Your First Astronomical Observing Session; The Moon; Celestial Observing Tips; Magnification - Celestron ASTROMASTER 70EQ Mode D'emploi

YOUR FIRST ASTRONOMICAL OBSERVING SESSION

THE MOON

Now you are ready to take your telescope out at night and do some real observing!
Let's start with the Moon The Moon takes about one month to go through a complete phase cycle, from new Moon to full
Moon and back again Try observing it at different points during this cycle
While you can observe the Moon any time it is visible in the sky, the best time to view it is from two days after a new Moon up to
a few days before a full Moon During this period, you will be able to see the most detail in craters and lunar mountain ranges
Consult a calendar to find out when the next new Moon will be
1 . With a clear view of the Moon, set up your telescope with the 20 mm eyepiece
2 . Turn on the finderscope and look through it to find the red dot
3 . Move the telescope until you can see the Moon through the finderscope's window and the red dot is centered on the Moon
4 . Look through the 20 mm eyepiece Gently turn the focus knobs to adjust the sharpness of the image
CONGRATULATIONS! YOU HAVE NOW OBSERVED YOUR FIRST CELESTIAL OBJECT!
You can view many other celestial objects, such as planets, star clusters and nebulae using this same basic technique

CELESTIAL OBSERVING TIPS

This section covers visual observing hints for both solar system and deep-sky objects as well as general observing
conditions which will affect your ability to observe

MAGNIFICATION

You can change the magnification of your telescope by simply changing eyepieces Both telescopes and eyepieces
have focal lengths that are measured in millimeters To calculate the magnification of a given telescope and eyepiece
combination, take the focal length of the telescope and divide it by the focal length of the eyepiece The resulting number
is the magnification factor
For example, the AstroMaster 90EQ has a focal length of 1000 mm Using the 20 mm eyepiece:
_________________________
Magnification =

FIELD OF VIEW

Determining the field of view is important if you want to get an idea of the angular size of the object you are observing To
calculate the actual field of view, divide the apparent field of the eyepiece (supplied by the eyepiece manufacturer) by the
magnification it gives you in the scope you are using
Using the example in the previous section, we can determine the field of view using the same telescope and 20 mm
eyepiece The 20 mm eyepiece has an apparent field of view of 40°
Actual Field Of View =
The 20 mm eyepiece has an apparent field of view of 40° Divide the 40° by the magnification, which is 50 power This
yields an actual field of view of 0 9 degrees or 54 minutes of arc
16 I ENGLISH
Focal length of Telescope
Focal length of Eyepiece
Apparent Field of View of Eyepiece
________________________________
Magnification
1000 mm
____________ = 50x
=
20 mm
40°
______ = 0 3 degrees of arc
=
50