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Big Dipper | N.C.P. | |||
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(in Ursa Major) |
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| Polaris |
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| Cassiopeia |
Pointer |
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Stars |
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Figure 6. To find Polaris in the night sky, look north and find the Big Dipper. Extend an imaginary line from the two "Pointer Stars" in the bowl of the Big Dipper. Go about five times the distance between those stars and you'll reach Polaris, which lies within 1° of the north celestial pole (NCP).
from drifting out of your telescope’s field of view while you’re observing.
This is accomplished by slowly rotating the telescope on its right ascension (R.A.) axis, using only the R.A.
Polar Alignment
For Northern Hemisphere observers, approximate polar align- ment is achieved by pointing the mount’s R.A. axis at the North Star, or Polaris. It lies within 1° of the north celestial pole (NCP), which is an extension of the Earth’s rotational axis out into space. Stars in the Northern Hemisphere appear to revolve around the NCP.
To find Polaris in the sky, look north and locate the pattern of the Big Dipper (Figure 6). The two stars at the end of the “bowl” of the Big Dipper point right to Polaris.
Observers in the Southern Hemisphere aren’t so fortunate to have a bright star so near the south celestial pole (SCP). The star Sigma Octantis lies about 1° from the SCP, but it is barely visible with the naked eye (magnitude 5.5).
For general visual observation, an approximate polar align- ment is sufficient.
1.Level the equatorial mount by adjusting the length of the three tripod legs.
2.There are two latitude adjustment
3.Loosen the Dec. lock lever and rotate the telescope’s opti-
cal tube until it is parallel with the R.A. axis, as it is in Figure
Azimuth
fine adjustment knobs
Tripod attachment knob
Figure 7. For polar alignment, position the tripod so that the “N” label at the base of the mount faces north. The two azimuth fine adjustment knobs above it are used to make small adjustments to the mount’s azimuth position.
5. The pointer on the Dec. setting circle should read 90°. Retighten the Dec. lock lever.
4.Move the tripod so the telescope tube and R.A. axis point roughly at Polaris. If you cannot see Polaris directly from your observing site, consult a compass and rotate the tri- pod so the telescope points north. There is a label bearing a large “N” at the base of the equatorial mount (Figure 7). It should be facing north.
The equatorial mount is now polar aligned for casual observ- ing. More precise polar alignment is recommended for astro- photography.
From this point on in your observing session, you should not make any further adjustments to the latitude of the mount, nor should you move the tripod. Doing so will undo the polar align- ment. The telescope should be moved only about its R.A. and Dec. axes.
The Polar Axis Finder Scope
The AstroView Equatorial Mount features a polar axis finder scope housed inside the R.A. axis of the mount (see Figure 3). When properly aligned and used, it makes accurate polar alignment quick and easy to do. Alignment of the polar finder need only be done once, unless it gets bumped or otherwise shifts its position.
Remove the round cover cap from the front opening in the R.A. axis of the mount. Look through the polar finder at a dis- tant object during the day. Focus the polar finder so that the images and reticle are sharp by rotating the eyepiece end of the finder. Notice that the reticle pattern consists of a crosshair with a circle around the middle. On the circumference of this circle is a tiny circle; this is where Polaris will be placed for accurate polar alignment once the finder is properly aligned. Alignment of the polar finder is best done during the day, before going out into the field at night.
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