Meade-instruments LX600 User Manual download pdf (Page 57)

Appendix E

APPENDIX E: EQUATORIAL

(POLAR) ALIGNMENT

Equatorial Alignment

In equatorial (or “polar”) alignment, the telescope is oriented so

that the horizontal and vertical axes of the telescope are lined up

with the celestial coordinate system.

Important Note: The “Telescope: Mount”option of the Setup

menu is set to “Alt-az” as the default mount by the factory.

The example presented in this section assumes that you

are performing an alignment procedure for the ﬁ rst time

with your telescope and therefore, the “Telescope: Mount”

option does not need to be selected.

If the telescope is equatorially mounted, you must choose the

“Polar” option from the AutoStar II “Telescope Mount” menu.

In order to equatorial align your telescope, it is essential to have

an understanding of how and where to locate celestial objects

as they move across the sky. This section provides a basic

introduction to the terminology of equatorial-aligned astronomy,

and includes instructions for ﬁ nding the celestial pole and

for ﬁ nding objects in the night sky using Declination and

Right Ascension.

Celestial Coordinates

A celestial coordinate system was 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 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

deﬁ ned as those two points where the Earth’s North and South

poles (i.e., the Earth’s axis), if extended to inﬁ nity, would cross

the celestial sphere. Thus, the North Celestial Pole (Fig. 19, 1)

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 (Fig. 19, 1). The celestial

equator (Fig. 19, 2) 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 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 (RA): 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. RA coordinates range

from 0hr 0min 0sec to 23hr 59min 59sec.

There are 24 primary lines of RA, located at

15-degree intervals along the celestial equator.

Objects located further and further East of the

zero RA grid line (0hr 0min 0sec) carry higher

RA 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".

Fig. 19. Celestial Sphere.

1 2 ... 52 53 54 55 56 57 58 59 60 61 62 ... 71 72

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Meade-instruments LX600 User Manual Page 57

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