Rough polaraxis alignment without sighting stars

If you can see Polaris in the sky, you can skip this section and go directly to the next one. If, however, you are setting up your mount in daylight, proceed as follows to get it roughly aligned.

Find true north by using a compass and correcting for magnetic declination (p. 26). Orient the mount so that the polar axis points north. Adjust the tilt of the wedge ("latitude" or "altitude") to match your latitude (Figure 4.4). For example, in New York, at latitude 40°, the baseplate should be 40° from vertical.

1 This entire book, and especially this chapter, is written for observers in the Northern Hemisphere. South of the equator, everything works in the opposite direction, and instead of Polaris, you have to sight on the much fainter star a Octantis.

Using equatorial mounts and wedges

Polar axis Y

Angle = observer's latitude

(indicated

Figure 4.4. Setting up an equatorial mount when you cannot see Polaris.

Angle = observer's

True north

(not magnetic north)

latitude

(indicated on wedge)

Level this surface

(base of wedge)

Figure 4.4. Setting up an equatorial mount when you cannot see Polaris.

With larger wedges, this is easy because latitudes are marked on the wedge itself, and there is a bubble level on the base. If the only bubble level is on the telescope (as with the Meade ETX-90), you can level the tripod in altazimuth mode, then incline the base to the appropriate angle (Figure 4.5).

Then refine the alignment by sighting on Polaris and/or by using the drift method (p. 49). Note that in the daytime, you can use the drift method on a bright star; stars down to second or third magnitude are visible in the telescope at high magnification. You can also use the drift method on planets, but not the Moon, whose orbital motion is fast enough to interfere.

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