David's Astronomy - Notes 2009-12-04 (S00402)

Recent sessions have been showing increased star drift which have required that exposures are limited to under 90sec. An attempt to improve polar alignment was begun during the previous session (S401) but was interrupted by cloud, leaving the alignment worse than before. This was corrected and improved by a polar alignment adjustment at the beginning of session S402. The steps undertaken are detailed below.

Slewed to South Sky Point.
- Star Drift measurement over 7.2 minute period
    - Drift of 0.84 arc sec/min northwards
    - Polar Axis of the telescope mount is pointing 3.22 arc mins too far west (requiring that wedge is rotated slightly clockwise)
- Recorded Star Position. Jogged scope 3.22 arc min East
- Rotated scope/wedge clockwise to 're-centre' Star

- Star Drift measurement over 7.1 minute period
    - Drift of 0.27 arc sec/min southwards
    - Polar Axis of the telescope mount is pointing 1.04 arc mins too far east (requiring that wedge is rotated slightly anticlockwise)
- Recorded Star Position. Jogged scope 1.04 arc min West
- Rotated scope/wedge anticlockwise to 're-centre' Star

Slewed to West Sky Point
- Star Drift measurement over 7.2 minute period
    - Drift of 4.47 arc secs/min northwards
    - Polar Axis of the telescope mount is pointing 17.1 arc mins too low (requiring that scope axis is raised )
- Slewed to South Sky Point (for convenience and balanced scope position)
- Recorded Star Position. Jogged scope 17.1 arc min North
- Lowered wedge to raise scope axis and 're-centre' Star

Log file associated with Polar Alignment Check

Slew to South Sky Point
Slewing to Azimuth: 180.0deg, Altitude: 33.0deg

Measuring N-S Drift
Two pictures will now be taken separated by approximately 12 minutes
Do not move the scope during the operation.

  Taking 10s image (C)...      Ok        [00402018] 16:50:38UT Full 2x2 10s C
  Brightest Object...          X/Y =      532/367.6
  Linking image (GSC)...       Ok        Stars 45, Scale 1.610, Angle 179.5°

  Taking 10s image (C)...      Ok        [00402019] 16:57:50UT Full 2x2 10s C
  Brightest Object...          X/Y =      527/371.3
  Linking image (GSC)...       Ok        Stars 58, Scale 1.610, Angle 179.5°

  Time Interval :              7.20 mins
  Baseline Az :                179.7 degrees
  Declination Drift :          0.84 arc secs/min NORTHWARDS
  Polar misalignment :         3.22 arc mins (approx)

Operation...                   Completed

Measuring N-S Drift
Two pictures will now be taken separated by approximately 7 minutes
Do not move the scope during the operation.

  Taking 10s image (C)...      Ok        [00402023] 17:06:50UT Full 2x2 10s C
  Brightest Object...          X/Y =      513/348.3
  Linking image (GSC)...       Ok        Stars 68, Scale 1.610, Angle 179.5°

  Taking 10s image (C)...      Ok        [00402024] 17:13:57UT Full 2x2 10s C
  Brightest Object...          X/Y =      511/346.5
  Linking image (GSC)...       Ok        Stars 69, Scale 1.610, Angle 179.5°

  Time Interval :              7.12 mins
  Baseline Az :                184.4 degrees
  Declination Drift :          0.27 arc secs/min SOUTHWARDS
  Polar misalignment :         1.04 arc mins (approx)

- South sky point (Northern Hemisphere)
star drifts north --> scope's polar axis pointing too far west and needs turning clockwise
star drifts south --> scope's polar axis pointing too far east and needs turning anti-clockwise

Slew to West Sky Point
Slewing to Azimuth: 270.0deg, Altitude: 20.0deg

Measuring N-S Drift
Two pictures will now be taken separated by approximately 12 minutes
Do not move the scope during the operation.

  Taking 10s image (C)...      Ok        [00402026] 17:25:26UT Full 2x2 10s C
  Brightest Object...          X/Y =      232/30.6
  Linking image (GSC)...       Ok        Stars 36, Scale 1.612, Angle 179.4°

  Taking 10s image (C)...      Ok        [00402027] 17:32:36UT Full 2x2 10s C
  Brightest Object...          X/Y =      218/50.6
  Linking image (GSC)...       Ok        Stars 34, Scale 1.613, Angle 179.4°

  Time Interval :              7.17 mins
  Baseline Az :                271.3 degrees
  Declination Drift :          4.47 arc secs/min NORTHWARDS
  Polar misalignment :         17.09 arc mins (approx)

Operation...                   Completed

- West sky point (Northern Hemisphere)
star drifts north --> scope's polar axis pointing too low and needs raising
star drifts south --> scope's polar axis pointing too high and needs lowering

This Web Page:	Notes - Session 402 (2009-12-04)
Last Updated :	2015-05-16

David's Astronomy Pages
Notes - Session 402 (2009-12-04)

Polar Alignment Adjustment

	2009-12-04
	Polar Alignment Adjustment

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David's Astronomy Pages Notes - Session 402 (2009-12-04)

Polar Alignment Adjustment

David's Astronomy Pages
Notes - Session 402 (2009-12-04)