The¬†below photo is of an equatorial mount that I¬†designed and built¬†many years ago. This device is equipped with a clock drive (from Edmond Scientific) which counteracts the earth’s rotation and allows me to take time exposures of the nighttime sky. Unfortunately, light pollution where I live¬†makes¬†astrophotography problematic.¬†So my current goals are rather modest.

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Equatorial mount alignment (getting the mount’s axis parallel to the earth’s).

The optimal way to align the mount is to point the axis of rotation at the North Celestial Pole (NCP) using a built in sight and the North Star.

The following describes an approach for when the North Star (Polaris) is obscured and can not be used.

Adjusting for observer’s latitude:

If the mount were located on the Equator, then Polaris would be on the horizon and the axis pointed at it would be horizontal. At this point the adjusted level would form a 90 degree angle with it’s supporting post.

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If the mount were moved to my location, at 40 degrees north, Polaris would move up to 40 degrees¬†above the horizon. The adjusted level would now form a 50 degree angle (90-40=50) with it’s supporting post.

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Finding North:

The Equation of  Time (http://www.ppowers.com/EoT.htm) was used to determine when the sun would be directly south on a given day. The photo taken (on a window sill) at the specified time shows that my house is facing about 3 degrees east of south.  Since the house almost faces south it can be used as a fairly accurate guide from points in my yard where Polaris is obscured.

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Another day, when the sun was directly to the south, a level was turned so that it cast no shadow. The level was then used as a straight edge, and a north/south line was drawn.

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The below photo shows that magnetic north (from where I live) is a little more than 10 degress west of true north. This number agrees with the magnetic declination given by a magnetic field calculator site (http://www.ngdc.noaa.gov/geomag-web/?id=declinationFormId).

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The following photo shows the level and compass combination which allows me to align my equatorial mount independent of the North Star.

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