- Circumpolar stars are always above the horizon (i.e., they never
set). There are more circumpolar stars closer to the poles.
At the north pole, the whole sky is circumpolar. Thus, the north
pole has many more circumpolar stars than anywhere in the United
states, even including Alaska.
- The sky appears and moves differently at different
Latitude determines the positions of the Celestial Poles and Celestial
Equator along the meridian. Thus, the motion of the sky relative
to the horizon and cardinal directions is determined by latitude.
Also, the amount of the sky that is circumpolar depends on latitude.
The sky does not vary with longitude, except for the exact time
of rises, sets and transits.
- The zodiac is the set of 12 constellations that line up with the
ecliptic and are traditionally used by astrology. When the sun is
aligned with a zodiac constellation, that constellation and neighboring
ones are above the horizon during the daytime hours and are not
visible. Thus, the zodiac constellations on the opposite side
from the Sun will be easy to see at night.
- If the Earth had no tilt to its spin axis, there would be no
seasons. Without a tilt, the path of the Sun on the sky would not
change with time of year.
- At the Summer Solstice, the Sun has the highest declination of
the year. In other words, the Sun would appear farthest to the
north with a declination of +23.5 degrees.
At the Winter Solstice, the Sun has the lowestt declination of the
year. In other words, the Sun would appear farthest to the south
a declination of -23.5 degrees.
At both Equinoxes, the Sun lines up with the Celestial Equator.
In other words, the Sun would appear with
a declination of 0 degrees.
- Precession is the slow wobble of the spin axis of the Earth witha
period of about 26,000 years. The wobble of the tilt of Earth's
spin axis is relative to the plane of the ecliptic.
- This planet should also have seasons because of its tilt.
The seaons would be more extreme than Earth. This new planet
would have greater seasonal differences in declination for its
"Sun". In other words, the seasonal differences in the
aliitudes of the Sun and the hours of sunlight are greatert on this
- The Celestial Equator would be aligned with your horizon at the
North Pole. The North Celestial Pole would be at your zenith and
the sky would rotate around your zenith with stars moving parallel to
the horizon. Hence, stars never rise or set/
At the Equator, the Celestial Equator would run from due East at the
horizon, through the zenith, to due West at the horizon. The
North Celestial Pole would lie at the horizon due North. Stars
would rise in the eastern half of the sky and set directly west.
Also, every object would set about 12 hours after rising.
At 40 degrees north, the Celestial Equator would run from due East to
an altitude of 50 degrees along the south of the meridian down to
due West. The North Celestial Pole would be at an altitude of 40
degrees along the north of the meridian. The sky would rise in
the east and slant toward the south until crossing the meridian.
After crossing the meridian, starts would set while slanting to the
north. Stars with declinations greater than +50 degrees would
never set, and starts with declinations less than -50 degrees would not
- These paths depend on latitude which in this case of 40 degrees
north. On the equnoxes, the Sun rises due east and sets due
west. The Sun spends 12 hours above the horisin and crosses the
meridian with an alitutde of 50 degrees along the South.
On the summer solstice, the Sun rises north of east and sets north of
west. The Sun spends more than 12 hours above the horizon and
crosses the meridian with an alitude of 73.5 degrees.
On the winter solstice, the Sun rises south of east and sets south of
west. The Sun spends less
than 12 hours above the horizon and crosses the meridian with an
alitude of 26.5 degrees.
- If the Earth rotated in the opposite direction once every 24
hours, the starts would rotate WEST to EAST once every 24 hours.
Because the Sun would still move about 1 degree EAST on average every
day, the sun would cross the meridian 4 minutes EARLIER every
day. Thus, the solar day would be SHORTER: 23 hours 56 min.
- Declination is measured positive to the north and negative to the
south and is the minimum angular distance between a celestial body and
the Celestial Equator. Right Ascension is the eastward angle from
the vernal equinox to the intersection of an object's hour circle with
the Celestial Equator typically measured in unit of hours equal to 15
degrees. The coordinates are similar to latitude and longitude on
Earth because they both measure north-south and east-west
positions. Also, declination has a set of positive and negative
values just like latitude has north and south. Howver, right
ascension differs from longitude because it is measured eastward only,
but longitude has sets of east and west values. Also, the untis
of right ascension are typically hours equal to 15 degrees while
longitude is measured in degrees,
- A solar day is determined by the length of time between meridian
crossings of the Sun, while the sidereal day is determined by the
motion of the stars. The mean time between meridian crossings of
the Sun is 24 hours, and the sidereal day is 23 hours 56
minutes. The difference is a result of the motion of the Sun
against the background stars of about 1 degreee per day.