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photo:telescope_alignment

telescope polar alignment and balancing

see also:

  • software to assist polar alignment with use of webcam:
  • software that calculates how much drift & field rotation will occur for a given error in polar alignment:
    • for a star at 0 deg declination and 0 hour angle (ie. at meridian):
      • for each 1 deg error in polar alignment upwards, you will get 0.034 arc-seconds drift (this increases rapidly with increasing hour angle but not much on declination) and 0.004 degrees of field rotation per minute.
      • for each 1 deg error in polar alignment West, you will get -15.7 arc-seconds drift (this is independent of star's declination) and 0 degrees of field rotation (this will increase if star is at declinations more than ~45deg north or south) per minute.

Why do we need to do this?

  • a nicely aligned telescope allows the equatorial mount to track the motion of the stars accurately which makes viewing easier and allows for much better quality astrophotos.
  • although one could use guiding software to correct for alignment errors in long photographs, alignment error will result in field rotation whereby the stars in the outer parts of the image will develop a curved track.

 

Initial approximate polar alignment:

  • ensure your finder scope is in alignment with your telescope by locating a bright star in the telescope and then align the finder scope.
  • aim the equatorial mount at the celestial pole relevant for your hemisphere  - in the Northern Hemisphere, aim for Polaris, in the South you have to guess based on the orientation of the Southern Cross (Crux) and Achenar +/- the Pointers (alpha & beta Centauri).
  • ensure the base of your equatorial mount is LEVEL
    • If the mount is not level, any adjustments in azimuth or altitude will cause an error in the alignment of the other component.
  • ensure the mount is set for YOUR latitude
  • then use one of the more precise alignment methods to fine tune it.

for Melbourne, Australia

  • latitude is ~38° S
  • there is ~12° east magnetic variation thus true South is 168° by compass

3 star alignment:

 

Drift alignment method:

  • preferably need an illuminated reticle eyepiece to assist in determining direction of drift and align the cross-hairs N-S and E-W;
  • essentially first step is to adjust the mount's azimuth until an equatorial star at the meridian stays bisected by an reticle line for 5 minutes
    • in Nth hemisphere, if star drifts south, you need to rotate azimuth of mount towards the west
  • then repeat and adjust the mount's altitude until an equatorial star 20deg above the East horizon stays bisected by a line for 5 minutes.
    • in Nth hemisphere, if star drifts south, you need to elevate the polar axis of the mount
  • mnemonic for the Nth hemisphere using meridian & East horizon stars: S-E-L ie. if star drifts South mount is too East &/or too Low
  • see an online video of how to do polar drift alignment: 

 

Clay's Kochab's clock method:

 

photo/telescope_alignment.txt · Last modified: 2013/05/18 10:47 by gary1