.

Quasi-supercomputing, where multiple computers are used using the BOINC platform has already achieved petaflop status. Folding@home, reported nearly 1.3 Petaflops of processing power in late 2007.

The largest BOINC project, SETI@home, reported processing power of over 450 teraflops through almost 350,000 active computers.

Original News Sources: BBC, NASA

Posted on by Nancy Atkinson

Long-term Observations Reveal Patterns in Saturn’s Atmosphere

Reading something like this makes me hopeful that we’re no longer in the infant stage of our understanding of our solar system: we’ve been patient and observant while growing in our knowledge. Scientists have discovered a wave pattern, or oscillation, in Saturn’s atmosphere only visible from Earth every 15 years. This discovery was made only because we’ve been studying Saturn from ground based telescopes for about 22 years. Combined with the Cassini spacecraft’s observations of temperature changes in the giant planet’s atmosphere over time, we’re gaining a better understanding of Saturn and discovering not only how unique it is, but also that Saturn has something in common with Earth. Our own planet has these oscillations too, and so does Jupiter. “You could only make this discovery by observing Saturn over a long period of time,” said Glenn Orton, of JPL, lead author of the ground-based study. “It’s like putting together 22 years worth of puzzle pieces, collected by a hugely rewarding collaboration of students and scientists from around the world on various telescopes.”

The image above shows a pattern ripples back and forth like a wave within Saturn’s upper atmosphere. In this region, temperatures switch from one altitude to the next in a candy cane-like, striped, hot-cold pattern. The temperature “snapshot” shown in these two images captures two different phases of this wave oscillation: the temperature at Saturn’s equator switches from hot to cold, and temperatures on either side of the equator switch from cold to hot every Saturn half-year.

The image on the left was taken in 1997 and shows the temperature at the equator is colder than the temperature at 13 degrees south latitude. Conversely, the image on the right taken in 2006 shows the temperature at the equator is warmer.

Results from Cassini’s infrared camera indicate that Saturn’s wave pattern is similar to a pattern found in Earth’s upper atmosphere, which takes about two years. A similar pattern on Jupiter takes more than four Earth years. The new Saturn findings add a common link to the three planets.

Cassini scientists hope to find out why this phenomenon on Saturn changes with the seasons, and why the temperature switchover happens when the sun is directly over Saturn’s equator.

Original News Source: JPL Press Release

Posted on by Fraser Cain

Carnival of Space #53

This week, the Carnival of Space is hosted by the Space Cynics. A big thanks to them for stepping in at the last minute to host this week’s edition.

Click here to read the Carnival of Space #53

And if you’re interested in looking back, here’s an archive to all the past carnivals of space. If you’ve got a space-related blog, you should really join the carnival. Just email an entry to [email protected], and the next host will link to it. It will help get awareness out there about your writing, help you meet others in the space community – and community is what blogging is all about. And if you really want to help out, let me know if you can be a host, and I’ll schedule you into the calendar.

Finally, if you run a space-related blog, please post a link to the Carnival of Space. Help us get the word out.

Posted on by Nancy Atkinson

Popular Space Elevator Video Not “News,” says LiftPort Founder

An online video that’s been circulating like wildfire on the internet recently is actually almost two years old, says Michael Laine, founder of LiftPort, a company looking to develop a space elevator. The video was taken in the fall of 2006, at least 20 months ago.

The video has been downloaded over 200,000 times in the past few days, and has been extremely popular on sites like Digg. “I find the whole thing kind of a farce, actually,” said Laine. “I’m glad people are seeing it and commenting on it, but if someone thinks this is news, its not.”

The only reason Laine could site for a possible resurgence of this video is that last Friday, the Conan O’Brien show featured a guest talking about space elevators. Laine wonders if that led to people doing searches about the subject, finding this old video on You Tube, and re-posting it as “new.” Laine says LiftPort has received slightly more email than normal the past couple of days, but until now no one has contacted him to check on the authenticity or timing of the video.

“Everything in it is true, except the timing is strange,” said Laine. “Those are my quotes, (listed along with the video) but I don’t know how someone obtained them, and got that wording. What’s ironic is that we’ve done a lot of experiments since then. That specific test was supposed to be a mile high test, but we had problems with the ribbon snapping. The FAA required that we put markers on it, and the acetone used to mark it weakened the ribbon substantially. The test turned out to be 1,000 feet. We actually were very happy about the test, although we almost lost the ribbon.”

Laine was especially surprise to hear of this new interest in Liftport, since the company has gone through some hard times over the past year, losing investors, a building, and other support. Laine said he will have some positive news to report soon, so stay tuned.

And OK, here’s the video. (You Tube’s version, not LiveLeak’s!) It is pretty amazing.

Click here for more information about LiftPort.

Posted on by Fraser Cain

How Far is Mercury from Earth?

Orbit of Mercury

Although Galileo wasn’t able to see the phases of Mercury (like the phases of Venus and the Moon) with his first crude telescope, the astronomers that carried on his discoveries did. This was powerful evidence that both Mercury and Earth are orbiting the Sun.

You can also check out these amazing books for more information about the planet Mercury.

Since Mercury orbits the Sun, and it follows a very elliptical path on its journey around the Sun, our two planets can vary their distance significantly.

When Mercury is at its closest point to Earth, astronomers call this opposition (from the point of view of Mercury). This would happen when Mercury was at its furthest from the Sun, and Earth is at its closest. When this happens, Mercury and Earth would be separated by only 77 million km (48 million miles).

Their maximum distance occur when Earth is at its furthest point from the Sun, and Mercury is at its maximum on the other side of the Sun. The three objects then line up perfectly. At this point, Mercury and Earth can be 222 million km (138 million miles) apart.

Distancia desde la Tierra a Mercurio

Posted on by Jerry Coffey

How Far is Venus from Earth?

The are varying numbers for the Venus distance from Earth. Each number depends on the relative position of each planet in its elliptical orbit. The point when the planets are at their closest approach to each other is called opposition. The distance between the planets can even vary at different oppositions. The closest possible opposition distance between Earth and Venus is 38 million kilometers. This is the closest that any planet comes to Earth.

The farthest that Venus ever gets from Earth is 261 million km. The means that the Venus distance from Earth can vary by an incredible 223 million km. While that seems like an amazing distance, it is nothing compared to the numbers attributed to other planets. Try to imagine how far it is between Earth and Neptune. Here is a link that tells you how to figure those distances out.

The relative proximity of Venus helps to explain why it is the second brightest object in the night sky. The planet has an apparent magnitude of about -4.9 at its brightest. It can also completely disappear from the night sky when it is at its most distant, because the Sun is between it and the Earth. The planet’s apparent magnitude is also helped by the reflectivity of the sulfuric acid clouds that dominate its atmosphere. The clouds reflect a great deal of visible light, increasing the planet’s albedo and making it more readily seen.

Venus will periodically pass across the face of the sun. This is called a transit. These transits of Venus occur in pairs with more than a century separating each pair. Since the advent of the telescope, transits have been observed in 1631, 1639; 1761, 1769; and 1874, 1882. the most recent occurred on June 8, 2004. The second in this pair will occur on June 6, 2012, so mark your calenders and prepare your telescopes. The planet can also be seen to go through phases much like the Moon when you observe it through powerful binoculars or small telescopes.

Venus is always brighter than any star. It is at its brightest when the Venus distance from Earth is the smallest. The planet can be easy to see when the Sun is low on the horizon, it always lies about 47° from the Sun. The planet orbits faster than the Earth, so overtakes it every 584 days. When this happens Venus is more easily seen in the morning, just after sunrise. Hopefully, you have found quite a bit of useful information here.

We have written many articles about Venus for Universe Today. Here are some interesting facts about Venus, and here’s an article about Venus compared to Earth.

If you’d like more information 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 entire episode of Astronomy Cast all about Venus. Listen here, Episode 50: Venus.

References:
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Venus&Display=OverviewLong
http://curious.astro.cornell.edu/question.php?number=564