I did a rough calculation to see how powerful a telescope magnification must be, to see our own Earth from 20 Light Years away. The detail is written here :
http://scienceray.com/astronomy/how-powerful-a-telescope-must-be-to-see-earth-from-20-light-years-away/
Just to put things into perspective, I want to ask:
1. How powerful the magnification of Hubble Space Telescope?
2. How powerful the planned magnification of James Webb Space Telescope ?
3. When do you think we will have telescope as powerful as described in the article ?
Telescopes are not measured by their magnifying power, since that varies depending on the eyepiece or camera used. What is more important is their light gathering power, determined by the area of their objective (main lens or mirror), and their resolution, determined by its diameter. Spotting a planet close to a distant star is a complex matter, depending on the size of the planet, its distance from the star, and the brightness of the star, as well as the distance of the planet. Seeing a tiny speck of reflected light next to a brilliant star is a major optical challenge
January 22nd, 2010 at 8:50 pm
Telescopes are not measured by their magnifying power, since that varies depending on the eyepiece or camera used. What is more important is their light gathering power, determined by the area of their objective (main lens or mirror), and their resolution, determined by its diameter. Spotting a planet close to a distant star is a complex matter, depending on the size of the planet, its distance from the star, and the brightness of the star, as well as the distance of the planet. Seeing a tiny speck of reflected light next to a brilliant star is a major optical challenge
References :
January 22nd, 2010 at 9:01 pm
Geoff G is right on his answer. "Most instruments on Hubble contain more than one optical channel, each of which produces different magnification."
But I have seen an estimate for the Hubble to see details on Mars as if it was 4800X.
"Installed during Hubble servicing mission 1, in 1993, WFPC2 is the most commonly used camera on the HST. It responds to light from ultraviolet to near-infrared wavelengths and is equipped with 48 filters for color imaging and photography. Its sensor actually consists of four separate CCDs. Three of the CCDs are “wide-field cameras,” and one is a “planetary camera” with a much smaller field of view and higher resolution."
"Hubble can see detail down to less than 0.1 arcsecond across."
Doing a simple comparison, if my ten inch Celestron SCT can give 1 arcsec resolution on good nights and I can still see clearly at about 500X, then the Hubble MIGHT be able to give good images at about 5000X under the best conditions.
Telescopes cannot be built much larger in one location than they are now, given current knowledge of materials and engineering. The fact that they distort under their own weight here on Earth is the limit. But in space or on the moon, several good ideas could create an interferometer, or a synthetic aperture array of smaller scopes that have no weight problem. A telescope made from several linked mirrors on the Moon or in space across the solar system are planned for the future. They could do high resolution work that could see small objects light years away.
Now work is being done to image star surfaces (Betelguese) and dots of light from orbiting planets around other stars give strength that these future plans will give good performance and information.
References :
http://www.planetary.org/explore/topics/hubble/instruments.html
http://hubblesite.org/the_telescope/nuts_.and._bolts/res101.php