Drift Method Mount Alignment

These notes describe the polar alignment of an equatorial mount via the drift method.

Note: This is for southern hemisphere

A CCD camera is best, or use an illuminated reticle with high magnification (circa 400).

1) Point scope at star close to Celestial Equator and near E horizon (~20^o above horizon and <5^o dec from Celestial Equator)

2) Track with RA only (Dec tracking off)

3) Observe star drift. If it drifts north, then polar axis is too low. Adjust until drift is negligible.

4) Point scope at star close to Celestial Equator and near local meridian (~0.5hr RA from meridian and <5^o dec from Celestial Equator)

5) Again track with RA only

6) Observe drift. If star drifts south, the polar axis is west of south. Adjust until drift is negligible.

7) Cycle 1->6 a few times as adjustment is slightly interactive.

Easy Adjustment Rules

AltitudE is Easy, AziMuth is Mad

• For altitude, adjust so that drifted star is recentered.
• For azimuth, adjust in direction of drift

This takes care of optics inversions, etc.

The mount angle error e (in degrees) is related to the observed dec drift rate d (in degrees/hour) by Sin(e) = d / 15 . (Or is it tan()? – Won’t be much difference.)

This is because the stars are moving in RA on the celestial equator at 15 degrees per hour (360 degrees/24 hours).

Planewave Ascension 200HR Mount

The screw pitches are

• Azimuth Adjustment Knob: 1 turn = 0.4 degrees (24 arc minutes).
• Altitude Adjustment Knob: 1 turn = 0.5 degree (30 arc minutes)

References

www.jimsmobile.com/html_docs/polar-alignment.htm

www.actonastro.com/polar.htm