Slashdot Mirror
Looking Directly at Extrasolar Planets
D2Deek writes "Science Daily is reporting on a new device called an Optical Vortex Coronagraph that's been invented to directly image planets orbiting other stars by using a special lens that "spins out" the light from the star leaving only the reflected light from the planet." I just can't imagine trying to clean a lens shaped like a giant corkscrew.
Do not look directly at extrasolar planets with remaining good eye.
Dark Reflection
This is actually more about the angle of light, say I want to capture all light in a very tight .005% angle. Unfortunatly there is a sun at the very very edge of my shot. Even though its technically out of the angle of my shot with conventional lenses the sun will glare through. This technology allows light at the edges of the lense to be spun off. It really has nothing to do with intensity.
Is that anything like the Total Perspective Vortex ??
try { do() || do_not(); } catch (JediException err) { yoda(err); }
A new optical device might allow astronomers to view extrasolar planets directly without the annoying glare of the parent star. It would do this by "nulling" out the light of the parent star by exploiting its wave nature, leaving the reflected light from the nearby planet to be observed in space-based detectors.
About ten years ago, the presence of planets around stars other than our sun was first deduced by the very tiny wobble in the star's spectrum of light imposed by the mutual tug between the star and its satellite. Since then, more than 100 extrasolar planets have been detected in this way. Also, in a few cases the slight diminution in the star's radiation caused by the transit of the planet across in front of the star has been observed. Many astronomers would, however, like to view the planet directly, a difficult thing to do.
Seeing the planet next to its bright star has been compared to trying to discern, from a hundred meters away, the light of a match held up next to the glare of an automobile's headlight. The approach taken by Grover Swartzlander and his colleagues at the University of Arizona is to eliminate the star's light by sending it through a special helical-shaped mask, a sort of lens whose geometry resembles that of a spiral staircase turned on its side.
The process works in the following way: light passing through the thicker and central part of the mask is slowed down. Because of the graduated shape of the glass, an "optical vortex" is created: the light coming along the axis of the mask is, in effect, spun out of the image. It is nulled, as if an opaque mask had been placed across the image of the star, but leaving the light from the nearby planet unaffected.
The idea of an optical vortex has been around for many years, but it has never been applied to astronomy before. In lab trials of the optical vortex mask, light from mock stars has been reduced by factors of 100 to 1000, while light from a nearby "planet" was unaffected (see figure).
Attaching their device to a telescope on Mt. Lemon outside Tucson, Arizona, the researchers took pictures of Saturn and its nearby rings to demonstrate the ease of integrating the mask into telescopic imaging system. This is, according to Swartzlander (520-626-3723, grovers@optics.arizona.edu), a more practical technique than merely attempting to cover the star's image, as is done in coronagraphs, devices for observing our sun's corona by masking out the disk of the sun. It could fully come into its own on a project like the Terrestrial Planet Finder, or TPF, a proposed orbiting telescope to be developed over the coming decade and designed to image exoplanets.
Foo et al., Optics Letters, 15 December 2005 Summary of articles related to optical vortex on Swartzlander's Web page
Someone more patient than I can put in the links to the figures. See http://aip.org/pnu/2005/755.html for everything.
I just can't imagine trying to clean a lens shaped like a giant corkscrew.
Just run a lint-free Debian logo through it a couple of times.
"I'd rather be a lightning rod than a seismometer." -Ken Kesey
The submitter mentioned cleaning lenses and other optical equipment. I want to comment that that's a very tricky thing. Most optical manuals just say: Do not attempt to clean!! Some recent developments are in the area of strip coatings (you pour a polymer over the surface and peel it off to remove dirt without damaging the optics). This has been tried since the early XX century but only recently has became practical. Here's a link to a group that developed a sucessful formula for that process: http://www.uwplatt.edu/~hamiltoj/
"Destroy science and religion. Science would re-emerge exactly the same; but not religion." - Penn Jillette, paraphrased
It's worth RTFA just to see a reference to "Foo et al."
(The full paper title is "Optical Vortex Coronagraph" by Gregory Foo, David M. Palacios, Grover A. Swartzlander Jr., College of Optical Sciences, University of Arizona).
"How to Do Nothing," kids activities, back in print!
Your point is valid. A better analogy would be more like a mirror the size of an eraser, reflecting light from a match held a few hundred meters away, in front of a car headlight.
(Actually, I don't know if the proportions are even remotely close, but meh.)
I tend to think it's quite appropriate. Granted, in the strictist of senses, yes a planet reflect the star's light while a match creates its own. But from a analogical sense, it works. The brightness of the light from the match is a fraction of the light coming out of the headlight, just as the light reflected towards us from the planet is many times dimmer than the starlight itself. When applied to very large planets, which are the only extra-solar ones we've discovered so far, the size comparison works as well. Plus who's to say the planet is not a dim-light emitting gas giant? ;)
The point is, the analogy does get across the difficulty of this acheivement quite well, even moreso when you don't knitpick it to oblivion.
"This is Zombo Com, and welcome to you who have come to Zombo Com" - www.zombo.com
"As Gilman looked into the Optical Vortex Coronagraph at the extrasolar planet, he became conscious of some formless alien presence watching him with horrible intentness. He felt entangled with something -- something which was not in the telescope, but which had looked through it at him. Something which would ceaselessly follow him.
"Cautious investigators will hesitate to challenge the common belief that Gilman was killed by lightning, or by some profound nervous shock derived from an electrical discharge. Archaeologists and astronomers, however, are still trying to explain the bizarre designs impressed on the special helical-shaped mask, whose inner side bore ominous stains."
Apparently all the work so far is only computer simulations. There are some serious problems to overcome before this could be a practical system. The author states:
"These calculations assume no aberrations or other scattering sources, and they assume the vortex mask can be made achromatic."
http://www.u.arizona.edu/~grovers/ovc.html
In other words, the lens material is made from unobtanium and the rest of the system has to be perfect. The author certainly knows this will never happen.
Mike
You wont be able to see any surface details, but the point, for those who don't already know, is that if you can look at just the light that's reflected, then you can run that light through a spectroscope. If you see in the spectroscope that there is free oxygen in the atmosphere, then you've probably found life. See, free oxygen (O2) doesn't occur anywhere in nature - except where it's created by life. So, if you find lots of O2 in the atmosphere, you've found a living planet (and a reason to build daedelus)
Your math is off.
15years*300000km/s*86400s*364.25days = 14162040000000km, not 472068000km
Thus, the angle comes to 5.63e-7 degrees, or 0.002 arcseconds
The 472,068,000 doesn't include the 300,000km/s. The real number would be 142,009,200,000,000. (also a year is 365.25 days, but the 15 light-year measurement is much less accurate than that I suspect) The page you point to says the planet's average orbit is 0.2 times the earth-sun distance, about 31.5 million km. That gives an angular distance between the star and planet of about 0.0000127 degrees, or 0.045 arcseconds. The hubble can resolve about 0.07 arcseconds, if we can separate the glare from the star bleeding over, then we are close.
Can't image things until you can find them. Can't find them if the starlight is making it impossible to discern the planet.
m0nstr42.blogspot.com
This is why you're taught in courses on physics how to estimate things like the weight of the pyramids or the capacitance of clouds (well we were). So you aren't just a slave to your calculator and can actually detect when a number is BS.