APPENDIX A: EQUATORIAL (POLAR) ALIGNMENT

Fig. 26: Tripod set in Polar configuration on optional #883 tripod.

Polar Alignment

The great majority of ETX-60AT and ETX-70AT owners will find it unnecessary ever to Polar align the telescope. With these ETX telescope models the standard-equipment Autostar controller allows the telescope to be used in the altazimuth (Alt/Az) orientation for all observing purpose. This section is included only for educational purposes, where the observer might wish to operate the analog set- ting circles (13 and 17, Fig.1) in place of the digi- tal setting circles built into the Autostar hand con- troller. Absent a desire to use the analog circles or simply to be informed about the use of the equato- rial (Polar-aligned) mount, reading of this appendix may be omitted.

North

 

 

 

 

 

 

 

 

 

 

Celestial

 

 

 

+90

Dec.

 

 

 

 

Pole

 

 

 

 

 

 

Star

 

 

(Vicinity

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

of Polaris)

 

 

 

 

e

 

 

 

 

 

 

 

 

 

 

 

 

D

 

 

 

 

 

 

 

 

 

 

 

 

c

 

 

 

1

 

 

 

 

 

 

 

l

 

 

 

 

 

 

 

 

 

 

a

 

 

 

 

 

 

 

 

 

 

 

i

 

 

 

 

 

 

 

 

 

 

 

n

 

 

 

 

 

 

 

 

 

 

 

 

t

 

 

 

 

 

 

 

 

 

 

 

 

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14

13

12

11

10

o

 

 

 

 

 

 

15

n

 

 

 

17 16

 

 

 

 

 

9

8

 

 

Earth’s

 

 

 

 

7

18

 

 

Rotation

 

 

 

 

 

 

6

19

 

 

 

 

 

4

5

20

21

 

 

 

 

2

3

 

Celestial

22

23

0

1

 

 

 

 

 

 

 

 

 

Equator

Right Ascension

 

 

 

 

 

 

 

 

 

 

 

 

0 Dec.

 

 

 

 

 

 

 

 

 

 

 

 

2

South

Celestial

Pole -90 Dec.

Fig. 27: Celestial Sphere.

In Polar Alignment, the telescope is oriented so that the horizontal and vertical axes of the tele- scope are lined up with the celestial coordinate system. Polar Alignment requires the telescope to be mounted to the optional #883 Deluxe Field Tripod (Fig. 26).

In order to Polar 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 introduc- tion to the terminology of Polar-aligned astronomy, and includes instructions for finding the celestial pole and for finding objects in the night sky using Declination and Right Ascension.

Celestial Coordinates

Celestial objects are mapped according to a coordinate system on the Celestial Sphere (Fig. 26), an imaginary sphere surrounding Earth on which all stars appear to be placed. This celestial object mapping system is analogous to the Earth-based coordinate system of latitude and longitude.

The poles of the celestial coordinate system are defined as those two points where the Earth’s rotational axis, if extended to infinity, North and South, intersect the celestial sphere. Thus, the North Celestial Pole (1, Fig. 27) is that point in the sky where an extension of the Earth’s axis through the North Pole intersects the celestial sphere. This point in the sky is located near the North Star, Polaris.

In mapping the surface of the Earth, lines of longitude are drawn between the North and South Poles. Similarly, lines of latitude are drawn in an East-West direction, parallel to the Earth’s Equator. The Celestial Equator (2, Fig. 27) is a projection of the Earth’s Equator onto the celes- tial sphere.

Just as on the surface of the Earth, in mapping the celestial sphere, imaginary lines have been drawn to form a coordinate grid. Thus, object positions on the Earth’s surface are specified by their latitude and longitude. For example, you could locate Los Angeles, California, by its lati- tude (+34°) and longitude (118° West); similarly, you could locate the constellation Ursa Major (which includes the Big Dipper) by its general position on the celestial sphere:

R.A.: 11hr; Dec: +50°.

Right Ascension: The celestial analog to Earth longitude is called “Right Ascension,” or “R.A.,” and is measured in time on the 24 hour “clock” and shown in hours or “hr," minutes or “min," and seconds or “sec," from an arbitrarily defined “zero” line of Right Ascension passing through the constellation Pegasus. Right Ascension coordinates range from 0hr 0min 0sec to 23hr 59min 59sec. Thus 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 prime Right Ascension grid line, 0hr 0min 0sec, carry increasing R.A. coordinates.

Declination: The celestial analog to Earth latitude is called Declination, or “Dec,” and is measured in degrees, arc-minutes and arc-seconds, e.g., 15° 27' 33". Declination shown as North of the celestial equator is indicated with a “+” sign in front of the measurement,

Appendix A 31

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Image 31
Meade ETX-70AT instruction manual Appendix a Equatorial Polar Alignment, Celestial Coordinates

ETX-70AT specifications

The Meade ETX-70AT is a compact, portable telescope that caters to both amateur astronomers and educational purposes. This telescope is part of the renowned ETX series, known for its innovative features and user-friendly design. With an aperture of 70mm, the ETX-70AT is designed to provide clear, bright images of celestial objects, making it an ideal choice for novice astronomers eager to explore the night sky.

One of the standout features of the ETX-70AT is its Maksutov-Cassegrain optical design. This design combines a Maksutov corrector plate with a compact cassegrain layout, allowing for a shorter tube length while still providing excellent optical performance. As a result, users can easily transport the telescope to various observing locations without compromising on image quality.

The telescope boasts a focal length of 350mm, which offers a wide field of view, allowing observers to comfortably locate and track celestial phenomena. The ETX-70AT comes equipped with a built-in electronic control system known as the Audio Star, featuring a database of over 30,000 celestial objects. This system not only makes it easier for users to locate specific targets but also enhances the overall observing experience by providing informative audio commentary about different astronomical objects.

Another notable characteristic is its lightweight design, weighing in at just around 5 lbs. This portability factor makes it an excellent choice for stargazers who prefer to travel or hike to optimal viewing locations. The telescope is mounted on an adjustable and stable aluminum tripods, providing a solid foundation for viewing.

The Meade ETX-70AT also includes a variety of accessories, including two eyepieces (26mm and 9.7mm), a finder scope to help users aim accurately, and a variety of optional filters to enhance viewing contrast and clarity. Furthermore, the telescope supports direct connection to a computer for astrophotography, enabling enthusiasts to capture their astronomical observations digitally.

In summary, the Meade ETX-70AT is an exceptional entry-level telescope that combines portability, advanced technology, and ease of use. With its powerful optics, automated features, and impressive accessory offerings, it serves as an excellent tool for any individual or educational institution looking to delve into the wonders of astronomy.