From Dr. Tony Phillips Science at NASA
When Venus transits the sun on June 5th and 6th, an armada of spacecraft and ground-based telescopes will be on the lookout for something elusive and, until recently, unexpected: The Arc of Venus.
“I was flabbergasted when I first saw it during the 2004 transit,” recalls astronomy professor Jay Pasachoff of Williams College. “A bright, glowing rim appeared around the edge of Venus soon after it began to move into the sun.”
For a brief instant, the planet had turned into a “ring of fire.”
Researchers now understand what happened. Backlit by the sun, Venus’s atmosphere refracted sunlight passing through layers of air above the planet’s cloudtops, creating an arc of light that was visible in backyard telescopes and spacecraft alike.
It turns out, researchers can learn a lot about Venus by observing the arc. Indeed, it touches on some of the deepest mysteries of the second planet.
› View larger
The arc of Venus photographed in 2004 by Riccardo Robitschek and Giovanni Maria
Caglieris of Milan, Italy. “We do not understand why our sister planet’s atmosphere evolved to be so different than Earth’s,” explains planetary scientist Thomas Widemann of the Observatoire de Paris.
Earth and Venus are similar distances from the sun, are made of the same basic materials, and are almost perfect twins in terms of size. Yet the two planets are wrapped in stunningly dissimilar blankets of air. Venus’s atmosphere is almost 100 times more massive than Earth’s and consists mainly of CO2, a greenhouse gas that raises the surface temperature to almost 900°F. Clouds of sulfuric acid tower 14 miles high and whip around the planet as fast as 220 mph. A human being transported to this hellish environment would be crushed, suffocate, desiccate, and possibly ignite.
For the most part, planetary scientists have no idea how Venus turned out this way.
“Our models and tools cannot fully explain Venus, which means we lack the tools for understanding our own planet,” points out Widemann. “Caring about Venus is caring about ourselves.”
One of the biggest mysteries of Venus is super-rotation. The whole atmosphere circles the planet in just four Earth days, much faster than the planet’s spin period of 243 days. “The dynamics of super-rotation are still a puzzle despite a wealth of data from landmark missions such as NASA’s Pioneer Venus, Russia’s Venera and VEGA missions, NASA’s Magellan and more recently ESA’s Venus Express.”
› View larger The arc of Venus as seen by NASA’s TRACE spacecraft in 2004. Credit: NASA/Trace/LMSAL
This is where the Arc of Venus comes in. The brightness of the arc reveals the temperature and density structure of Venus’s middle atmosphere, or “mesosphere,” where the sunlight is refracted. According to some models, the mesosphere is key to the physics of super-rotation. By analyzing the lightcurve of the arc, researchers can figure out the temperature and density of this critical layer from pole to pole.
When the arc appeared in 2004, the apparition took astronomers by surprise; as a result, their observations were not optimized to capture and analyze the fast-changing ring of light.
This time, however, they are ready. Together, Pasachoff and Widemann have organized a worldwide effort to monitor the phenomenon on June 5th, 2012. “We’re going to observe the arc using 9 coronagraphs spaced around the world,” says Pasachoff. “Observing sites include Haleakala, Big Bear, and Sacramento Peak. Japan’s Hinode spacecraft and NASA’s Solar Dynamics Observatory will also be gathering data.”
Pasachoff has some advice for amateur astronomers who wish to observe the arc. “The best times to look are ingress and egress–that is, when the disk of Venus is entering and exiting the sun. Ingress is between 22:09 and 22:27 UT on June 5th; egress occurs between 04:32 and 04:50 UT. Be sure your telescope is safely filtered. Both white light and H-alpha filters might possibly show the arc.”
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Could the NASA budget extend toward buying them a new tape measure, preferably one with inches and centimeters. This may increase their awareness distance.
Owen;
The comment with the pressure tanks is here:
http://wattsupwiththat.com/2012/06/05/transit-of-venus-today-may-reveal-the-mysterious-arc-of-venus/#comment-1002039
And it’s 2 Venus atmospheres, or almost 200ATM, not 2.
Ellen says:
June 5, 2012 at 9:20 am
Ignite? Not in a CO2 atmosphere!
Pyrolysis is a more exact term for what would occur. You’d end up as charcoal, most likely.
The atmosphere of Earth 4Ba ago was like that of Venus today. It was hot but Earth had water which changed the atmospheric chemistry by dissolving lots of that gas into the water so lowering the surface density and temperature. Remember the bulk of the atmosphere had yet to outgas from the rocks of the mantle at this time. Temperature was higher than today but low enough to encourage simple carbon molecules to recombine to form more complex ones, something carbon is very good at. This took about 1Ba which lead to cyanobacteria which altered the CO2 to O2 and growth. The rest is history.
Brian H: Thanks for the link. My statement is still true however and even more so at the higher pressure. The tanks would have given off very considerable heat when the gas was compressed.
Owen in GA says:
June 5, 2012 at 2:15 pm
“Unfortunately we are going to be rained out and not get to see it. We were going to set up all the university’s solar telescopes to view it too. However we need the rain more than the view.
Jim G: is .67AU similar to 1AU? I suppose if you round to the nearest whole number it is. The rest is good.”
Owen,
It is. You need to think like an astronomer. Most objects studied are tens, hundreds, thousands, millions or billions of light years away. A few are AU’s away so Venus is about the same distatnce from the Sun as is the Earth when thinking in these terms. Much more was made of this comment than it was worth. The CO2 greenhouse BS was another story, however. Also, at 100 atmospheres and no O2 a person would not only not ignite but would be crushed. Been a long time since my physics class that covered gas temperature and pressure but I would agree with those indicating that such pressures would cause big heat.
true, but being more of an applied electronics guy I think of things in percentage change and 30% can be large (or not depending on circuit tolerances. We’ve had on and off vary by about that much in some circuits and still work. Much more and 1/0 becomes ambiguous = bad.) In computational physics I did a three body problem simulation in which a 1% error was too big to tolerate, so I guess it depends on your starting view and the problem you are solving. I was doing a Goldilocks simulation study on a planet in a binary star system, and 30% error in either irradiance or position would have fried it. (Turns out there are only a few configurations of close in binaries that are stable for a planet in the Goldilocks zone, and they are precarious.)
Jim G says:
June 6, 2012 at 11:44 am
No, I think the objections are not only valid but necessary in order to counter the prevailing but misleading popular misconception that “Venus is Earth’s twin.”
.
And the objection to “ignite” still holds. What is the oxidant? No oxygen, remember.
Obviously some strange usage of the word “similar” I hadn’t previously been aware of.
h/t Arthur Dent (via Douglas Adams)
Ah, so 100ly is a similar distance to 66.6ly. Makes perfect [non]sense.
Jeff;
From the POVs of galactic clusters or quarks (or even Pluto), very similar indeed; almost indistinguishable.
Jeff Alberts says:
June 7, 2012 at 12:55 pm
It is. You need to think like an astronomer. Most objects studied are tens, hundreds, thousands, millions or billions of light years away. A few are AU’s away so Venus is about the same distatnce from the Sun as is the Earth when thinking in these terms.
“Ah, so 100ly is a similar distance to 66.6ly. Makes perfect [non]sense”
No. But when thinking in LY’s the difference between 1AU and .67AU is miniscule.
–sorry for the dupe Mods; flubbed tags–
Brian H says:
June 8, 2012 at 5:51 am
and Jim G says:
June 8, 2012 at 7:54 am
Conspicuous by its absence in these arguments is any notion of scale.
Where I went to school, answers that were off by 30% were not likely to pass. We’re focused on a single star, not the entire galaxy or cosmos.
Discussion of terrestrials planets in the Solar System takes place within the reference frame of the orbit of Mars. On that scale, 25 million miles is highly significant, and the respective orbits of Venus and Earth must be characterized as “dissimilar,” since one is significantly closer to the Sun than the other.
But the Earth and the Moon can be said to have similar orbits around the Sun in terms of distance even though the Moon’s orbit is sorta wobbly in its path.
If an astronomer is thinking in lightyears when referring to an AU scale, he should turn in his astronomer badge. Your argument is extremely silly.