ASTR 3510
Astronomical Observations and Instrumentation I: Imaging
Fall 2009
Homework 1:
Due: 1 September 2009 (Tuesday in class)
Purpose:
Exercise simple concepts of light, energy, and optics.
1) Photon properties
a) What is the frequency of visual light having a wavelength of 5,500 Angstroms?
b) What is the energy of a photon in part a). Give your answer in ergs and eV.
c) Suppose you have a 1 milli-Watt laser at 5,500 Angstroms. How many photons per
second does it emit?
2) Telescope optics.
The 24” telescope at SBO is an f/8 Cassegrain system.
a) What is the effective focal length at the Cass focus in cm?
b) What is the expected image scale in arc-seconds per millimeter at the focus?
c) If you use a 2 cm x 2 cm square format detector at the focus, what is the field-of-view
of this device?
d) Suppose you use a 30 mm focal length eyepiece for visual observations at the Cass focus of the
24”, what is the magnification?
e) If the apparent field of view (FOV) of this eyepiece is 80 degrees, what is the true field of view
on the sky?
f) Under perfect conditions, what is the theoretical angular resolution limit of the 24” at 5,500
Angstroms?
3) Black-body radiation. How much energy is given off by a 1 square cm emitter, into 1
steradian, at a temperature of T = 6,000 K at a wavelength of 5,500 Angstroms in to a band-pass
of 1,000 Angstroms centered at 5,500 Angstroms? Don’t do the integral ….use the “rectangular”
approximation we discussed in class.