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divide the focal length of the telescope by the focal length of
the eyepiece:
Telescope focal length
Eyepiece focal length
For example, the SpaceProbe 130mm EQ, which has a focal
length of 900mm, used in combination with a 25mm eyepiece,
yields a power of
900mm
25mm
Every telescope has a useful limit of power of about 45x-60x
per inch of aperture. Claims of higher power by some telescope
manufacturers are a misleading advertising gimmick and
should be dismissed. Keep in mind that at higher powers, an
image will always be dimmer and less sharp (this is a funda-
mental law of optics). The steadiness of the air (the "seeing")
will also limit how much magnification an image can tolerate.
Eyepiece Selection
By using eyepieces of varying focal lengths, it is possible to
attain a great many magnifications with the SpaceProbe
130mm EQ. The telescope comes with two high-quality
Explorer II eyepieces: a 25mm, which gives a magnification
of 36x, and a 10mm, which gives a magnification of 90x.
Other eyepieces can be used to achieve higher or lower pow-
ers. It is quite common for an observer to own five or more
eyepieces to access a wide range of magnifications. This
allows the observer to choose the best eyepiece to use
depending on the object being viewed. At least to begin with,
the two supplied eyepieces will suffice nicely.
Whatever you choose to view, always start by inserting your
lowest-power (longest focal length) eyepiece to locate and
center the object. Low magnification yields a wide field of
view, which shows a larger area of sky in the eyepiece. This
makes acquiring and centering an object much easier. If you
try to find and center objects with high power (narrow field of
view), it's like trying to find a needle in a haystack!
Once you've centered the object in the eyepiece, you can
switch to higher magnification (shorter focal length eyepiece),
if you wish. This is especially recommended for small and
bright objects, like planets and double stars. The Moon also
takes higher magnifications well.
Deep-sky objects, however, typically look better at medium or
low magnifications. This is because many of them are quite
faint, yet have some extent (apparent width). Deep-sky
objects will often disappear at higher magnifications, since
greater magnification inherently yields dimmer images. This
is not the case for all deep-sky objects, however. Many galax-
ies are quite small, yet are somewhat bright, so higher power
may show more detail.
The best rule of thumb with eyepiece selection is to start with
a low power, wide field, and then work your way up in magni-
fication. If the object looks better, try an even higher
magnification. If the object looks worse, then back off the
magnification a little by using a lower-power eyepiece.
= Magnification
= 36x
Objects to Observe
Now that you are all set up and ready to go, one critical deci-
sion must be made: what to look at?
A. The Moon
With its rocky surface, the Moon is one of the easiest and most
interesting targets to view with your telescope. Lunar craters,
marias, and even mountain ranges can all be clearly seen
from a distance of 238,000 miles away! With its ever-chang-
ing phases, you'll get a new view of the Moon every night. The
best time to observe our one and only natural satellite is dur-
ing a partial phase, that is, when the Moon is NOT full. During
partial phases, shadows are cast on the surface, which reveal
more detail, especially right along the border between the dark
and light portions of the disk (called the "terminator"). A full
Moon is too bright and devoid of surface shadows to yield a
pleasing view. Make sure to observe the Moon when it is well
above the horizon to get the sharpest images.
Use an optional Moon filter to dim the Moon when it is very
bright. It simply threads onto the bottom of the eyepieces (you
must first remove the eyepiece from the focuser to attach a fil-
ter). You'll find that the Moon filter improves viewing comfort,
and also helps to bring out subtle features on the lunar surface.
B. The Sun
You can change your nighttime telescope into a daytime Sun
viewer by installing an optional full-aperture solar filter over
the front opening of the SpaceProbe 130mm EQ. The prima-
ry attraction is sunspots, which change shape, appearance,
and location daily. Sunspots are directly related to magnetic
activity in the Sun. Many observers like to make drawings of
sunspots to monitor how the Sun is changing from day to day.
Important Note: Do not look at the Sun with any optical instru-
ment without a professionally made solar filter, or permanent eye
damage could result.
C. The Planets
The planets don't stay put like the stars, so to find them you
should refer to Sky Calendar at our website (telescope.com),
or to charts published monthly in Astronomy, Sky & Telescope ,
or other astronomy magazines. Venus, Mars, Jupiter, and
Saturn are the brightest objects in the sky after the Sun and
the Moon. Your SpaceProbe 130mm EQ is capable of show-
ing you these planets in some detail. Other planets may be
visible but will likely appear star-like. Because planets are quite
small in apparent size, optional higher-power eyepieces are
recommended and often needed for detailed observations.
Not all the planets are generally visible at any one time.
JUPITER The largest planet, Jupiter, is a great subject for
observation. You can see the disk of the giant planet and
watch the ever-changing positions of its four largest moons -
Io, Callisto, Europa, and Ganymede. Higher-power eyepieces
should bring out the cloud bands on the planet's disk.
SATURN The ringed planet is a breathtaking sight when it is
well positioned. The tilt angle of the rings varies over a period
of many years; sometimes they are seen edge-on, while at
other times they are broadside and look like giant "ears" on
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