Cooling the Telescope, Let Your Eyes Dark-Adapt

when much of the heat absorbed by the Earth during the day has radiated off into space.

Especially important for observing faint objects is good “trans- parency”—air free of moisture, smoke, and dust. All tend to scat- ter 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).

Cooling the Telescope

All optical instruments need time to reach “thermal equilibri- um.” The bigger the instrument and the larger the temperature change, the more time is needed. Allow at least 30 minutes for your telescope to acclimate to the temperature outdoors.

Let Your Eyes Dark-Adapt

Don’t expect to go from a lighted house into the darkness of the outdoors at night and immediately see faint nebulas, galaxies, and star clusters—or even very many stars, for that matter. Your eyes take about 30 minutes to reach perhaps 80% of their full dark-adapted sensitivity. As your eyes become dark-adapted, more stars will glimmer into view and you’ll be able to see fainter details in objects you view in your telescope.

To see what you’re doing in the darkness, use a red-filtered flash- light rather than a white light. Red light does not spoil your eyes’ dark adaptation like white light does. A flashlight with a red LED light is ideal, or you can cover the front of a regular incandescent flashlight with red cellophane or paper. Beware, too, that nearby porch, streetlights, and car headlights will ruin your night vision.

Eyepiece Selection

Magnification, or power, is determined by the focal length of the telescope and the focal length of the eyepiece being used. Therefore, by using eyepieces of different focal lengths, the resultant magnification can be varied. It is quite common for an observer to own five or more eyepieces to access a wide range of magnifications. This allows the observer to choose the best eyepiece to use depending on the object being viewed and view- ing conditions. The StarBlast 4.5 EQ comes with two eyepieces, which will suffice nicely to begin with.

Magnification is calculated as follows:

The maximum attainable magnification for a telescope is directly related to how much light it can gather. The larger the aperture, the more magnification is possible. In general, a figure of 60x per inch of aperture is the maximum attainable for most tele- scopes.Your StarBlast 4.5 EQ has an aperture of 4.5 inches, so the maximum magnification would be about 270x. This level of magnification assumes you have ideal conditions for observing.

Keep in mind that as you increase magnification, the brightness of the object viewed will decrease; this is an inherent principle of the laws of physics and cannot be avoided. If magnification is doubled, an image appears four times dimmer. If magnification is tripled, image brightness is reduced by a factor of nine!

Start by centering the object you wish to see in the 15mm eye- piece. Then you may want to increase the magnification to get a closer view. If the object is off-center (i.e., it is near the edge of the field of view) you will lose it when you increase magnification, since the field of view will be narrower with the higher-powered eyepiece.

To change eyepieces, first loosen the securing thumbscrews on the focuser drawtube. Then carefully lift the eyepiece out of the drawtube. Do not tug or pull the eyepiece to the side, as this will knock the telescope off its target. Replace the eyepiece with the new one by sliding it gently into the drawtube. Re-tighten the thumbscrews, and refocus for your new magnification.

What to Expect

So what will you see with your telescope? You should be able to see bands on Jupiter, the rings of Saturn, craters on the Moon, the waxing and waning of Venus, and many bright deep-sky objects. Do not expect to see color as you do in NASA photos, since those are taken with long-exposure cameras and have “false color” added. Our eyes are not sensitive enough to see color in deep-sky objects except in a few of the brightest ones.

Objects to Observe

Now that you are all set up and ready to go, one critical decision must be made: what to look at?

A.The Moon

With its rocky surface, the Moon is one of the easiest and most interesting objects to view with your telescope. Lunar craters, marias, and even mountain ranges can all be clearly seen from a distance of 238,000 miles away! With its ever-changing phas- es, you’ll get a new view of the Moon every night. The best time

Telescope Focal Length (mm)

Eyepiece Focal Length (mm)

= Magnification

to observe our one and only natural satellite is during a partial phase, that is, when the Moon is not full. During partial phas- es, shadows are cast on the surface, which reveal more detail, especially right along the border between the dark and light por-

For example, the StarBlast 4.5 EQ has a focal length of 450mm, which when used with the supplied 15mm eyepiece yields:

450 mm = 30x

15 mm

The magnification provided by the 6mm eyepiece is:

	450 mm	= 75x
	6 mm	= 75x
	6 mm

tions of the disk (called the “terminator”). A full Moon is too bright and devoid of surface shadows to yield a pleasing view. Make sure to observe the Moon when it is well above the horizon to get the sharpest images.

Use an optional Moon filter to dim the Moon when it is very bright. It simply threads onto the bottom of the eyepieces (you must first remove the eyepiece from the focuser to attach a fil- ter).You’ll find that the Moon filter improves viewing comfort, and also helps to bring out subtle features on the lunar surface.