Polar Alignment - Dorr DANUBIA ATLAS 2000 Bedienungsanleitung

07.8 FOCUSING
Slowly turn the focus knobs under the focuser, one way or the other, until the image in the eyepiece is sharp
(Fig.h). The image usually has to be finely refocused over time, due to small variations caused by temperature
changes, flexures, etc. This often happens with short focal ratio telescopes, particularly when they haven't
reached outside temperature yet. Refocusing is almost always necessary when you change an eyepiece or
add or remove a Barlow lens.
07.9

POLAR ALIGNMENT

In order for your telescope to track objects in the sky you have to align your mount. This means tilting the
head over so that it points to the North (or South) celestial pole. For people in the Northern Hemisphere this is
rather easy as the bright star Polaris is very near the North Celestial Pole. For casual observing, rough polar
alignment is adequate. Make sure your equatorial mount is level and the red dot finder is aligned with the
telescope before beginning.
Setting the latitude
Look up your latitude on a map, road maps are good for this purpose. Now look at the side of your mount head,
there you will see a scale running from 0-90 degrees. At the base of the head, just above the legs, are two
screws opposite each other under the hinge. All you have to do is loosen one side and tighten the other until
your latitude is shown by the indicator pointer (Fig.i). 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 allignment, 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).
07.10 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 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.h
Fig.i
Fig.i1
Fig.i3
Fig.i4
omega Octanis
+NCP
21
Latitude scale
Big Dipper
Little Dipper
Polaris
Cassiopeia
Fig.i2
Polaris
alpha Centauri
beta Centauri
alpha Crucis
beta Crucis