Glossary
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Resolution
The minimum detectable angle an optical system can detect. Because of diffraction, there is a
limit to the minimum angle, resolution. The larger the aperture, the better the resolution as
shown by the equation,
θ
λ
=
•
1 22
.
D
where
θ
is the resolution of the system, in radians,
λ
is the wavelength of light, and D is the
diameter of the objective lens.
Right-Ascension (RA)
This is like the terrestrial longitude system extended onto the sky. The difference is this
coordinate system is fixed to the sky rather than being fixed to the Earth. Therefore, the RA of
a point in the sky does not change. Used in conjunction with Declination, an objects position
can be defined.
Sidereal Rate
This is the angular speed at which the Earth is rotating. Telescope tracking motors drive the
telescope at this rate. The rate is 15 arc seconds per second or 15 degrees per hour.
Slew
When the telescope moves quickly across the sky, this is referred to as slewing. But, some
refer to slewing as any time the telescope is moving at greater or less than sidereal rate such
that an object in the eyepiece can noticeable be seen to move rapidly. For a telescope tracking
at sidereal rate, an object in the eyepiece does not move at all.
South Celestial Pole
The point in the Southern 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.
User Interface
The display screen and the control buttons on the hand control that allow the telescope to be
used and commanded.
Warp
When the Ultima 2000 is aligned to the sky a warp error is given. The number is measured in
degrees and it tells you how well the angle between the alignment objects matches the angle the
telescope measured itself move.
Wedge
A wedge allows the telescope to be polar aligned. The wedge is attached to the tripod and the
telescope is attached to the wedge. The wedge has a tilt plate that the telescope is attached to
which allows the angle of the R.A. axis of the telescope to be adjusted to match the angle of the
Earth’s axis of rotation.
Zenith
The point directly over head or 90º altitude.
