Astronomy 201,
Problem Set 4: Due Thursday, October 4th (turn in with the
in-class exam)
Work out the two problems below related to Chapter 6 on Telescopes.
Two important notes about telescopes not in the textbook:
Magnification = (focal length of objective) / (focal length of eyepiece)
Magnification is of small consequence when buying a small telescope since it can be varied with eyepieces; size of objective and quality of mount is what’s important!
The f-ratio of a telescope is expressed as f/(number) where “number” = (focal length of the objective) / (diameter of the objective). An f/15 telescope is called “slow” because it over magnifies images compared to its light gathering power, while a f/5 telescope is called.
4-1. The Meade “16inch” at the Rice Campus observatory is a f/10 Schmidt-Cassegrain telescope with a 16.00 inch diameter objective mirror.
(a) What is the objective diameter in millimeters?
(b) What is the telescope’s focal length in millimeters?
(c) What is the magnification using a 31mm focal length eyepiece?
(d) What is the visual-light (wavelength = 500nm) diffraction limit of the telescope?
4-2. On December 18th Mars and the Earth will have closet approach for Mars’ current synodic year: the distance separating them will be 0.589 AU = 88.42 million km.
(a) If the true diameter of Mars is 6794 km, what would its angular diameter (in arcseconds in the sky, or through our telescope) be? (oh no…skinny triangle again!)
(b) Given your result for the diffraction limit in (d) above, what would be the size of surface features theoretically resolvable with our campus 16inch telescope?
(In reality, atmospheric turbulence limits this to a practical ~2 arcseconds from campus.)
FIRST EXAM NOTES:
Date: Thursday, October 4th, in-class (1:00-2:15pm, HBH 254). Closed Book (can have an optional sheet of paper with equations, constants, abbreviations written but no words; sheet must be turned in with the exam). The exam covers all material discussed in class related to Chapters 1-6 and S1 in the textbook. It will consist of: 10 multiple-choice questions taken from the basic skills and definition quizzes, 10 multiple-choice questions taken from the conceptual quizzes, and 5 multiple-choice questions generated by the prof. Finally, there will be 5 short problems to work out (using a calculator). The multiple-choice questions will be worth 3 points each and the problems 5 points each.