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Inverted image, as viewed with
the eyepiece directly in telescope
Actual image as seen with the
unaided eye
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g
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Focusing
To focus your telescope, simply turn the focus knob located directly below the eyepiece holder. Turning the knob clockwise
allows you to focus on an object that is farther than the one you are currently observing. Turning the knob counterclockwise
from you allows you to focus on an object closer than the one you are currently observing.
• If you wear corrective lenses (specifically glasses), you may want to remove them when observing with an eyepiece
attached to the telescope. However, when using a camera you should always wear corrective lenses to ensure the
sharpest possible focus. If you have astigmatism, corrective lenses must be worn at all times.
The Celestial Coordinate System
To help find objects in the sky, astronomers use a
celestial coordinate 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 declination
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 (+).
Figure 8
The celestial sphere seen from the outside showing R.A. and DEC
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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 longitude 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.
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