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3. Alternately, attach the entire ETX Astro Telescope (including fork
mount), to a heavy-duty photo tripod. Attachment to a photo tripod
is effected by means of the threaded hole (3, Fig. 3) in the center
of the bottom surface of the telescope's drive base. This central
hole is threaded with the phototripod-standard 1/4-20 thread. We
emphasize, however, that only a strong, heavy-duty photo tripod,
designed to accept the weight of the 9 lb. (4.1 kg) ETX Astro
Telescope should be used in this application. Check with the
tripod manufacturer to confirm that the intended tripod is designed
to carry such a weight safely and securely, before mounting the
telescope in this way.
4. The optical tube assembly of the ETX Astro Telescope may also
be removed from its fork mounting, allowing the tube assembly to
be placed directly on to a standard photo tripod. To remove the
tube assembly from its fork mount, use one of the hex-wrenches
packed with the telescope to unthread the two attachment screws
(19, Fig. 1) located on each side of the optical tube's rear cell.
Then carefully slide the tube assembly out of the fork arms in the
direction of the telescope's eyepiece-end. The ETX's rear-cell includes a tripod adapter plate (8, Fig. 1) for
attaching the tube assembly directly to the 1/4-20 thread of any standard photo tripod.
Never use the ETX telescope to look at the Sun! Observing the Sun, even for the shortest fraction of a
second, will cause Instant and Irreversible damage to the eye, as well as physical damage to the telescope
itself.
2. Astronomical Observing
Used as an astronomical instrument, the ETX Astro Telescope allows full use of its many optical and
electromechanical capabilities. It is in astronomical applications where the ETX's extremely high level of optical
performance is readily visible. The range of observable astronomical objects is, with minor qualification, limited only
by the observer's motivation. Understanding how and where to locate celestial objects, and how those objects
move across the sky is fundamental to enjoying the hobby of astronomy. This section provides a basic introduction
to the terminology associated with astronomy, and includes instructions for finding and following celestial objects.
a. Celestial Coordinates
Celestial objects are mapped according to a coordinate system on the Celestial Sphere (Fig. 6), an imaginary
sphere surrounding Earth on which all stars appear to be placed. This celestial object mapping system is
Fig. 6: Celestial Sphere.
Earth's Equator onto the celestial sphere.
Just as on the surface of the Earth, in mapping the celestial sphere, imaginary lines have been drawn to form a
analogous to the Earth-based coordinate system of latitude
and longitude.
The poles of the celestial coordinate system are defined as
those two points where the Earth's rotational axis, if extended
to infinity, north and south, intersect the celestial sphere. Thus,
the North Celestial Pole is that point in the sky where an
extension of the Earth's axis through the North Pole intersects
the celestial sphere. This point in the sky is located near the
North Star, Polaris.
In mapping the surface of the Earth, lines of longitude are
drawn between the North and South Poles. Similarly, lines of
latitude are drawn in an east-west direction, parallel to the
Earth's Equator. The Celestial Equator is a projection of the
Fig. 5: Mounting the ETX Astro
Telescope to the optional ETX Field
Tripod.
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