Celestron Ultima 8 Instruction Manual page 110

Field Rotation
Focal Ratio, f#
Go To
Hex
Latitude
Longitude
Meridian
Messier
North Celestial Pole
Objective
Parallax
Parfocal
Polar Alignment
Prime Focus
110
This is when the star images in a field of view of some device rotate about the center of the
field. This occurs when you have a telescope that is tracking the sky and is not polar aligned.
At the celestial equator, this effect is minimized. At the celestial poles this effect is
maximized. The Ultima 2000 will exhibit field rotation when you are using it in the Alt-Az
configuration.
The ratio of the focal length to aperture.
This a feature that is unique to a computerized telescope. When the telescope is given the GO
TO command, it slews to the current object selected in its object catalog.
Short for hexadecimal. This is a base-16 numbering system. Rather than having 10 different
integers, like the decimal system, hexadecimal has 16 different integers. They are; 0-9, A, B,
C, D, E, F. A=10, B=11, ... , and F=15.
The coordinate system on the Earth which measures angular distance from the equator. The
equator is 0º and the North pole is 90º. When polar aligning a telescope, the altitude the
Celestial pole is above the horizon is equal to the latitude of the observing sight.
The coordinate system on the Earth which measures the angular distance around the planet
orthogonal to its axis of rotation.
A reference line in the sky that starts at the North celestial pole and ends at the South celestial
pole and passes through the zenith. If you are facing South, the meridian starts from your
Southern horizon and passes directly overhead to the North celestial pole.
Messier was a French astronomer in the late 1700's who was primarily looking for comets.
Comets are hazy diffuse objects and so Messier cataloged objects that were not comets to help
his search. This catalog became the Messier Catalog, M1 through M110.
The point in the Northern hemisphere around which all the stars appear to rotate. This is
caused by the fact that the Earth is rotating on an axis that passes through the North and South
celestial poles.
Refers to the primary mirror of a reflecting telescope or the front lens of a refracting telescope.
The difference in apparent direction of an object as seen from two different points. Humans
can distinguish distances between objects due to the parallax caused by having two eyes. Most
astronomical objects are so for away that the effects of parallax are negligible.
Refers to a group of eyepieces that all require the same distance from the focal plane of the
telescope to be in focus. This means when you focus one parfocal eyepiece all the other
parfocal eyepieces, in a particular line of eyepieces, will be in focus.
Making the axis of rotation of a telescope mount parallel to the axis of rotation of the Earth.
This usually refers to the position of an instrument, like a camera, on a telescope. A telescopes
objective focuses on a plane known as the focal plane. Placing a camera in a position such that
the film plane coincides with the focal plane is known as placing the camera at prime focus.
Glossary