Paramount User Guide
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P a g e
negative altitude are below the horizon. For example, the Sun just after sunrise is close to the horizon so
it has an altitude of a couple of degrees, and just after sunset its altitude is minus one or two degrees.
Azimuth
The azimuth (az) of an object is generally reckoned from North, increasing in the clockwise direction, and
ranges from 0 to 359 degrees. North is 0 degrees, east is 90 degrees, south is 180 degrees and west is 270
degrees.
When the Paramount is controlled by
TheSkyX Professional Edition
, attempting to slew the mount below
the local horizon is not permitted and will result in an error message.
The Equatorial Coordinate System
The horizon coordinate system is not convenient for specifying the location of celestial objects because
the horizon coordinates of stars and other objects are continuously changing with time (due to the
rotation of the Earth).
The exception occurs with objects near the north and south celestial poles. These positions are unique
since they are near to the axis of rotation of the Earth and therefore move only in small circular paths.
Polaris, the North Star, for example, remains at a nearly constant altitude and azimuth. In the equatorial
coordinate system, the coordinates of all celestial objects remain fixed* from hour-to-hour, day-to-day
and so on.
An object's equatorial coordinates remain the same regardless of from where on Earth the object is
viewed. This allows astronomers to create star maps that apply to any place on Earth, or publish the
anticipated position of an upcoming comet so that astronomers everywhere know where it is located
among the stars.
The equatorial coordinate system used to specify the positions of celestial objects is directly analogous to
the latitude-longitude coordinate system used on Earth. In fact, if you were to expand the latitude and
longitude grid of the Earth so that it is out beyond all stars, you would have a sphere with identical
geometry to the celestial sphere.
We suppose that all stars and deep-sky objects are located on a very large sphere (out beyond all stars).
We call this the celestial sphere. For purposes of describing the positions of celestial objects, we consider
all stars and deep sky objects to be on the celestial sphere, when actually they are all positioned at varying
distances from the Earth.
* Equatorial coordinates change over long periods of time due to precession (wobbling of the Earth).
TheSkyX computes this change in stars’ position for the current date. Precession, however, does not
change the relative positions of objects with respect to one another.
