Tracking Celestial Objects - SKY-WATCHER S11670 User Manual

Polaris, the "Pole Star" is less than one degree from the North
Celestial Pole (NCP). Because it is not exactly at the NCP, Polaris
appears to trace a small circle around it as the Earth rotates. Polaris
is offset from the NCP, toward Cassiopeia and away from the end of
the handle of the Big Dipper (Fig.i1).
Aligning your telescope to Polaris
Unlock the DEC lock knob and rotate the telescope tube until the
pointer on the setting circle reads 90°. Retighten the DEC lock knob.
Move the tripod so that the "N" at the base of the equatorial mount
faces north and the R.A. axis points roughly at Polaris. Use the two
azimuth adjustment knobs above the "N" to make fine adjustments in
azimuth if needed (Fig.i2). For more accurate alignment, look
through the finderscope and centre the Polaris on the crosshairs.
Along the R.A. axis shaft, the farther away from the back of the shaft
that you are the more accurate you will be (Fig.i3). Even though the
true celestial pole may be up to twice the moon's diameter away
(Polaris circles the pole once a day) you won't find this a problem
unless you are doing long exposure photography.
After a while you will notice your target drifting slowly North or South
depending on the direction of the pole relative to Polaris. To keep the
target in the center of the view, turn only the R.A. slow-motion cable.
After your telescope is polar aligned, no further adjustments in the
azimuth and latitude of the mount should be made in the observing
session, nor should you move the tripod. Only movements in R.A.
and DEC axis should be made in order to keep an object in the field.
Southern Hemisphere
In the Southern Hemisphere you must align the mount to the SCP by
locating its position with star patterns, without the convenience of a
nearby bright star. The closest star is the faint 5.5-mag. Sigma
Octanis which is about one degree away. Two sets of pointers which
help to locate the SCP are alpha and beta Crucis (in the Southern
Cross) and a pointer running at a right angle to a line connecting
alpha and beta Centauri (Fig.i4).
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 to follow or track objects as they
move through the field. The DEC. slow-motion control is not
needed for tracking. A R.A. motor drive can be added to
automatically track celestial objects by counteracting the
rotation of the Earth. The rotation speed of the R.A. drive
matches the Earth's rotation rate 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
doing astrophotography.
Fig.i1
+
NCP
Polaris
Cassiopeia
Fig.i2
Fig.i3
alpha
Fig.i4
Centauri
SCP +
Big Dipper
Little Dipper
Polaris
beta
Centauri
beta
Crucis
alpha
Crucis
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