Meade 60EQ-A Lining UP with the Celestial Pole, Polar Alignment of the Equatorial Mount, See Fig

– 8 –

(also known as “M57”) by its Right Ascension (18hr) and its

Declination (+33°).

North

Celestial

+90° Déc.

Pole

■ Right Ascension (R.A.): This celestial version of longitude is

(Vicinity of

Star

Polaris)

measured in units of hours (hr), minutes (min), and seconds

Celestial

D

(sec) on a 24-hour "clock" (similar to how Earth's time zones

Equator

e

c

l

i

n

a

are determined by longitude lines). The "zero" line was

t

i

o

13

12

11

n

15

14

10

arbitrarily chosen to pass through the constellation Pegasus, a

9

8

17

16

Rotation

7

sort of cosmic Greenwich meridian. R.A. coordinates range

18

6

19

of the

5

20

Earth

4

from 0hr 0min 0sec to 23hr 59min 59sec. There are 24 primary

3

21

22

2

23

0

1

0

°

Dec.

lines of R.A., located at 15-degree intervals along the celestial

Right

equator. Objects located further and further East of the zero

Ascension

R.A. grid line (0hr 0min 0sec) carry higher R.A. coordinates.

See Fig. 8.

South

-90°Dec.

■ Declination (Dec.): This celestial version of latitude is

Celestial

Pole

measured in degrees, arc-minutes, and arc-seconds (e.g., 15°

27' 33"). Dec. locations North of the celestial equator are

Fig. 8: Celestial Sphere.

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." See Fig. 8.

As all celestial objects therefore may be located with their celestial coordinates of Right Ascension and Declination, the task of finding objects (in particular, faint objects) in the telescope is vastly simplified. The setting circles, R.A (34, Fig. 2) and Dec. (25, Fig. 2) of your telescope may be dialed, in effect, to read the object coordinates and the object found without resorting to visual location techniques. However, these setting circles only perform correctly if the telescope is properly aligned with the North Celestial Pole.

LINING UP WITH THE CELESTIAL POLE

Objects in the sky appear to revolve around the celestial pole. (Actually, celestial objects are essentially “fixed,” and their apparent motion is caused by the Earth’s rotation). During any 24 hour period, stars make one complete revolution about the pole, circling with the pole at the center. By lining up the telescope’s polar axis (40, Fig. 2) with the North Celestial Pole (or for observers located in Earth’s Southern Hemisphere with the South Celestial Pole), astronomical objects may be followed, or “tracked,” by moving the telescope about one axis, the polar axis.

Little Dipper	Polaris
Big Dipper	Cassiopeia

Figure 9: Finding Polaris

If the telescope is reasonably well aligned with the pole, therefore, very little use of the telescope’s Declination flexible cable control is necessary and virtually all of the required telescope tracking will be in Right Ascension. (If the telescope were perfectly aligned with the pole, no Declination tracking of stellar objects would be required whatsoever). For the purposes of casual visual telescopic observations, lining up the telescope’s polar axis to within a degree or two of the pole is more than sufficient: with this level of pointing accuracy, the telescope can track accurately by slowly turning the telescope’s R.A. flexible cable control and keep objects in the telescopic field of view for perhaps 20 to 30 minutes.

POLAR ALIGNMENT OF THE EQUATORIAL MOUNT

To line up the Meade 60EQ-A with the pole, follow this procedure:

1.Release the Azimuth lock (32, Fig. 1) of the Azimuth base, so that the entire telescope-with-mounting may be rotated in a horizontal direction. Rotate the telescope until it points due North. Use a compass or locate Polaris, the North Star (see Fig. 9), as an accurate reference for due North.

2.Level the mount, if necessary, by adjusting the heights of the three tripod legs.