and longitude on the celestial sphere. These
lines are known as Right Ascension and
Declination.
The celestial map also contains two poles
and an equator just like a map of the Earth.
The celestial poles are defined as those two
points where the Earth’s North and South
poles, if extended to infinity, would cross the
celestial sphere. Thus, the North Celestial
Pole is that point in the sky where the North
Pole crosses the celestial sphere. The North
Star, Polaris, is located very near the North
Celestial Pole.
So, just as an object’s position on the
Earth’s surface can be located by its latitude
and longitude, celestial objects may also
be located using Right Ascension and
Declination. For example: You can locate
Los Angeles, California, by its latitude
(+34°) and longitude (118°). Similarly, you
can locate the Ring Nebula (also known as
“M57”) by its Right Ascension (18hr) and its
Declination (+33°).
• RIGHT ASCENSION (R.A.): This Celestial
version of longitude is measured in units of
hours (hr), minutes (min), and seconds (sec)
on a 24 hour “clock” (similar to how Earth’s
time zones are determined by longitude lines).
The “zero” line was chosen to pass through
the constellation Pegasus, a sort of cosmic
Greenwich meridian. R.A. coordinates range
from 0hr 0min 0sec to 23hr 59min 59sec.
There are 24 primary lines of R.A., located
at 15-degree intervals along the celestial
equator. Objects located further and further
East of the zero R.A. grid line (0hr 0min 0sec)
carry higher R.A. coordinates.
• Declination (Dec.): This celestial version
of latitude is measured in degrees, arc-
minutes, and arc-seconds (e.g., 15° 27’ 33”).
Dec. locations North of the celestial equator
are indicated with a plus (+) sign (e.g., the
Dec. of the North celestial pole is +90°). Any
point on the celestial equator (such as the
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Earth. This mapping system is similar to
the system of latitude and longitude on
Earth surface maps.
In mapping the surface of the Earth,
lines of longitude are drawn between the
North and South Poles and lines of latitude
are drawn in an East-West direction, parallel
to the Earth’s equator. Similarly, imaginary
lines have been drawn to form a latitude
Fig. 7
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Rotation
of the
Earth
0 Dec.
South
Celestial
Pole
Right
Ascension
Star
Celestial
Equator
-90 Dec.
+90 Déc.
D
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c
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a
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North
Celestial
Pole
(Vicinity of
Polaris)
Looking at or near the Sun will cause irreversable damage to your eye. Do not point this telescope at or near the Sun. Do not look through the telescope as it is moving.
8
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