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Yul
2003-Feb-28, 10:17 PM
I believe this has been asked before, but can you give me an update: has any star yet been photographed with the new telescopes that shows a star (apart from the Sun) with a resolvable disc, as opposed to a pin-point source of light? If so, exactly which star? Alpha Centauri?

R.A.F.
2003-Feb-28, 10:26 PM
I thought I saw a picture of Betelgeuse that showed a disk, but I'm not sure where.

Colt
2003-Feb-28, 10:39 PM
I would think that if we were able to resolve a disc of a nearby star then we would be able to see its planets, maybe.-Colt

R.A.F.
2003-Feb-28, 11:02 PM
In this case, I'm as fuzzy about my facts as I am with my grammar...


On 2003-02-28 17:26, R.A.F. wrote:
...showed a disk...


/phpBB/images/smiles/icon_biggrin.gif

Zathras
2003-Feb-28, 11:03 PM
On 2003-02-28 17:39, Colt wrote:
I would think that if we were able to resolve a disc of a nearby star then we would be able to see its planets, maybe.-Colt

The problem with observing planets is that they would give off so much light themeselves that we just cannot see it. Perhaps if we saw the planet pass in front of the star somehow...

SiriMurthy
2003-Feb-28, 11:12 PM
I don't think that we have visually observed any extrasolar planets so far. We only have concluded the presence of planets around stars other than Sun by observing either the wobble in star's movements or increases and decreases in it's brightness.

With the technology we have I am not sure we can photograph an extrasolar planet.

I may be wrong. Please correct me if I am.

Thanks.

Rift
2003-Feb-28, 11:20 PM
We've resolved the disk of Betelgeuse quite some time ago. A quick web search came up with this http://www.mrao.cam.ac.uk/telescopes/coast/betel.html

If you are talking about planets, that's a different story, and I'm not sure if we have or not...

Zap
2003-Feb-28, 11:26 PM
To my understanding, we have not ever visually seen an extrasolar planet. Perhaps eventually, within the next 20 years or so, we will have the technology to do so. I can't wait until we start finding Earth-sized planets around other stars. Heck before we know it we'll be looking for extrasolar moons.

R.A.F.
2003-Feb-28, 11:31 PM
Rift, thanks for the link...good to know I'm not totally insane. /phpBB/images/smiles/icon_biggrin.gif

SiriMurthy
2003-Feb-28, 11:32 PM
Heck before we know it we'll be looking for extrasolar moons.


There you go. That is the attitude I like.

Tim Thompson
2003-Mar-01, 01:48 AM
R.A.F.: I thought I saw a picture of Betelgeuse that showed a disk, but I'm not sure where.

You are almost certainly thinking of this 1996 image of Betelgeuse from the Hubble Space Telescope: Hubble Space Telescope Captures First Direct Image of a Star (http://hubblesite.org/newscenter/archive/1996/04/). Rift linked to some IR images, but I think the HST image is optical.

Betelgeuse (http://www.aavso.org/vstar/vsotm/1200.stm) is a red supergiant, both large enough (about 1500 solar diameters) & near enough (about 425 light years) to present the largest apparent disk. It's apparent angular diameter was measured at 0.044 arcseconds by Michelson & Pease, with an interferometer attached to the 100-inch telescope on Mt. Wilson, in 1920 (Measurement of the diameter of alpha Orionis with the interferometer (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1921ApJ....53..249M&db_key=AST&high=3cf96e067128335), A.A. Michelson & F.G. Pease, Astrophysical Journal 53, 249-259, 1921). It has been measured several times since then (it is wavelength dependent, since the star has such a distended outer atmosphere).

So far as I know, only Betelgeuse has had it's disc imaged directly, without an interferometer. But at leas a few other stars have now had their angular diameters measured with the current suite of optical interferometers that are just starting to work.

No extrasolar planets have been imaged directly. Most have been detected by virtue of their affect on the apparent radial velocities of the parent star. But one, or maybe two, has/have been detected photometrically, by passing between us & the parent star.

tracer
2003-Mar-01, 02:54 AM
My copies of Theodore P. Snow's Essentials of the Dynamic Universe 1st Edition shows a false-color image of the surface of Betelgeuse taken with (I believe) ground-based speckle interferometry.

Since this book was published in 1983, the image had to be at least that old.

Rift
2003-Mar-01, 05:21 AM
You are almost certainly thinking of this 1996 image of Betelgeuse from the Hubble Space Telescope: Hubble Space Telescope Captures First Direct Image of a Star (http://hubblesite.org/newscenter/archive/1996/04/). Rift linked to some IR images, but I think the HST image is optical.



COOOOOL. I didn't realize we had actual optical images of the disk, that's awesome.

I remember seeing an IR image in grade school, so we've been able to resolve it that way for a loooong time. lol

But having an optical image of it is really neat.

_________________
"Ignorance has caused more calamity than malignity" H.G. Wells

<font size=-1>[ This Message was edited by: Rift on 2003-03-01 00:25 ]</font>

Glutomoto
2003-Mar-01, 07:50 AM
http://antwrp.gsfc.nasa.gov/apod/image/0007/hd12545_noao.jpg

This is NOT a direct image of another star, but still impressive, and a link to how they did it.
To observe spots on the surfaces of other stars, astronomers need to "resolve" the stellar disk. This cannot be done directly with the largest telescopes even planned, but Doppler imaging can be used to obtain a map of inhomogeneities on a star's surface. The principle is similar to medical tomography, but instead of a scanner rotating around a fixed object, a rotating star is observed with a fixed telescope. (http://www.noao.edu/noao/noaonews/dec99/node2.html)

Yul
2003-Mar-01, 03:44 PM
So the image of Betelgeuse is done by a computer-enhanced Doppler imaging and is not a direct optical photo? What size telescope mirror in theory would be required to get an optical photo of a disc, in order to refute the Creationists and small-universe advocates who say that stars are very small or even just pin-point light sources as they appear to us?

<font size=-1>[ This Message was edited by: Yul on 2003-03-01 10:46 ]</font>

Glutomoto
2003-Mar-01, 05:13 PM
Sorry Yul,

I may have un-intentionally mis-lead you. The doppler image I presented in my posting above, is of the K0 giant star HD 12545 (= XX Triangulum) and not Betelgeuse.

The image of Betelgeuse that Tim Thompson's post was about is this one shown below.

http://www.aavso.org/vstar/vsotm/images/hubblebetel.jpg

It was taken using the Hubble Space Telescopes, Faint Object Camera. Tim's post also had two links about the Betelgeuse image.

HubbleSite NewsCenter. (http://hubblesite.org/newscenter/archive/1996/04/)

and

AAVSO's Variable Star of the Month. (http://www.aavso.org/vstar/vsotm/1200.stm)



Sorry about the mix up.

Yul
2003-Mar-01, 10:44 PM
Is the Hubble capable of resolving the discs of the nearest stars Alpha & Proxima Centauri?

Espritch
2003-Mar-02, 03:54 AM
I noticed that the scale with the image in one of the links shows Betelgeuse as being larger than the orbit of Jupiter. I'd just like to say: "Wow!"

<font size=-1>[ This Message was edited by: Espritch on 2003-03-01 22:55 ]</font>