Glossary
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Backlash Dead Zone
Gears in telescope have some amount of play. The dead zone refers to the time it takes for the
gears to traverse the play. This is seen in the eyepiece as a period when the telescope does not
move even though the motors have been activated. It is most noticeable when the direction of
the motor is changed.
CCD
Abbreviation for charge-coupled device. An electronic imaging device widely used in
astronomical applications. The CCD consists of semiconducting silicon; when photons of light
fall on it, free electrons are released. An array of electrodes collect the liberated electrons in
the same pattern as the photons fall onto the silicon. Each electrode is known as a well or a
pixel. Electric charge in each pixel is transferred through a series of gates to a place where the
charge can be counted and converted into a form in which the whole image can be stored in a
computer.
Clutch
An adjustable mechanism that causes friction between the drive gears of the telescope and the
telescope itself. The advantage to a clutch drive system is that the telescope can be moved by
hand or by the motors.
Collimation
The alignment of the optical components of an optical system. In Schmidt-Cassegrains, the
secondary mirror is adjusted in order to collimate the system. In Newtonian telescopes the
primary mirror is adjusted.
Control Buttons
Refers to the UP, DOWN, and ENTER buttons on the hand control of the Ultima 2000. These
buttons control the software.
Declination (DEC)
This is the terrestrial latitude system projected onto the sky. Used with Right Ascension, an
objects location can be defined. The system of RA and DEC is referred to as the Celestial
Coordinate System.
Diamond Buttons
Refers to the four directional buttons on the hand control of the Ultima 2000 that control the
motors. These buttons are laid out in a diamond pattern and are diamond shaped.
Diffraction
Since light behaves like a wave when it encounters an edge, or in our case, an aperture, a
focused plane wave does not form a point. It forms a pattern with a central bright disk with
successively dimmer rings. Each are separated by dark rings. See Airy Disk
Downstop
A reference position for the optical encoders on the Ultima 2000. There is an encoder for each
axis, Altitude and Azimuth. Each of these axes has a downstop. The Altitude downstop is a
black pin located on the inside of the fork arm which contacts a black pin located on the front
cell of the tube. The Azimuth downstop position is referenced by a sticker located on the drive
base and a sticker located on the polar housing. Line up the two stickers for the downstop
position.
Point Source
An object which cannot be resolved into an image because it to too far away or too small is
considered a point source. A planet is far away but it can be resolved as a disk. Most stars
cannot be resolved as disks, they are too far away. The image of a point source is a diffraction
pattern formed by the aperture interacting with the plane wave (light from a distant object).
Extended Object
An object that has some measurable angle. Some examples are the Moon, Jupiter, the
Andromeda Galaxy, and the Dumbbell Nebula. The significance of an extended object versus
a point source in astronomy is that the extended object has a surface brightness.
