Handleiding Celestron CPC Deluxe 800 HD - 11007 (pagina 22 van 50) (Engels)

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Up to this point, this manual covered the assembly and basic operation

of your CPC telescope. However, to understand your telescope more

thoroughly, you need to know a little about the night sky. This section

deals with observational astronomy in general and includes information

on the night sky and polar alignment.

>>

To help nd objects in the sky, astronomers use a celestial coordinate

system that is similar to our geographical coordinate system here on

Earth. The celestial coordinate system has poles, lines of longitude and

latitude and an equator. For the most part, these remain xed against the

background stars.

The celestial equator runs 360 degrees around the Earth and separates

the northern celestial hemisphere from the southern. Like the Earth’s

equator, it bears a reading of zero degrees. On Earth this would be

latitude. However, in the sky this is referred to as declination, or DEC for

short. Lines of declination are named for their angular distance above

and below the celestial equator. The lines are broken down into degrees,

minutes of arc and seconds of arc. Declination readings south of the

equator carry a minus sign (-) in front of the coordinate and those north

of the celestial equator are either blank (i.e., no designation) or preceded

by a plus sign (+).

The celestial equivalent of longitude is called Right Ascension, or R.A. for

short. Like the Earth’s lines of longitude, they run from pole to pole and are

evenly spaced 15 degrees apart. Although the longitude lines are separated

by an angular distance, they are also a measure of time. Each line of

longitude is one hour apart from the next. Since the Earth rotates once

every 24 hours, there are 24 lines total. As a result, the R.A. coordinates

are marked o in units of time. It begins with an arbitrary point in the

constellation of Pisces designated as 0 hours, 0 minutes, 0 seconds. All

other points are designated by how far (i.e., how long) they lag behind this

coordinate after it passes overhead moving toward the west.

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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 lm

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.)

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Celestron CPC Deluxe 800 HD - 11007 Handleiding

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