5
GLOSSARY
Altazimuth mount
- the simplest type of mount, with two motions: altitude (up and down) and azimuth (side-
to-side). “Mount” refers to the parts of the telescope supporting the tube, which carries all the telescope’s
optics. The mount is made up of the ground plate, or base, and the rocker box.
Altitude bearings -
used on the
Star Hopper
®
to provide an axis of rotation for altitude adjustments.
Aperture -
the diameter of the main optical element of the telescope; either the primary mirror or objective
lens. The larger the aperture, the more light the telescope collects. More light creates a brighter, sharper
image.
Barlow lens -
these lenses are optional accessories that double the magnifying power of your eyepieces by
increasing their effective focal length. For example, an 18mm eyepiece mounted on a 2x Barlow lens would
have the magnifying power of a 9mm eyepiece. It’s like having two eyepieces in one - an economical way to
increase your range of magnifications without buying new eyepieces.
Collimation
- the proper alignment of the optical elements in a telescope, which is critical to achieving
optimum results. Poor collimation results in visual aberrations and distorted images. For a full description of
how to collimate your telescope see the Collimation section of this manual.
Deep-sky objects
- celestial objects outside the boundaries of our solar system.
Extended objects
- large celestial objects, other than stars, such as nebulae and galaxies.
Field of view
- the size, in degrees, of the area you can see through the eyepiece of your telescope.
Finderscope -
a low power telescope with cross hairs mounted to the side of a higher powered telescope,
used to locate objects more easily.
Focal length -
the distance from the optical center of the lens to the point where the incoming light rays
converge, creating a clear, focused image.
Newtonian reflecting telescope
- generally use a concave parabolic primary mirror to collect and focus
incoming light into a flat secondary mirror, which reflects the image into the eyepiece.
Primary mirror
- gathers incoming light and forms a sharply focused image of the object being viewed.
Secondary mirror -
reflects light from the primary mirror to the eyepiece. It’s also know as a diagonal mirror
because it is at 45
°
with respect to the optical axis.
“Seeing” or “seeing conditions”
- refer to the stability of the atmosphere, transparency and sky illumination.
See the section of the manual entitled "Seeing Conditions".
Thermal turbulence -
turbulence caused by temperature variations. Some sources of turbulence are
differences in temperature between the telescope tube and the air within it, or viewing near a heat source,
such as a roof top or parking lot releasing stored daytime heat.
