Meade Instruments LX200 - Manual (Page 70)

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Telescopes · Binoculars · Microscopes
Meade LX200 Instruction Manuals
7" Maksutov-Cassegrain Telescope 8", 10", and 12" Schmidt-Cassegrain Telescopes
APPENDIX B: EQUATORIAL USE
IMPORTANT NOTICE! Never
use a telescope or spotting
scope to look at the Sun!
Observing the Sun, even for
the shortest fraction of a
second, will cause irreversible damage
to your eye as well as physical damage
to the telescope or spotting scope itself.
[ toc ] 1. Celestial Coordinates: Declination and Right Ascension
Analogous to the Earth-based coordinate system of latitude and
longitude, celestial objects are mapped according to a coordinate
system on the "celestial sphere," the imaginary sphere on which all
stars appear to be placed. The Poles of the celestial coordinate
system are defined as those 2 points where the Earth's rotational
axis, if extended to infinity, North and South, intersect the celestial
sphere. Thus, the North Celestial Pole is that point in the sky where an extension of the Earth's axis
through the North Pole intersects the celestial sphere. In fact, this point in the sky is located near the North
Star, or Polaris.
On the surface of the Earth, "lines of longitude" are drawn between the North and South Poles. Similarly,
"lines of latitude" are drawn in an East-West direction, parallel to the Earth's equator. The celestial equator
is simply a projection of the Earth's equator onto the celestial sphere. Just as on the surface of the Earth,
imaginary lines have been drawn on the celestial sphere to form a coordinate grid. Celestial object
positions on the Earth's surface are specified by their latitude and longitude.
The celestial equivalent to Earth latitude is called "Declination," or simply "Dec," and is measured in
degrees, minutes or seconds north ("+") or south ("-") of the celestial equator. Thus any point on the
celestial equator (which passes, for example, through the constellations Orion, Virgo and Aquarius) is
specified as having 0°0'0" Declination. The Declination of the star Polaris, located very near the North
Celestial Pole, is +89.2°.
The celestial equivalent to Earth longitude is called "Right Ascension," or "R.A." and is measured in hours,
minutes and seconds from an arbitrarily defined "zero" line of R.A. passing through the constellation
Pegasus. Right Ascension coordinates range from 0hr0min0sec up to (but not including) 24hr0min0sec.
Thus there are 24 primary lines of R.A., located at 15 degree intervals along the celestial equator. Objects
located further and further east of the prime (0h0m0s) Right Ascension grid line carry increasing R.A.
coordinates.
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