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Levenhuk Skyline PRO Telescopes
EN
Tracking celestial objects
When observing through a telescope, astronomical objects appear to move slowly through the
telescope’s field of view. When the mount is correctly polar aligned, you only need to turn the R.A.
slow-motion control to follow or track objects as they move through the field. A R.A. motor drive can
be added to automatically track celestial objects by counteracting the rotation of Earth. The rota
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tion speed of the R.A. drive matches the rotation rate of Earth for stars to appear stationary in the
telescope eyepiece. Different tracking speeds are also available in some models. A second drive can be
added to give Dec. control which is very useful for astrophotography.
The quickest way to find objects is to learn the constellations and use the finderscope, but if the
object is too faint you may want to use setting circles on an equatorial mount. Setting circles allow you
to locate celestial objects whose celestial coordinates have been determined from star charts. Your
telescope must be Polar aligned and the R.A. setting circle must be calibrated before using the setting
circles. The Dec. setting circle was calibrated at the factory and no additional calibration is required
for it.
The telescope’s R.A. setting circle is scaled in hours, from 1 to 24, with small lines in between
representing 10 minute increments. The upper set of numbers applies to observations in the Northern
Hemisphere, while the numbers below them apply to observations in the Southern Hemisphere.
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Setting (calibrating) the R.A. setting circle
In order to set your Right Ascension circle you must first find a star in your field of view with known
coordinates. A good one would be the 0.0 magnitude star Vega in the Constellation Lyra. From a star
chart we know the R.A. coordinate of Vega is 18h 36m.
Loosen
the R.A. and DEC. lock knobs on the mount and adjust the telescope so that Vega is centered in
the field of view of the eyepiece. Tighten the R.A. and DEC. lock knobs to lock the mount in place. Now
rotate the R.A. setting circle until it reads 18h36m. You are now ready to use the setting circles to find
objects in the sky.
Pointing in any direction other than due North requires a combination of R.A. and Dec. positions. This
can be visualized as a series of Dec. arcs, each resulting from the position of rotation around the R.A.
axis. In practice however, the telescope is usually pointed, with the aid of a finderscope, by loosening
both the R.A. and Dec. locks and swiveling the mount around both axes until the object is centered in
the eyepiece. The swiveling is best done by placing one hand on the telescope tube and the other on
the counterweight rod, so that the movement around both axes is smooth, and no extra lateral force is
applied to the axis-bearings. When the object is centered, make sure the R.A. and Dec. locks are both
retightened to hold the object in the field of view and allow tracking by adjusting R.A. only.
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Telescopes with long focal lengths often have a “blind spot” when pointing near the zenith, because
the eyepiece-end of the optical tube bumps into the mount’s legs. To avoid this, the tube can be very
carefully slipped up inside the ring clamps. This can be done safely because the tube is pointing almost
vertically, and therefore moving it does not cause a Dec. balance problem. It is very important to move
the tube back to the Dec. balanced position before observing other sky areas.
Something which can also be a problem is that the optical tube often rotates so that the eyepiece,
finderscope and the focusing knobs are in less convenient positions. The diagonal mirror can be rotated
to adjust the eyepiece. However, to adjust the positions of the finderscope and focusing knobs, loosen
the tube rings holding the telescope tube and gently rotate it. Do this when you are going to observe
an area for while, as it is inconvenient to repeat every time you briefly go to a new area.
Fina
lly, there are a few things to consider to ensure that you are comfortable during the viewing
session. First is setting the height of the mount above the ground by adjusting the tripod legs. You must
consider the height that you want your eyepiece to be, and if possible plan on sitting on a comfortable
chair or stool. Very long optical tubes need to be mounted higher or you will end up crouching or lying
on the ground when looking at objects near the zenith. However, a short optical tube can be mounted
lower so that there is less movement due to vibration sources, such as wind. This is something that
should be decided before going through the effort of polar aligning the mount.
