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Using an Equatorial Mount for Astronomy

EQ Mount

EQ Mount

Both Telescopes and satellite dishes, often rely on equatorial mounts to remain focused on an object in the sky with a diurnal motion. In fact, many photographers also use equatorial mounts as well. The alternative is the tedium of re-locating the target every time the instrument is used.

This involves two axes: equatorial (right ascension) and perpendicular (declination). Right ascension corresponds to the polar axis; declination refers to how far off the celestial equator an object is. The Pole star is nearly 90 degrees declination, which is why it’s commonly used for orientation.

Clock Drives

These are normally used with the equatorial axis, rotating the instrument to synchronize with the apparent diurnal motion of the sky. A satellite in geosynchronous orbit would not need to be tracked, since it never changes orientation relative to the stationary ground observer. A star, in contrast, appears to move across the sky as the Earth rotates.

Equatorial mounts come in various designs, modern ones generally supplemented with computerized object location. One main type uses digital setting circles and a microcomputer with an object database attached to encoders. The computer monitors the telescope’s position and the operator manually adjusts the telescope.

Setting Circles

These are used when the object’s coordinates are known, based on star charts and tables of stellar objects. Once a telescope is polar-aligned, a known star close to the one being sought is located. To be useful, it should be easy to spot and listed in a catalog or star chart.

The orientation star’s coordinates can be looked up or calculated from a star chart. The more accurate the coordinates, the easier the task of finding the target star. Setting circles are then moved to match values obtained for the target star.

If the declination setting circle requires correction, it is not polar-aligned or the declination axis has slipped around its holder and needs to be adjusted.

Without a permanent observatory, the ascension axis probably needs correction. Then the disk(s) are rotated so that the correct values match the object on the telescope.

At this point, simply look up the coordinates of the target object and move the telescope so that its coordinates match those of the target.

Look up coordinates of the target star. If the telescope and setting circles have been aligned precisely, the target should be in view.

Quality Telescope Mounts

Orion Telescopes and Binoculars, in business since 1975, is billed as “America’s largest direct source for quality outdoor optics.” One of their more interesting equatorial mounts is the Atlas EQ-G. It’s pricey for the casual hobbyist, running over $1000, but once oriented, the operator can select from 42,900 objects and have the mount automatically find them. In other words, let the computer do the work. It’s a lot more fun.

Orion SkyView Pro Equatorial GoTo Telescope MountOrion SkyView Pro Equatorial GoTo Telescope Mount Orion Atlas EQ-G Computerized GoTo Telescope MountOrion Atlas EQ-G Computerized GoTo Telescope Mount

Orion StarSeeker IV GoTo Altazimuth Mount & Tripod