Download Physics 127 Descriptive Astronomy Homework #2

Physics 127 Descriptive Astronomy
Homework #2 Key (Website)
Winter 2015
A-1. A star is in the southwestern part of the sky, one-third of the distance from the horizon to the
zenith. What is its azimuth? What is its altitude?
Since azimuth is measured eastward from a starting value of 0° in the north, a star in the southwest has an azimuth of
5/8 of a full circle or azimuth = 5/8  360° = 225°. Similarly, the altitude of the star is 1/3 of the angle from the horizon
to the zenith or altitude = 1/3  90° = 30°.
A-2. An observer notes that the stars neither rise nor set but move right to left, parallel to her
horizon. What is her location?
At the South Pole.
A-3. An observer views a star that crossed the celestial meridian 2 hours 20 minutes earlier. His
sidereal clock says 15 hours 28 minutes. What is the right ascension of the star?
α = LST – HA = 15h 28m – 2h 20m = 13h 8m.
A-4. As viewed from Provo (latitude = +40°), a star transits (crosses the celestial meridian) south of
the zenith at an altitude of 63°. What is the star's declination? What is the declination of a star
which passes through Provo's zenith?
Since the altitude of the celestial equator, where it intersects the celestial meridian is 90° − observer’s latitude = 50° in
Provo, a star which transits at an altitude of 63° must have a declination of 𝛿 = ℎ − 50° = 13°. The declination of any
star which passes through the zenith must be 𝛿 = 90° − 50° = 40°, i.e., its declination must equal Provo’s latitude.
A-5. An observer notes that the sun spends 12 hours per day above his horizon regardless of the
month of the year. What is his location?
On the equator.
A-6. The track of a star which rises directly in the east is shown with
respect to an observer's horizon. The observer's location is (a)
near but not at the north pole, (b) at an intermediate northern
latitude, (c) near but slightly north of the equator, (d) on the
equator, (e) near but slightly south of the equator, (f) at an
intermediate southern latitude, (g) near but not at the south pole.