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Comment by tigershark | Hacker News Reader

Seriously are you asking me to "study" astronomy? I was doing astronomical research (planetoids, variable stars, supernovae) 20-something years ago. And M31 is not "almost" visible to the naked eye. It is perfectly visible unless you live under a light polluted sky. The objects that I captured I think were just below the 17th magnitude. As I said before extremely dim objects cannot be seen simply increasing the aperture because that is helpful only for point sources. Hubble Space Telescope captured some of the most dim objects in the universe. With a "very small" mirror compared to some much bigger on this planet.

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I'm aware HST has a relatively small diameter (2.4m), but how much of its resolving power (for lack of a better phrase) can be attributed to it being above the atmosphere? I've also heard that modern adaptive optics systems do a good job of mitigating atmospheric effects (turbulence?) for ground based telescopes -- I wonder if a ground-based "Hubble deep field" image could be generated?

Most of the HST resolving power is due to the fact of being outside of the atmosphere. Adaptive optics have been improving in the last 20 years if I recall correctly, but even with the advancement in lasers to generate improved artificial stars and in the segmented mirrors to have a better atmospheric correction in real time, they still can't do anything regarding the loss of trasmission, especially in wave lengths different from the visible light window. The fact that with a "small" diameter in nearly-ideal conditions you can have better results than much bigger apertures on the earth is still a testament that aperture alone can't do miracles, especially when there is a lot of noise. And don't forget that HST optics are flawed. Before the servicing mission that added the correction we were relaying on software adjustments. And even with that huge handicap the results were nothing short of amazing.

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