Meade DS-2000 Series Bedienerhandbuch PDF herunterladen (Seite 35)

Celestial Coordinates

It is helpful to understand how to locate celestial

objects as they move across the sky.

A celestial coordinate system w

as created that

maps an imaginary sphere surrounding the Earth

upon which all stars appear to be placed. This

mapping system is similar to the system of latitude

and longitude on Earth surface maps.

In mapping the surface of the Earth, lines of longi-

tude 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 on the celestial

sphere. These lines are known as

Right

Ascension

and Dec

lination

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 tw

o points where the Earth’s north and

south poles (i.e

the Ear

th's axis), if extended to infinity, would cross the celestial sphere. Thus,

the North Celestial Pole (

1, Fig. 30) is that point in the sky where an extension of the North Pole

intersects the celestial sphere. This point in the sky is located very near the North Star, Polaris.

The celestial equator (

2, Fig. 30) is a projection of the Earth’s equator onto the celestial sphere.

So just as an object's position on the Earth’s surface can be located by its latitude and longi-

tude, celestial objects may also be located using Right Ascension and Declination. For exam-

ple, you could locate Los Angeles, California, by its latitude (+34°) and longitude (118°).

Similarly, you could locate the constellation Ursa Major (the Big Dipper) by its Right Ascension

(11hr) and its Declination (+50°).

•

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 con-

stellation 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 (Altitude): This celestial version of latitude is measured in degrees, minutes,

and seconds (e.g., 15°

27' 33"). Dec. locations north of the celestial equator are indicated with

a plus (+) sign (

.g.,

the Dec.

of the Nor

th celestial pole is +90

Dec. locations south of the

celestial equator are indicated with a min

us (–) sign (

.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

Aquar

ius) is

said to ha

e a Declination of z

ero

, sho

wn as 0° 0' 0."

Locating the Celestial Pole

o get basic bear

ings at an obser

ving location, take note of where the Sun rises (East) and sets

(West) each day. After the site is dark, face North by pointing your left shoulder toward where

the Sun set. To precisely point at the pole, find the North Star (Polaris) by using the Big Dipper

as a guide (

Fig. 31).

IMPORTANT NOTE: For almost all astro-

nomical observing requirements, approxi-

mate settings are acceptable. Do not allow

undue attention to precise alignment of the

telescope to interfere with your basic

enjoyment of the instrument.

Earth’s

Rotation

0 Dec.

South 

Celestial 

Pole

Right Ascension

Star

Celestial 

Equator

-90 Dec.

+90 Dec.

orth 

Celestial 

Pole

(

Vicinity 

of Polaris)

Fig. 30: Celestial Sphere.

APPENDIX A

Polaris

Little Dipper

Big Dipper

Cassiopeia

Fig. 31: Locating Polaris.

1 2 ... 30 31 32 33 34 35 36 37 38 39 40 ... 47 48

Kommentare zu diesen Handbüchern

Keine Kommentare

Meade DS-2000 Series Bedienerhandbuch Seite 35

Kommentare zu diesen Handbüchern

Verwandte Produkte und Handbücher für Teleskope Meade DS-2000 Series