Manual Celestron POWERSEEKER 80 EQ - 21048 (page 8 of 19) (English)

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Motion of the Stars

The daily motion of the Sun across the sky is familiar to even the most casual observer. This daily trek is not the Sun

moving as early astronomers thought, but the result of the Earth's rotation. The Earth's rotation also causes the stars to do the

same, scribing out a large circle as the Earth completes one rotation. The size of the circular path a star follows depends on

where it is in the sky. Stars near the celestial equator form the largest circles rising in the east and setting in the west.

Moving toward the north celestial pole, the point around which the stars in the northern hemisphere appear to rotate, these

circles become smaller. Stars in the mid-celestial latitudes rise in the northeast and set in the northwest. Stars at high

celestial latitudes are always above the horizon, and are said to be circumpolar because they never rise and never set. You

will never see the stars complete one circle because the sunlight during the day washes out the starlight. However, part of

this circular motion of stars in this region of the sky can be seen by setting up a camera on a tripod and opening the shutter

for a couple hours. The processed film will reveal semicircles that revolve around the pole. (This description of stellar

motions also applies to the southern hemisphere except all stars south of the celestial equator move around the south celestial

pole.)

Latitude Scales

The easiest way to polar align a

telescope is with a latitude scale.

Unlike other methods that require you

to find the celestial pole by identifying

certain stars near it, this method works

off of a known constant to determine

how high the polar axis should be

pointed (see figure 11).

The constant, mentioned above, is a

relationship between your latitude and

the angular distance the celestial pole

is above the northern (or southern)

horizon; The angular distance from

the northern horizon to the north

celestial pole is always equal to your

latitude. To illustrate this, imagine

that you are standing on the north

pole, latitude +90°. The north celestial

pole, which has a declination of +90°,

would be directly overhead (i.e., 90

above the horizon). Now, let’s say

that you move one degree south —

your latitude is now +89° and the

celestial pole is no longer directly

overhead. It has moved one degree

closer toward the northern horizon.

This means the pole is now 89° above

the northern horizon. If you move one

degree further south, the same thing

happens again. You would have to

travel 70 miles north or south to

change your latitude by one degree.

As you can see from this example, the

distance from the northern horizon to the celestial pole is always equal to your latitude.

Figure 9

All stars appear to rotate around the celestial poles. However, the appearance of this motion

varies depending on where you are looking in the sky. Near the north celestial pole the stars

scribe out recognizable circles centered on the pole (1). Stars near the celestial equator also

follow circular paths around the pole. But, the complete path is interrupted by the horizon.

These appear to rise in the east and set in the west (2). Looking toward the opposite pole, stars

curve or arc in the opposite direction scribing a circle around the opposite pole (3).

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Celestron POWERSEEKER 80 EQ - 21048 Manual

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