APOD: At the Limit of Diffraction (2015 May 07)

[Craine]

You guys realize that when I hold a camera all I do is point-n-click right?
k...not entirely true. But almost.
Once I had to write some code that would take images of really blurry text and try and reconstruct the text. So yeah...I am in kindergarten as far as manipulating image data goes.

Well, now you know what to expect next time you ask a bunch of imaging nerds a question. Give yourself some credit, though. Kindergarten is using a web app to apply meme text to cat pics.

Hey, I am learning stuff today. I call it a win.

[SarbaGuha]

Though I am not one who thought they are 4-inches apart...... ......the question did come up in my mind as to how far apart they really are. Do you know? Thanks.

The two orbit each other with an 80 year period, and an orbit of fairly high eccentricity (0.5), so the distance between them varies quite a bit, from about 11 AU to about 36 AU. And from our perspective looking at this system somewhat from on-edge, the apparent separation range is even greater, from 2 to 22 arcseconds.

Thanks Chris for your answer. Just noticed it.

[LocalColor]

Here's a lecture by Laird Close where he talks about this system and how he hopes this technology will ultimately enable us to image light coming off of exoplanets:

https://www.youtube.com/watch?v=SVeTncz ... e=youtu.be

Some of the talking points from this lecture:
- By analyzing Kepler data and extrapolating for what we believe the typical exoplanet population is like in the Milky Way, as many as 20% of stars in the MW may well have an Earthlike world in the habitable zone... that's one in five stars.
- NASA is working on a concept for a next generation large space telescope after James Webb whose goal is to be able to image Earthlike worlds in the habitable zone of sunlike stars. This will enable atmospheric analysis by means of spectroscopy, which would enable us to detect methane and oxygen in planet atmospheres. A detection of both of these gases is a strong indicator of a biosphere.

Upshot: We could have evidence for extraterrestrial life within the next couple decades. Really exciting!

This is from a series of lectures at University of Arizona covering various new developments in Astrobiology. The whole series was fascinating:

http://cos.arizona.edu/connections/life-in-the-universe

-s

Thank you for the links Spif, added to our "lectures to watch" - this will be a nice addition to the astrobiology course we watched last year from Coursera.org.

[addseo1115]

Nice to see your wonderful discussion. Thanks for sharing.

[yaranoff@gmail.com]

I wonder when we'll have this method available on commercial high end telescopes (from 10" and up). It would be great to view the stars without atmospheric distortion!

[Chris Peterson]

I wonder when we'll have this method available on commercial high end telescopes (from 10" and up). It would be great to view the stars without atmospheric distortion!

There are many reasons not to expect this.

First, it takes about 250 mm of aperture (in some cases more) to sample a column of sky. That's aperture not devoted to the normal image plane. In other words, you need to siphon off a lot of light to analyze the seeing, so you need a large aperture to begin with.

Second, you either need a bright reference star very close to your target (which demands a large aperture), or you need to create one with a powerful laser (which requires licensing that your average backyard astronomer will not obtain). The correction for seeing is only accurate within a few arcminutes (or even arcseconds) of the reference object. Wide field corrected fields require even more reference objects (typically achieved with multiple laser guide points).

The only practical active optics systems for amateur class telescopes (less than a meter) are lowest order- just tip and tilt to correct drift of the entire field. And it turns out that there isn't a lot of that except (somewhat paradoxically) under very good seeing conditions. Most of the seeing distortion is higher order, affecting different parts of the field differently. People have made tip/tilt correctors for amateur scopes. They aren't useful for visual observing at all, because your eye already corrects for that kind of motion when you're at the eyepiece. They can improve images, however, but most of the correction is actually for tracking errors of the mount, not motion of the air above it (except, as previously noted, when imaging under already very good seeing).