Celestron 31041 Buku Petunjuk - Halaman 8

Jelajahi secara online atau unduh pdf Buku Petunjuk untuk Teleskop Celestron 31041. Celestron 31041 16 halaman. 3"/4.5" newtonian telesccope
Juga untuk Celestron 31041: Panduan Pengaturan Cepat (2 halaman), Panduan Pengguna (16 halaman)

Halaman Cetak
4
.
U
N
D
E
R
S
T
4
.
U
N
D
E
R
S
T
A.

The Celestial - Coordinate System.

The celestial-coordinate system is an imaginary projection of the Earth's geographical coordinate
system onto the celestial sphere which seems to turn overhead at night. This celestial grid is complete
with equator, latitudes, longitudes and poles.
The Earth is in constant motion as it rotates on its axis. Actually the celestial-coordinate system is
being displaced very slowly with respect to the stars. This is called precession and is caused by
gravitational influences from the Sun, Moon and other celestial bodies.
The celestial equator is a full 360º circle bisecting the celestial sphere into the northern celestial
hemisphere and the southern celestial hemisphere Like the Earth's equator, it is the prime parallel of
latitude and is designated 0º.
The celestial parallels of latitude are called "coordinates of declination (Dec.)", and like the Earth's
latitudes they are named for their angular distances from the equator. These distances are measured in
degrees, minutes and seconds of arc. There are 60 minutes of arc in each degree, and 60 seconds of arc
in each arc minute. Declinations north of the celestial equator are "+" and declinations south are "-".
The north pole is +90 and the south pole is -90 .
sphere, because this makes it easier to tell how long it will be before a particular star will cross a
particular north-south line in the sky. So, R.A. coordinates are marked off in units of time eastward
from an arbitrary point on the celestial equator in the constellation Pisces. The prime R.A. coordinate
which passes through this point is designated "O hours O minutes O seconds". We call this reference
point the vernal equinox where it crosses the celestial equator. All other coordinates are names for the
A
N
D
I
N
G
T
H
E
A
N
D
I
N
G
T
H
E
S
K
Y
S
K
Y
The celestial meridians of longitude are
called "coordinates of right ascension
(R.A.)", and like the Earth's longitude
meridians they extend from pole to pole.
There are 24 major R.A. coordinates, evenly
spaced around the 360º equator, one every
15º.
Like the Earth's longitudes, R.A.
coordinates are a measure of time as well as
angular distance. We speak of the Earth's
major longitude meridians as being separated
by one hour of time because the Earth rotates
once every 24 hours (one hour = 15°). The
same principle applies to celestial longitudes
since the celestial sphere appears to rotate
once every 24 hours. Right ascension hours
are also divided into minutes of arc and
seconds of arc, with each hour having 60
minutes of arc and each arc minute being
divided into 60 arc seconds.
Astronomers prefer the time designation for
R.A.
coordinates
coordinates denote locations on the celestial
8
even
though
the