how are we able to see planets that are 100’s of lightyears away? By continually increasing the magnification of a telescope? How do we know anything about the planets atmosphere if it’s that far away? For example, the Corot-7b, we are told it rains rocks there.
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We aren’t current capable of imaging planets *light years* away. The farthest planet scale objects we’ve imaged directly are within the Outer Kuiper Belt about 50 Astronomical Units (AU) away. 1 light year equals 63,241 AU. So the farthest planets we’ve directly imaged are on the order of 1/1,000th of a L.Y.
1 AU, in turn is roughly the Earth-Sun distance or 8.3 light-minutes.
We can detect extra-solar planets indirectly through several methods. The simplest is when a planet passes directly in front of a star, which slightly dims it in brightness, which can be measured with highly sensitive photometers. This can’t produce a clear image of the planet directly.
Increasing the magnification of a telescope by itself isn’t useful, because at a certain point [optical fringing effects become larger and stronger than the size of the object you want to image.](https://en.wikipedia.org/wiki/Angular_resolution) Thus, completely obscuring a planet in a haze optical noise around it’s parent star. This is an unavoidable physical consequence of the wave nature of light. This problem is made worse in the situation of trying to discern a very luminous object (a star) with a quite faint one near to it.
The size of these fringing effects are related to both the size of the primary mirror and the wavelength of light.
Increasing the effective size of the telescope apeture is the only real way around this problem. Simply using a larger mirror is one option.
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