Glossary
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GLOSSARY
16-bit This is the resolution of the software of the Ultima 2000. 16-bit resolution gives 2
16
discrete
integers for the software to calculate the transformation from RA/DEC to Alt-Az.
Airy Disk The central bright spot in the focused diffraction pattern of an optical system. A star focused
in a telescope forms a diffraction pattern rather than a point. The diffraction pattern looks like
a central bright spot with a series of rings around it which are successively less bright. If the
telescope is defocused a slight amount, the diffraction pattern is easier to see. The diffraction
pattern is small, so in order to see it, you must use a high power eyepiece. Furthermore, the
radius of the Airy Disk is inversely dependent on the radius of the aperture of the telescope.
The larger the telescope, the smaller the Airy Disk, therefore the better the resolution.
Alignment Stars These are stars used to align the Ultima 2000’s model of the sky with the actual sky. The
Ultima 2000 has a list of 28 bright alignment stars. You do not have to align the telescope to
only these stars as any object contained in the database of the Ultima 2000 can be used.
All-Sky Pointing
Accuracy
This refers to how well the telescope points at objects all over the sky. It is common for
computerized telescopes to point well near their alignment stars but not quite as well away
from their alignment stars.
Altazimuth A form of telescope mounting in which the two independent rotation axes allow movement of
the instrument in altitude (up/down) and azimuth (left/right). It is the simplest type of
telescope mounting but it requires movement of both axes in order to track the motion of the
stars. For that reason it was not a suitable mount for amateur telescopes until computerized
telescopes, like the Ultima 2000, were made available.
Altitude The angle between the horizon and a point in the sky. Directly overhead is 90º and the horizon
is 0º. Usually used in conjunction with azimuth to locate a specific point in the sky from a
specific location.
Aperture The diameter of the objective lens.
Astronerd A person that all should aspire to be like.
Auto guider A CCD chip used in place of a guiding eyepiece for long exposure astrophotography or CCD
imaging. The auto guider makes fine adjustments to the telescopes tracking rate to correct for
errors in the tracking gears. It can also make adjustments in declination to correct for polar
alignment errors.
Azimuth The angle between the direction of a point with North. Usually used in conjunction with
altitude to locate a specific point in the sky from a specific location. It is standard that azimuth
is measured by the number of degrees a point is away from North. South would be 180º. A
compass measures azimuth.
Back Focus Refers to how far back of the rear cell (back of the telescope) the telescope focuses. This only
applies to telescopes with a variable focus like a Schmidt-Cassegrain.
Backlash
Compensation
This minimizes the effect of backlash (see Backlash Dead Zone) by running the motors at
maximum speed through the dead zone then returning to the normal speed just as the dead zone
is traversed. The Ultima 2000 does this automatically and allows you to change the
compensation value.
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