Everything about Spherical Astronomy totally explained
Spherical astronomy or
positional astronomy is the branch of
astronomy that's used to determine the location of objects on the
celestial sphere, as seen at a particular date, time, and location on the
Earth. This is one of the oldest branches of astronomy. It relies on the mathematical methods of
spherical geometry and the measurements of
astrometry.
This is the oldest branch of astronomy and dates back to
antiquity. Observations of celestial objects have and continue to be, important for religious and
astrological purposes, as well as for
timekeeping and
navigation. The science of actually measuring positions of celestial objects in the sky is known as
astrometry.
The primary elements of spherical astronomy are coordinate systems and time. The coordinates of objects on the sky are listed using the
equatorial coordinate system, which are based on the projection of the
Earth's
equator onto the celestial sphere. The position of an object in this system is given in terms of
right ascension (α) and
declination (δ). The latitude and local time can then be used to derive the position of the object in the
horizontal coordinate system, consisting of the
altitude and
azimuth.
The coordinates of celestial objects such as stars and galaxies are tabulated in a
star catalog, which gives the position for a particular year. However the combined effects of
precession and
nutation will cause the coordinates to change slightly over time. The effect of these changes in the movement of the Earth are compensated by the periodic publication of revised catalogs.
To determine the position of the
Sun and planets, an astronomical
ephemeris is used. This gives the positions of these objects on the celestial sphere at a particular date and time, which can then be converted into suitable coordinates.
The unaided human eye can detect about 6000
stars, of which about half are below the horizon at any one time. On modern star charts, the
celestial sphere is divided into 88
constellations. Every star lies within a constellation.
Constellations are useful for
navigation.
Polaris lies close to due north to an observer in the northern hemisphere. This star is always at a position nearly over the
north pole.
Positional phenomena
Ancient structures associated with positional astronomy include
Arkaim
Chichen Itza
The Medicine Wheel
The Pyramids
Stonehenge
The Temple of the SunFurther Information
Get more info on 'Spherical Astronomy'.
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