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Scott Kardel from the Palomar Observatory just posted something extremely cool on his Palomar Skies website. Back in 2001, a group of astronomers used the 200-inch Hale Telescope equipped with adaptive optics to observe Saturn’s moon Titan pass in front of a binary star system. The binary stars are separated in the sky by just 1.5 arc seconds, but because of the fantastic resolving power of the Hale and its adaptive optics, visible in the image above is the light of the star nearest to Titan being refracted by Titan’s dense atmosphere. As Scott said, such events are rare but valuable. Mike Brown (of Eris fame) was among the astronomers and on Twitter today, he linked to a video the team created from their observations, which is just awesome. Not only did they see the occultation, but they also found out that Titan has jet stream-like winds in its atmosphere. Watch the movie, (or see below, someone has now YouTubed it) and then read their paper about the event!
How cool is that. Amazing that you can make out the refracted images of the two stars on the limb throughout the occultation (the first star along the ‘top’ of Titan, the second star beneath). The paper describes the phenomena as “a limited form of central flash”. To an old occultation and graze observer, that was my first impression. Some fantastic work.
I see from the paper (Fig. 2) that two images of the stars are visible during Titan occultation, one image being brighter due to the path of the star behind Titan. A cool demonstration of atmospheric refraction.
W-o-w!
And both Venus and Titan are putative atmospheric superrotators I take it (peeked in Wikipedia). Looks like it’s the oceans/plate tectonics of Earth breaking up atmospheric cells, and perhaps the faster rotation, that makes our current climate mild in comparison!? Imagine that.
[If it’s the rotation, the Moon slowing us down over time is presumably _not_ the boon the rare earth ideas once said.]
*gasps, yelps and shouts*
This is just too good. I could actually see the second star’s two images!
Thanks for sharing!
My google fu gives the following definition and picture of a central flash.
“A light curve is the brightness or intensity of light plotted against time on a graph. As Titan passed in front of the star, the light seen from the two objects decreased in intensity. If the center of Titan passes close enough to the line of sight from the star to the observer, just at the midpoint of the occultation, a small peak of light called a central flash is observed. The central flash is starlight refracted by Titan’s atmosphere. The atmosphere of Titan acts as a lens. This central flash helps astronomers measure the shape of Titan’s atmosphere […]”
Looking at the graph, the flash is centered in the intensity graph; it is the context of the flash itself. I’m fairly certain that is the intended definition, found a similar description of a Neptune occultation without any mentioning of “the center” of the occulting body. Hopefully the experts will correct my false guesses.
That was cool. When titan was right in between the stars it eminded me of Galileo’s drawings of Saturn when he did not understand what he was seeing in the rings.
Image:
http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap12/FG12_10.jpg
What is central flash?
The flash along the atmosphere was amazing and I had to pause the video as Titan was in the middle, what a image.
That’s pretty badass.