Homework 04
Please answer at least 4 of the following 5 questions correctly for full
credit:
Question 1
Please list the two main reasons why it is desirable to have a large aperture on
a telescope.
Answer
By enlarging the aperture one collects more light - which is important for
faint sources - and one reduces the size of the Airy disk for pointlike sources
- which means that diffraction is less limiting when it comes to the
resolution of the telescope.
Question 2
What are the main advantages of reflectors over refractors?
Answer
As we want large apertures, the weight of lenses is a serious consideration.
Another drawback of refracting optical elements is that refraction is wavelength
dependent, whereas reflection is not.
Question 3
For a plain 1m aperture telescope on the ground: What will be the
dominating effect that limits the resolution (resolving power) of the telescope
for blue light?
Answer
Atmospheric seeing.
Question 4
What is the longest baseline you could possibly get for interferometry without
leaving the Earth?
Answer
The diameter of the Earth.
Question 5 (the quantitative one...)
Looking at the atmospheric absorption portion of the figure on the inside of
your text book's front cover: If you want two IR telescopes, one to look
near a wavelength of 6 micrometers and one to look near a wavelength of 10
micrometers: Which one would you put into space? Please be aware that the
wavelength scale in the books figure is logarithmic; make sure you understand
where 6 micrometers is on that scale.
(Book: I am referring to the 6th edition; Desiree in JFB 201 has a copy for
you to look at if you do not have one yourself. You will not be able to take
it out of her office though. I also have a copy in my office.)
Answer
At 6 micrometers the atmosphere is not transparent, whereas there is a band of
transmission near 10 micrometers. So the 6 micrometer telescope will have to go
into space.
The deadline for submitting solutions to this homework has passed.
Last modified: Fri Feb 15 16:31:20 MST 2008