Starship Asterisk*

Solon wrote:Assuming it was scientifically possible to combine the capabilities of some of our most advanced instruments, say SOHO and Hubble, how large would the lens or mirror of a telescope need to be so that we could see Proxima Centauri, or preferably the nearest Sun-like star Alpha Centauri A, at the same level of detail, and at the same wavelengths, as SOHO shows us? I think it would be a neat "first" to see another star at such resolution, but could it ever be done?

Chris Peterson wrote:
At a mere 120 mm, the EIT instrument aboard SOHO has a very small aperture. To equal its resolution for a star 4 ly away would require a mirror sized up by a factor of about 250,000- the ratio of the distance to the Alpha Centaurus system and the distance from SOHO to the Sun. So you'd want a telescope with an aperture of around 30 km.

http://www.mrao.cam.ac.uk/telescopes/coast/coast.intro.html wrote:

[b][color=#0000FF]Cambridge Optical Aperture Synthesis Telescope[/color][/b]

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<<The quest for high angular resolution at optical wavelengths has prompted the development of a variety of techniques to overcome atmospheric seeing at astronomical sites. These include speckle interferometry, triple correlation, aperture masking, adaptive optics, and, with the advent of the Hubble Space Telescope, satellite observations.

Unfortunately these methods, when used on existing single telescopes, are in principle limited to resolutions no better than about 10 milliarcseconds. While this represents an improvement in resolution by a factor of around 40 over that achieved under typical observing conditions, it is still inadequate for many astronomical problems.

It is clear that long-baseline interferometry is the only realistic method for achieving higher resolutions.

The Cambridge Optical Aperture Synthesis Telescope (COAST) was planned as a coherent array of four telescopes operating in the red and near infra-red, using Michelson interferometry on baselines of up to 100m to give images with a resolution down to 1 milliarcsecond. It was the first instrument of its kind to exploit the techniques of aperture synthesis and closure phase at optical or infra-red wavelengths, producing the first images from an optical aperture synthesis telescope on 95/09/13 and 95/09/28.

The total cost of the telescope was around £850,000.

The astronomical objectives of COAST are to provide very high resolution images of a wide variety of stellar systems down to a red magnitude of 10, including: stellar surfaces, the envelopes of pre-main sequence stars, pulsating variables, circumstellar shells, compact planetary nebulae and close binary and multiple systems.>>

At a mere 120 mm, the EIT instrument aboard SOHO has a very small aperture. To equal its resolution for a star 4 ly away would require a mirror sized up by a factor of about 250,000- the ratio of the distance to the Alpha Centaurus system and the distance from SOHO to the Sun. So you'd want a telescope with an aperture of around 30 km. To give the same linear resolution Hubble is capable of (although Hubble is never pointed at the Sun) would require a mirror diameter of 600 km.

Solon wrote:Thanks for that info. A 600 km diameter mirror, sheesh, I won't hold my breath waiting for that one!
Anyway, I'm not going to pretend I understand how they do this, Optical Vortex Coronagraph Can Directly Image Extrasolar Planets , though I have done some reading on the phase singularity as applied to antennas, but if planets can be directly observed around a star 129 light years distant, isn't there some way to use this technology to see the star itself?
http://suite101.com/article/optical-vor ... ts-a226210
Thanks again!