Seeing Pluto

[Loren Booda]

Stars twinkle because our atmosphere's turbulence causes these point-like bodies to scintillate, whereas planets supposedly appear large enough not to twinkle. Is Pluto (a distant and small planetoid) enough of a point to twinkle as seen from Earth?

[DaveC426913]

Stars twinkle because our atmosphere's turbulence causes these point-like bodies to scintillate, whereas planets supposedly appear large enough not to twinkle. Is Pluto (a distant and small planetoid) enough of a point to twinkle as seen from Earth?

Pluto is not visible to the naked eye from Earth. At a mag of 13, it is orders of magnitude below naked eye visible (~6.6) and below any other stars you will see.

[Loren Booda]

By "seeing" I was trying to refer to the term for atmospheric scintillation (twinkling), whether observed by telescope or naked eye. Let me rephrase: is it possible to encounter significant "twinkling" when observing Pluto from Earth?

[russ_watters]

Yes: the more you magnify an object, the more atmospheric scintillation comes into play. And Pluto is so small, it would barely be more than a point of light in even a very large amateur telescope.

[twofish-quant]

Here are some pictures of Pluto "twinkling"

http://articles.adsabs.harvard.edu//full/1987A%26A...174..295B/0000297.000.html

What you can do with Pluto is to take lots of short observation of the planet twinkling, and then run them through some mathematics to get the shape of Pluto and its moon Charon.

[Loren Booda]

Here are some pictures of Pluto "twinkling"

http://articles.adsabs.harvard.edu//full/1987A%26A...174..295B/0000297.000.html

What you can do with Pluto is to take lots of short observation of the planet twinkling, and then run them through some mathematics to get the shape of Pluto and its moon Charon.Why does it appear that there are two images of Charon in the photos - is that due to diffraction?

[mgb_phys]

Speckle is a technique where you take an image of the pupil plane (essentialy the fourier transform of the image) and then create an image by fitting an interative model to the data.
One of the side effects of the process is that you have a symmetric image because there aren't enough degrees of freedom in the data to decide which is correct.

Also the point of speckle is to remove atmopsheric twinkle effects - so it's a bit pointless in this discussion. Pluto would twinkle like a star through a telescope powerfull enough to see it. Planets don't twinkle because they are several times bigger than the size of the atmospheric distortion (1arc sec), pluto is smaller than this

[russ_watters]

Planets don't twinkle because they are several times bigger than the size of the atmospheric distortion (1arc sec), pluto is smaller than this For everyone's info, that's probably a good number for an average day, but it can be worse or better, probably on a range of 0.1 to 2 arcsec 90% of the time.

The angular diameters of a few objects as viewed from Earth:
Andromeda Galaxy: 11,400 arcsec
Sun/Moon: 1,800 arcsec
Jupiter: 40 arcsec
Europa: 1.0 arcsec
Pluto: 0.10 arcsec (looked it up - that's actually bigger than I expected)
Betelgeus: 0.050 arcsec

[Vanadium 50]

Russ, what's the star with the largest angular diameter as seen from earth? Gamma Crucis perhaps? It's rather large and quiet close.

[mgb_phys]

In the northern hemisphere it's probably Betelgues. We took images of it using a speckle-like technique that resolve bright spots on the star

[ideasrule]

In the southern hemisphere it's R Doradus, with an angular diameter of 0.06 arcsec. For many reasons, R Doradus is nowhere as interesting as Betelgeuse and is relatively obscure.

[twofish-quant]

The mirror image comes as a result of the mathematics that the use to get the images from the speckles. Unfortunately, I'm not familiar enough with the math to know why that happens and would welcome someone that knows more about interferometry to chime in.

[mgb_phys]

Basically because you don't have any information on the absolute phase so the reconstruction algorithm has two (- and +) solutions.

[russ_watters]

Russ, what's the star with the largest angular diameter as seen from earth? Gamma Crucis perhaps? It's rather large and quiet close. Don't actually know, sorry - I just pulled a few out of the air, plus looked a wiki for the question.