Orion 9884 instruction manual Setting Up and Using the Equatorial Mount, Polar Alignment

faint. Many observers own at least one 2" eyepiece in order to achieve the widest field of view possible for deep sky-observ- ing. The expansive view will make you feel like you’re floating in space!

To use 2" eyepieces, simply loosen the thumb screw on the star diagonal that secures the 1.25" adapter, and remove the adapter. Insert a 2" eyepiece directly into the diagonal, and secure it in place with the thumb screw on the diagonal. You are now ready to observe with the 2" eyepiece. If you attempt to place a 2" eyepiece directly into the focuser drawtube with- out using the star diagonal, images will not come into focus. If you wish to view with 2" eyepieces without using the diagonal, you will need to purchase an optional 2" extension tube.

Note About Chromatic Aberration

Chromatic aberration literally means color distortion. Whenever light passes through one material to another, light of differ- ent wavelengths (color) is bent by different amounts. This is

aproblem that plagues refractor-type telescopes, since light passes through both air and glass to form an image. Most astronomical objects emit a spectrum comprised of many dif- ferent wavelengths of light, so each wavelength will be bent by a slightly different amount when passing through a lens. This results in each color of light reaching precise focus at a slightly different point, which will provide unacceptable images.

The 80mm ED is designed to minimize chromatic aberration. The objective lens is actually comprised of two individual lens- es, called elements, one of which is made of ED (Extra-low Dispersion) glass, a special type of glass that has superior refractive properties when compared to normal types of glass. The use of this ED glass minimizes the amount of chromatic aberration, resulting in a much more pleasing view when com- pared to telescopes that do not use ED glass.

6.Setting Up and Using the Equatorial Mount

When you look at the night sky, you no doubt have noticed that the stars appear to move slowly from east to west over time. That apparent motion is caused by the Earth’s rotation (from west to east). An equatorial mount (Figure 8) is designed to compensate for that motion, allowing you to easily “track” the movement of astronomical objects, thereby keeping them from drifting out of your telescope’s field of view while you’re observing.

This is accomplished by slowly rotating the telescope on its right ascension (R.A.) axis, using only the R.A. slow-motion knob. But first the R.A. axis of the mount must be aligned with the Earth’s rotational (polar) axis - a process called polar align- ment.

Polar Alignment

For Northern Hemisphere observers, approximate polar align- ment is achieved by pointing the mount’s right ascension axis

	Little Dipper
	(in Ursa Minor)
Big Dipper	N.C.P.
(in Ursa Major)		Polaris
Pointer		Cassiopeia
Stars

Figure 9. To find Polaris in the night sky, look north and find the Big Dipper. Extend an imaginary line from the two "Pointer Stars" in the bowl of the Big Dipper. Go about five times the distance between those stars and you'll reach Polaris, which lies within 1° of the north celestial pole (NCP).

R.A. setting circle

Polar axis finder scope (optional)

Latitude scale (opposite side)

Latitude adjustment L-bolts

AscensionRight

Axis

Declination

Axis

Figure 8. The SkyView Pro mount.

Dec. slow-motion control knob

Dec. setting circle

Dec. lock lever

Front opening

R.A. lock lever

R.A. slow-motion control knob

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