Physics 112 Name________________________________

Astronomy

Dr. Kolan

EXAM I

March 1, 2004

I pledge my honor that during this examination I have neither given nor received assistance, and that I have seen no dishonest work.

Signed________________________________

I have intentionally not signed the pledge.__________________________

1) Define the following terms. (2 pts apiece)

a) right ascension The analogue of longitude on the celestial sphere.

b) epicycle A device used by Ptolemy to describe the motion (particularly retrograde motion) of the planets. The planet orbited on a small circle called the epicycle that was located on the larger deferent circle.

c) vernal equinox (place definition) One of the intersections of the celestial equator and the ecliptic.

d) precession The earth's axis makes a small circle over time--this implies that the North Celestial Pole changes over time. This changing of the NCP is called precession.

e) ecliptic There are two definitions of the ecliptic. The apparent path of the sun against the background stars OR the plane of the earth's orbit around the sun.

2) On October 27, 2004 there will be a total eclipse of the sun. What is the phase of the moon on that date? In which constellation will the moon be on that date? (5 pts)This question was deleted from the exam (because there is a lunar eclipse on October 27, not a solar eclipse).

3) Why don't we have an eclipse every two weeks? (5 pts) The moon's orbit is inclined by 5 degrees to the ecliptic. So for most full and new moons, the earth, moon, and sun are not in a line.

4) List Kepler's three laws. (5 pts)

1. A planet orbits the sun in an ellipse with the Sun at one focus.

2. A line from the Sun to the planet sweeps out equal AREAS in equal times.

3. P²=kR³, where P is the period of the planet, R is the average distance of the planet from the sun, and k is a constant that is the same for all planets.

5) Identify the phase of the moon if at sunset the moon is high in the southern sky. Assume that you are viewing from a northern latitude. (5 pts) First quarter.

6) Suppose that the moon orbited clockwise around the earth and that the earth orbited the sun counterclockwise (both motions as viewed form the north). Would the synodic month be longer than, equal to, or shorter than the sidereal month? Explain your answer with a diagram. (5 pts)

The sidereal month is the time that it takes the moon to revolve 360 degrees around the earth. The synodic month is the time that it takes the moon to go from new moon to new moon. As you can see from the diagram, in this case the synodic month is shorter than the sidereal month.

7) Of the stars Regulus, Alpheratz (in Pegasus), and delta Orion, which rises due (or nearly due) east? Support your answer. (5 pts)

All objects on the celestial equator rise due east and set due west. Delta Orion is the only star that is on the celestial equator.

8) If the Earth rotated clockwise on its axis instead of counterclockwise (as viewed from the north), (5 pts)

a) Our seasons would occur in reverse order.

b) We would not have seasons.

c) Daylight periods would be longer in winter and shorter in summer.

d) Winter in the Northern Hemisphere would occur in July.

e) None of the above.

E

9) If the earth did not rotate on its axis could we define the celestial poles and the celestial equator? The ecliptic? (5 pts)

The rotation of the earth is what defines the north and south poles and hence the equator. The projection of the earth's poles and equator onto the celestial sphere defines the celestial poles and celestial equator. So the answer is NO--if the earth were no rotating we could not define the celestial poles and celestial equator.

We could, however, define the ecliptic. The earth's revolution about the Sun changes the apparent position of the sun against the background stars.

10) Stars with a declination less than __-58^o______ can never be viewed from Tucson (latitude 32^o). Support your answer with a diagram. (10 pts)

11) Will you ever see Mars in the Big Dipper? Why or why not? (5 pts)

No, you will never see Mars in the Big Dipper. The planets all lie along the ecliptic and hence must be in one of the constellations of the zodiac. The Big Dipper is not a zodiac constellation.

12) As a star rises and moves across the sky, which of the following change (5 pts)

a) Its right ascension

b) Its declination

c) Its azimuth

d) Both a and b

e) None of the above.

C

13) Suppose that you live at a latitude of 40^o N. What is the altitude of the Sun above the southern horizon at noon at the time of the winter solstice? Explain your reasoning. Include a drawing as part of your explanation. (10 pts)

The Sun will be 26.5 degrees above the south horizon. See diagram.

14) Sirius is due south and is 8^o above the horizon. Greenwich sidereal time is 8:05 hrs. What is your latitude and longitude? (10 pts)

Your latitude is 65 degrees north. See the diagram.

To calculate your longitude first find the right ascension of Sirius. It is 6 hrs 45 min. When Sirius transits (as it is doing in this problem), the local sidereal time is 6 hrs 45 min. Since Greenwich is later than you are, you know that Greenwich is east of you--or you are west of Greenwich. You are west by 1 hr 20 minutes. At 15 degrees of longitude for each hour, this means that you are 20 degrees west of Greenwich.

15) Which planets are currently visible at 8 PM? List the planets and where they are located in the sky (north, south, east , or west). (5 pts)

If you look on your Sky-Gazer's Almanac, you can see that Jupiter rose at a little before 6 on March 1. So it will still be in the east at 8 PM. Saturn transits at 7:45 so it is in the south at 8. Venus sets at 9:30 so it will be in the west, and Mars sets close to 11:30 so it is in the southwest.

16) Who was associated with precise measurements of planetary positions? Who is associated with the first comprehensive heliocentric model? (5 pts)

Tycho Brahe was associated with the first precise measurements of planetary positions. Copernicus is associated with the first comprehensive heliocentric model.