How far can modern telescopes see?
1 Answer
Billions of light years. For optical telescopes, the magnitude of the celestial object determines its visibility. Increasing telescope aperture aids in light gathering for improved resolution.
Explanation:
Celestial objects like stars and nebula are assigned a numeric value called its magnitude which reflects the brightness of an object. The smaller the magnitude the brighter the object. The human naked eye can see objects with a magnitude around 6 and lower.
For higher magnitudes a telescope or binoculars is needed. These actually serve as light gathering instruments. The larger the aperture of the primary (Front) lens the more light is gathered allowing for better resolution and identification of faint objects.
For example the Ring Nebula M57 is so faint that it cannot be seen with the naked eye or through a pair of Sky Binoculars (15x70mm). A 100 mm aperture telescope will reveal its position in the Constellation Lyra. This object is estimated by astronomers to be about 2300 light years away.
If our Sun however was placed at 22000 light years away its magnitude would be about 19 and you would need a telescope of at least 1000 mm aperture to observe.
The largest optical telescope on earth is a whopping 30 m consisting of an array of segmented mirrors.
Radio telescopes are the next giants working on the non visible spectrum. If placed strategically at different points on earth their combined effect can parallel that of a telescope as big as the size of our planet. These telescopes can reveal detail finer than
optical telescopes.
http://www.universetoday.com/110858/how-far-can-you-see-in-the-universe/
