Polar Alignment

Polar Alignment

Polar alignment is the process of aligning the mount so that it points at the NCP (the North Celestial Pole) or the SCP (South Celestial Pole). This means that the axis of the mount will then be aligned parallel to the earth's axis. It should be noted that Polaris, although being accepted as the North Star, is not quite at the the NCP. For polar alignment in the northern hemisphere, it is necessary to offset the mount a fraction of a degree from Polaris.

An accurate polar alignment is essential for long exposure imaging. It will also have some effect on alignment. Mounts with a polarscope usually have a reticule that is visible as you look through the polarscope. The reticle will typically have a circle that is the correct distance from the NCP. Positioning the mount by adjusting the physical adjusting bolts so that Polaris appears on the circle will align the mount. It is important to know where on the circle to position Polaris. For some mounts the reticle lighting is so bright it may be hard to see Polaris. Try with the power off as there is no reason to have the mount powered up for polar alignment (except for the light on the reticle) although you can't turn off the power if you're using the motors to align the hole in the shaft for the polarscope (unless you are prepared to reset home position etc.)

The position of Polaris on the circle is described by its Hour Angle.

  • The most recent version of the hand controller firmware will give you the hour angle of Polaris once the hand controller has been initialize with time/date location.
  • EQMOD provides you with the current Hour Angle (Polaris HA).

  • Also many planetarium programs will also give you this information. In addition,a freeware program know as PolarFinder.exe will also give you the required information. You may have to search the internet for this program. One page that might contain the link can be found http://arnholm.org/astro/polar_alignment/index.html . The page also has an interesting description of the process of polar alignment.
  • Remember that the view of Polaris is usually inverted through the polarscope. The PolarFinder.exe program shows you the view you should expect to see with most polarscopes.
  • Count the hours in the hour angle CCW starting at the bottom of the clock as 24h/0h, remember that it there are 24 hours in the full circle (not 12).
  • many reticles have a small circle on the larger circle used for positioning Polaris. Set this small circle according to the hour angle.
/home/welshdra/public_html/eqmod/data/pages/polar_alignment.txt · Last modified: 2010/05/26 18:22 (external edit)
Recent changes RSS feed Donate Powered by PHP Valid XHTML 1.0 Valid CSS Driven by DokuWiki