Celestron C4.5 User Manual

AS TRON OM Y BAS ICS
Up to this point, this manual covered the assembly and basic operation of
your C4.5 telescope. However, to use your telescope effectively, you need to
know a little about the night sky. This section deals with observational
astronomy in general and includes information on the night sky and polar
alignment.
The Celestial Coordinate To help find objects in the sky, astronomers use a celestial coordinate system
System that is similar to our geographical coordinate system here on Earth. The
celestial coordinate system has poles, lines of longitude and latitude, and an
equator. For the most part, these remain fixed against the background stars.
The celestial equator runs 360 degrees around the Earth and separates the
northern celestial hemisphere from the southern. Like the Earth’s equator, it
bears a reading of zero degrees. On Earth this would be latitude. However,
in the sky this is referred to as declination, or DEC for short. Lines of decli-
nation are named for their angular distance above and below the celestial
equator. The lines are broken down into degrees, minutes of arc, and
seconds of arc. Declination readings south of the equator carry a minus sign
(-) in front of the coordinate and those north of the celestial equator are either
blank (i.e., no designation) or preceded by a plus sign (+).
The celestial equivalent of longitude is called Right Ascension, or R.A. for
short. Like the Earth’s lines of longitude, they run from pole to pole and are
evenly spaced 15 degrees apart. Although the longitude lines are separated
by an angular distance, they are also a measure of time. Each line of longi-
tude is one hour apart from the next. Since the Earth rotates once every 24
hours, there are 24 lines total. As a result, the R.A. coordinates are marked
off in units of time. It begins with an arbitrary point in the constellation of
Pisces designated as 0 hours, 0 minutes, 0 seconds. All other points are
designated by how far (i.e., how long) they lag behind this coordinate after it
passes overhead moving toward the west.
Your Celestron C4.5 telescope comes equipped with setting circles that
translate the celestial coordinates into a precise location for the telescope to
point. The setting circles will not work properly until you have polar aligned
the telescope and aligned the R.A. setting circle.
Declination
Right
Ascension
Figure 5-1
The celestial sphere seen from the outside showing R.A. and DEC.
Astronomy Basics * 25

Celestron C4.5 Specifications

General

Brand	Celestron
Model	C4.5
Category	Telescope
Language	English