Bedienungsanleitung Meade Goto-Kit for equatorial EQ-5 Mounts (Seite 29 von 40) (Englisch)

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Instruction Manual

A celestial coordinate system was created that maps an imaginary sphere sur-

rounding the Earth upon which all stars appear to be placed. This mapping sys-

tem is similar to the system of latitude and longitude on Earth surface maps.

In mapping the surface of the Earth, lines of longitude are drawn between the

North and South Poles and lines of latitude are drawn in an East-West direction,

parallel to the Earth’s equator. Similarly, imaginary lines have been drawn to form

a latitude and longitude grid for the celestial sphere. These lines are known as

Right Ascension and Declination.

The celestial map also contains two poles and an equator just like a map of

the Earth. The poles of this coordinate system are defined as those two points

where the Earth’s north and south poles (i.e., the Earth‘s axis), if extended to

infinity, would cross the celestial sphere. Thus, the North Celestial Pole (1, Fig.

41) is that point in the sky where an extension of the North Pole intersects the

celestial sphere. The North Star, Polaris is located very near the North Celestial

Pole. The celestial equator (2, Fig. 41) is a projection of the Earth’s equator onto

the celestial sphere.

Just as an object‘s position on the Earth’s surface can be located by its latitude

and longitude, celestial objects may also be located using Right Ascension and

Declination. For example, you could locate Los Angeles, California, by its latitude

(+34°) and longitude (118°). Similarly, you could locate the Ring Nebula (M57) by

its Right Ascension (18hr) and its Declination (+33°).

• Right Ascension (R.A.): This celestial version of longitude is measured in

units of hours (hr), minutes (min), and seconds (sec) on a 24-hour „clock“

(similar to how Earth‘s time zones are determined by longitude lines). The

„zero“ line was arbitrarily chosen to pass through the constellation Pegasus

— a sort of cosmic Greenwich meridian. R.A. coordinates range from 0hr

0min 0sec to 23hr 59min 59sec. There are 24 primary lines of R.A., located

at 15-degree intervals along the celestial equator. Objects located further

and further East of the zero R.A. grid line (0hr 0min 0sec) carry higher R.A.

coordinates.

• Declination (Dec.): This celestial version of latitude is measured in degrees,

arc-minutes, and arc-seconds (e.g., 15° 27‘ 33“). Dec. locations north of

the celestial equator are indicated with a plus (+) sign (e.g., the Dec. of the

North celestial pole is +90°). Dec. locations south of the celestial equator

are indicated with a minus (–) sign (e.g., the Dec. of the South celestial pole

is –90°). Any point on the celestial equator (such as the the constellations of

Orion, Virgo, and Aquarius) is

said to have a Declination of zero, shown as

0° 0‘ 0.“

Setting Circles

Setting circles included with the LXD™75 Newtonians permit the location of faint

celestial objects not easily found by direct visual observation. With the telescope

pointed at the North Celestial Pole, the Dec. circle (3, Fig. 1a) should read 90°

(understood to mean +90°). Each division of the Dec. circle represents a 1° incre-

ment. The R.A. circle (15, Fig. 1a) runs from 0

to (but not including) 24

, and

reads in increments of 5

min

Using setting circles requires a developed technique. When using the circles for

the first time, try hopping from one bright star (the calibration star) to another

bright star of known coordinates. Practice moving the telescope from one easy-

to-find object to another. In this way, the precision required for accurate object

location becomes evident.

Note You may also enter an object‘s R.A. and Dec. coordinates using

the „User: Objects“ option of handbox‘s Object menu. The handbox

then automatically slews the telescope to the entered coordinates.

To use the setting circles to locate an object not easily found by direct

visual observation:

Insert a low-power eyepiece, such as a 26mm, into the focuser assembly. Pick

out a bright star with which you are familiar (or is easily located) that is in the area

of the sky in which your target object is located. Look up the R.A. coordinate of

the bright star, and also of the object you wish to locate, in a star atlas. Point

Rotazione

Terrestre

0 Dec.

Polo Sud

Celeste

Ascensione retta

Stella

Equatore

Celeste

-90 Dec.

+90 Dec.

Polo Nord Celeste

(vicino alla Polare)

Fig. 41: Celestial Sphere.

Appendix A:

Celestial coordinates

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