Orion 6/6I Tracking Celestial Objects, Eyepiece Selection, Telescope Focal Length mm

Figure 20. Megrez connects the Big Dipper’s “handle” to its “pan.” If you cannot see Megrez, a magnitude 3.4 star, then the viewing conditions are poor.

seeing affects images at high powers more severely. Planetary observing may also be poor.

In conditions of good seeing, star twinkling is minimal and images appear steady in the eyepiece. Seeing is best over- head, worst at the horizon. Also, seeing generally gets better after midnight, 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).

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 the star, the lower its magnitude. A good star to remember for this is Megrez (mag. 3.4), which is the star in the “Big Dipper” that connects the “handle” to the “pan” of the dipper (Figure 20). If you cannot see Megrez, then you have fog, haze, clouds, smog, or other conditions (such as light pol- lution) that are hindering your viewing.

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 see it at night from the apparent movement of stars from east to west.

When you observe any astronomical object, you are in essence watching a moving target. This means the telescope’s position must be continuously adjusted over time to keep the object in the field of view. This is easy to do with the StarBlast 6/6i because of its smooth motions on both axes. As the object moves off towards the edge of the field of view, just lightly nudge the telescope to re-center it.

Objects appear to move across the field of view faster at high- er magnifications. This is because the field of view becomes narrower.

Eyepiece Selection

By using eyepieces of different focal lengths, it is possible to attain many magnifications, or powers, with the StarBlast 6/6i. Your telescope comes with two Sirius Plössl eyepieces of dif- ferent focal lengths: a 25mm, which provides a magnification of 30x, and a 10mm, which yields 75x. Other eyepieces can be used to achieve higher or lower powers. It is quite common for an observer to own many eyepieces to access a wide range of magnifications.

To calculate the magnification of a telescope-eyepiece com- bination, simply divide the focal length of the telescope by the focal length of the eyepiece.

Telescope Focal Length (mm)	= Magnification
Eyepiece Focal Length (mm)

For example, the StarBlast 6, which has a focal length of 750mm, used in combination with the 25mm eyepiece, yields a magnification of

750mm	= 30x
25mm

Whatever you choose to view, always start by inserting your lowest-power (longest focal length) eyepiece to locate and center the object. Low magnification yields a wide field of view, which shows a larger area of sky in the eyepiece. This makes finding and centering an object much easier. Trying to find and center objects with a high-power (narrow field of view) eye- piece is like trying to find a needle in a haystack!

Once you’ve centered the object in the eyepiece, you can switch to a higher magnification (shorter focal length) eye- piece, if you wish. This is recommended for small and bright objects, like planets and double stars. The Moon also takes higher magnifications well.

The best rule of thumb with eyepiece selection is to start with

alow-power, wide-field eyepiece, and then work your way up in magnification. If the object looks better, try an even higher magnification eyepiece. If the object looks worse, then back off the magnification a little by using a lower-power eyepiece.

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, phases 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 faint deep-sky objects, except in a few of the brightest ones.

Remember that you are seeing these objects with your own eyes in real time, using your own telescope! That beats looking at a picture in a book or on a computer screen, in our opinion. Each session with your telescope will be a learning experi- ence. Each time you work with your telescope it will get easier to use, and celestial objects will become easier to find. There is a big difference between looking at a well-made, full-color NASA image of a deep-sky object in a lit room during the day- time, and seeing that same object in your telescope at night.

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