If a 150cm telescope can resolve two stars with a seperation of 0.85 arc-seconds, what is the minimum sep...?

Question

If a 150cm telescope can resolve two stars with a seperation of 0.85 arc-seconds, what is the minimum separation of two stars that can be clearly resolved with a 1.5 meter telescope? What is this minimum seperation called? You don't need a calculator to complete this problem. (This is a problem im working on for school ,any help would be really appreciated)

Answer 1

Look up Dawes Limit in wiki ...

NB. in the real world (something that has never bothered school teachers, as far as I can tel) it's a LOT more difficult to build an accurate 1.5m telescope than a 150mm one ..  so the 'real world answer is' :-

"it depends on the accuracy of the optics" (and how much you are prepared to pay)

Answer 2

The Dawes limit depends only on the size of the aperture of the telescope, and is linear.

I bet they said 150 mm telescope (about 6") and 1.5 meter telescope (1500 mm) as 150 cm is already the same as 1.5 meters.  So, i'll answer that question.  If it's ten times larger, the Dawes limit is ten times smaller.  So instead of 0.85 arc seconds, it would be 0.085 arc seconds.

The Dawes limit does not take into account atmospheric disturbance.  A 1.5 meter telescope will not perform this well.  To improve it's performance, put it up on a tall mountain. Add adaptive optics.  Or put the whole thing into space.