Orion 70MM AZ instruction manual Light Pollution, Tracking Celestial Objects, Eyepiece Selection

Light Pollution

Most of us live where city lights interfere with our view of the heavens. As our metropolitan areas have become more developed, the scourge of light pollution has spread, washing out many stars and nonstellar celestial objects from our sight. Faint deep sky objects become difficult or impossible to see through the murk of light pollution. Even bright nebulas like the Orion and Lagoon Nebulas lose much of their delicate detail. The Moon and planets are not affected; they require steady air more than dark skies, so they remain good targets for city-dwelling observers.

The International Dark-Sky Association is waging the fight against light pollution. The IDSA was founded in 1988 with the mission of educating the public about the adverse impact that light pollution has on the night sky and astronomy. Through educational and scientific means, the nonprofit IDA works to raise awareness about the problem and about measures that can be taken to solve it.

Do you need help dealing with local officials to control street or building lighting in your area? The IDA’s exten- sive support materials can show you how. Help pre- serve dark skies, join the IDA today! For information, write to IDA, 3225 N. First Ave., Tuscon, AZ 85719-2103 or visit their website: www.darksky.org.

The best way to avoid immediate problems with light pol- lution, however, is to take you telescope to where there are dark skies. You will be amazed at how many stars you can see when you get away from the city lights.

tend to scatter light, which reduces an object’s brightness. Transparency­ is judged by the magnitude of the faintest stars you can see with the unaided eye (6th magnitude or fainter is desirable).

If you cannot see stars of magnitude 3.5 or dimmer then con- ditions are poor. Magnitude is a measure of how bright a star is—the brighter a star is, the lower its magnitude will be. A good star to remember for this is Megrez (mag. 3.4), which is the star in the “Big Dipper” connecting the handle to the “dip- per”. If you cannot see Megrez, then you have fog, haze, clouds, smog, or other conditions that are hindering your viewing (Figure 8).

Tracking Celestial Objects

The Earth is constantly rotating about its polar axis, complet- ing one full rotation every 24 hours; this is what defines a “day”. We do not feel the Earth rotating, but we can still tell that it is at night by seeing the apparent movement of stars from east to west.

When you observe any astronomical object, you are watching a moving target. This means the telescope’s position must be continuously adjusted over time to keep an object in the field of view. When viewing the with the Observer 70, you will need to give the optical tube (1) a light tug or push in azimuth (left

Figure 8. Megrez connects the Big Dipper’s handle to it’s “pan”. It is a good guide to how conditions are. If you can not see Megrez (a 3.4 mag star) then conditions are poor.

Figure 9. The 25mm and 10mm Explorer II eyepieces.

or right) as well as an occasional turn of the altitude micro- motion thumbwheel (13) to keep the object in the field of view. Make certain the azimuth lock knob (20) is slightly loosened before moving the scope in azimuth. Objects will appear to move faster at higher magnifications because the field of view is narrower.

Remember that objects are reversed left to right in refractor telescopes, so when you move the telescope in one direction in azimuth, the object will move in the opposite direction in the eyepiece. This takes some getting used to, but becomes sec- ond nature after a few nights out with the telescope.

Eyepiece Selection

By using eyepieces of different focal lengths, it is possible to attain many magnifications or powers with the Observer 70. Your telescope comes with two Explorer II eyepieces (Figure 9): a 25mm, which gives a magnification of 28x, and a 10mm, which gives a magnification of 70x. Other eyepieces can be used to achieve higher or lower powers. It is quite common for an observer to own five or more eyepieces to access a wide range of magnifications.

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