Part 3: Aligning a Telescope

In this part of the lab you will assemble and align an equatorial-mount telescope. Such a telescope spins on two axes, one of which is aligned with the rotation axis of the Earth. This means that as the stars crawl across the sky with the rotation of the Earth, you only have to move the telescope in one axis to track them.аThe right-ascension axis, or polar axis, is shown in the upper picture at right. The declination axis is shown in the lower right hand picture.

c8 raset

Polar-Aligning Your Telescope

The first step in aligning your telescope is to move the tripod mount so that its polar axis is aligned with the rotation axis of the Earth. How can you determine the orientation of Earth's rotation axis?

c8 decset

If your telescope is properly polar-aligned, when you point roughly at the North star, the declination axis should read close to ninety degrees.

Calibrating the Right Ascension Axis

The value of right ascension at a particular point in the sky in reference to you is always changing, both because the Earth is rotating with respect to the sky throughout the night, and because the Earth moves around the Sun over the course of the year. You need to set the setting circle on your telescope's right ascension axis аfor the sky's current position so that you can use it to point to objects in the sky using their coordinates.

Choose a star that is currently above the horizon and near the celestial equator. Find the right ascension coordinates of this star. Now, point your telescope at the star and move the setting circle so that the correct right ascension is indicated. Now your telescope should be properly aligned.

Your instructor will check that you have properly set up and aligned your telescope. Once you have completed this section of the lab and your instructor has initialed your worksheet, disassemble your telescope before continuing to the rest of the lab.

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