ASTR108: Descriptive Astronomy
Recitation 1: Locating Objects in the Local Sky
1) On the “all-sky” chart below, label the altitude (in degrees) represented by each circle; label
the azimuth of the four cardinal directions (N, E, S and W); label the zenith; and label the
horizon.
2) The altitude and azimuth of several stars are listed in Tables 1 and 2. Chart each of these
objects on the all-sky plot below. Connect the objects of each table with a light line. Do you
recognize these groups of objects
Name
Alkaid
Mizar
Alioth
Megrez
Phecda
Merak
Dubhe
Table 1
Azimuth
41.0
39.0
40.5
42.0
47.5
47.0
39.5
Altitude
20.0
27.0
31.0
37.0
37.5
45.5
46.0
Name
Betelgeuse
Bellatrix
Alnitak
Alnilan
Mintaka
Saiph
Rigel
Table 2
Azimuth
194.0
205.5
196.5
198.5
200.0
192.5
203.0
Altitude
54.0
51.0
44.0
45.0
45.5
37.0
36.5
3) Label the all-sky chart below in the same way you did in part 1.
4) The approximate local position of Polaris (North Celestial Pole) is indicated by a “star”.
Trace the approximate position that other stars would travel during a 24 hour period. Briefly
explain this motion.
Due to the rotation of the Earth about an axis that coincides with the North Celestial Pole
(approximately where Polaris is located) the stars appear to move in circles about Polaris.
The stars that move in this circular pattern and never set are referred to as circumpolar stars.
[Additional Note: stars within your latitude of the pole will not set and thus be circumpolar.
For example, if you are at 60° latitude, all stars within 60° of the North Celestial Pole will
remain above the horizon as it circles Polaris. Thus any star with a latitude of greater than
30° will be circumpolar.
5) What is the approximate latitude of the observatory at the center or this chart. Explain.
As an observer moves equatorward to lower latitudes, Polaris appears lower in the sky.
(When the observer is at 90° latitude Polaris is approximately overhead. When the observer
is at 0° latitude, Polaris is near the horizon.) The relationship is such that the altitude of
Polaris in the local sky is equal to the latitude of the observer. For example, a person located
at 23° latitude will observe Polaris relatively low in the sky at an altitude of 23°.
6) If the observatory were located at the equator, where would Polaris be located (what would its
altitude be)?
The observer is at 0° latitude (the equator). Thus Polaris would be located at 0° altitude, that
is, on the horizon.
N
W
E
S