Planet Risings
Unlike the stars, planets do not move at constant speeds.
The distance varies between successive positions of either the Sun,
Moon, or any other of the five planets against the background of
fixed stars.
Unlike the stars, planets also differ from fixed stars in their
rising and setting locations north and south along the horizon. Two
points may be noted:
- Limited Range: Fixed stars rise and set all along the eastern
and western horizon, while planets rise and set in a narrower
range. For the most part, assuming our latitude in Shawnee,
planets rise between roughly 30 degrees north and south of due
east (which is to say, roughly 60 to 120 degrees of azimuth, where
east is 90 degrees azimuth). And planets set roughly between 240
and 300 degrees azimuth (= about 30 degrees north and south of due
west). In other words, planets don't appear among the most
northerly or southerly stars.
- The rising at setting ranges for planets can be specified
as azimuth coordinates,
in which case most planets rise roughly within 60 degrees to
120 degrees azimuth, and set roughly within 240 degrees to 300
degrees azimuth.
- The Sun and Moon range most widely and reach extreme values
for the planets; about 23.5 degrees north or south for the Sun,
up to 28.5 degrees for the Moon.
- Alternatively, one can specify rising and setting positions
with respect to the ecliptic,
which does not coincide with due east or due west. The distinction
between the ecliptic and the
celestial equator was not
obvious, and involves numerous assumptions--such as circular
motion, or a sphere of fixed stars (rather than different bands of
relatively moving stars, etc.). The visible planets are mostly
confined to within 8 degrees of the ecliptic:
|
Planet
|
Range north or south of Ecliptic
|
|
Sun
|
0 degrees
|
|
Moon
|
5 degrees
|
|
Mercury
|
7 degrees
|
|
Venus
|
8.5 degrees
|
|
Mars
|
3 degrees
|
|
Jupiter
|
1.5 degrees
|
|
Saturn
|
3 degrees
|