#### ASTR 100 - Homework 1 - McGaugh - Spring 2001

8. This answer will vary for each student. Weight-3 sif figs. The uncertainty is a matter of ounces – wht is taken in versus what is put out during the day. Height – 3 sig figs. The uncertainty is fraction of an inch , a matter of posture, stretching, weight, etc. Bank Balance – 3 sig figs. Usually! Automatic withdrawals can increase the uncertainty. Planet population – perhaps 3 sig figs .The rate of birth and death and the wildly inaccurate original data from some countries makes knowing it to better than 50 million very difficult. Modern scientists need to measure more significant figures to make progress because the larger dramatic effects have been studied – the effects left to study in order to make progress now are subtler.

3. a) A star just above the eastern horizon will appear to continue rising at an angle to the horizon (if you are standing anywhere other than equator or the poles ) . In the northern hemisphere, it will angle back "behind" the viewer as it gains altitude, so that as time passes , he will only be able to see it by craning over backwards if he’s facing north. Finally, it will ‘move’ back towards due west , and set.

b) A star just above the western horizon will set in a few minutes.

c) The North Star will not appear to move appreciably in course of the night.

d) A star just below the North Star will make a counterclockwise circle around the North Star, always at the same distance from the North Star, for as long as you see it .

5. a) Star rise 4 minutes earlier each night.

b) Assuming 30 – day months, Vega would set at 8 p.m. after 2 months .

c) Rising 1 hour earlier will take 15 days. Altair will rise at midnight in 15 days.

7. a) Difference in Sun’s height should measure 28° - 30° .

b) Should be same value found in part (a), perhaps with uncertainties estimated.

c) Anchorage , AK: 61° N; Tucson, AZ:32° N. Difference is actually 29° .

10. a) d = D a / 206,265 = 384,000km (1800") / 206,265" = 3,351 km.
Consulting Appendix B (p. 609), the Earth's diameter is 12,756 kilometers. Thus the Earth's radius is approximately 4 times larger than the moon's.

b) d = D a / 206,265 = 200 m (1800") / 206,265" = 1.74 m