Celestial latitude & Celestial longitude

Celestial Coordinate System 

It is commonly used for locating the positions and orbits of  Solar System objects. Because most planets (except Mercury), and many small heavenly bodies have orbits with small inclinations to the ecliptic, it is convenient to use it as the fundamental plane.

THE CELESTIAL SPHERE

The celestial sphere is a large imaginary sphere of infinitely large radius surrounding the universe such as all the celestial bodies appears to be projected on to its surface .The Earth lies at the center of this imaginary sphere. The Sun, Moon, and other Planets, stars, and nebulae appears to be located on the sphere like a band around the Earth.

The sphere appears to be rotating from East to West every twenty-four hours, so celestial bodies appear to rise in the east and set in the west. (The earth's rotation creates the illusion that the celestial sphere is rotating.) and with it we can keep references to where celestial bodies lie in the sky.

The daily eastward rotation of Earth on its axis produces an apparent diurnal westward rotation of the starry sphere. Thus, the stars seem to rotate about a northern or southern celestial pole, the projection into space of Earth’s own poles. Equidistant from the two poles is the celestial equator; this great circle is the projection into space of Earth’s Equator.

An astronomer can only see half the sky at a time, that is, only half the sky is above the horizon at any time. But the sky keeps moving as the earth rotates. Just as the sun rises and sets every day, so does every star in the sky each night. The celestial sphere is a large sphere surrounding the earth and with it we can keep references to where celestial bodies lie in the sky.

• North Celestial Pole (NCP) and the South Celestial Pole (SCP) -

The fundamental plane divides the celestial sphere into two equal hemispheres called northern hemisphere and southern hemisphere. and this divide marks the baseline for latitudinal coordinates, similar to the equator in the geographic coordinate system.

The Celestial Sphere "rotates" on the Celestial Axis, which goes through earth’s north and south poles and extends out to the Celestial Sphere intersecting it at the North Celestial Pole (NCP) and the south Celestial Pole (SCP).

• Celestial Equator - The earth's equator, but at a much greater radius. If the earth's equator was a rubber band, then the celestial equator is the same rubber band just stretched away from the earth.
The Celestial Equator is an imaginary line around the middle of the Celestial Sphere, equidistant from the NCP and SCP and on the same plane as the earth's equator. It intersects the Circle of the Horizon at East and due West.

In the ecliptic system of astronomical coordinates, celestial longitude is measured in degrees east from the vernal equinox along the ecliptic.

Celestial latitude

The angular distance north, counted positive, or south, counted negative, measured from the ecliptic along a great circle drawn through the pole of the ecliptic plane and a celestial body. Also called ecliptic latitude.
Celestial latitude is measured in degrees north (positive) or south (negative) from the ecliptic to the ecliptic poles. Each ecliptic pole is 23.44° from the corresponding celestial pole.

Horizon - The Circle of the Horizon surrounds the earth-bound observer, who is standing in the middle of it. Points on the horizon are called directions. The horizon circle is divided into 360°s, with 90°s between each of the four cardinal directions of North, South, East, and West.

The horizon changes depending on your position on earth.

Zenith- The point on the celestial sphere directly overhead.

 Meridian- The line that extends from the north point on the horizon upwards through the zenith and then downward to the south point on the horizon.

Or we can say  The Meridian is an imaginary circle passing through the Zenith and NCP and SCP and is always perpendicular to the horizon.

Position of Stars on the Celestial Sphere - Celestial Coordinates: 

Stars appear fixed on the Celestial Sphere as it rotates. Their coordinates are given in two numbers, Declination and Right Ascension, which represent imaginary lines, like latitude and longitude on the earth’s surface. The intersection of the Declination and Right Ascension lines gives a point that represents the position of a body on the Celestial Sphere.

Declination is the angle of a heavenly body away from the Celestial Equator with the vertex (the common endpoint of the angle) being the center of the earth). Analogous to the latitude on Earth, the Declination of an object on the celestial sphere is measured northward or southward from the plane containing the equator.

The declination of the equator is 0 degrees, the North Celestial Pole, +90 degrees, the South Celestial Pole, -90 degrees.

A celestial body on the Celestial Equator has a declination of 0 and rises due East and sets due West. (The sun at Vernal and Autumnal Equinox has a declination of 0.)
Celestial bodies to the north of the Celestial Equator have positive declination of up to +90°s, which is the declination of the NCP.

Celestial bodies south of Celestial Equator have negative declination of up to –90°s, which is the declination of the SCP. With the observer at the equator, a star with a declination of – 45°s would rise in the SE and set in the SW.

Right Ascension

Analogous to the longitude on Earth, the Right Ascension of an object on the celestial sphere is measured along the celestial equator, as the angular distance to some fiducial direction for with R.A. = 0 degrees. By convention, this fiducial direction is the point on the celestial where the Sun is found on the first day of spring (the vernal equinox).

Right Ascension [RA], gives the position of a heavenly body in relationship to lines from the NCP to the SCP, intersecting the Celestial Equator halfway in between at right angles. (These lines are like longitude lines, which run between the North and South Poles on Earth and intersect the Earth’s Equator perpendicularly.)

The zero point for RA on the Celestial Equator is the position of the sun at vernal equinox, called the vernal point. RA is given in hours (H) and minutes (M), with 0 and 24H equal to the same point. 24 hours is used because the earth is rotating, once every 24 hours, which equals one revolution of the Earth / Celestial Sphere / Celestial Equator.

One hour = 15°s. 

So a star at the horizon rising in the East will take one hour to rotate up on the Celestial Sphere 15°s above the Eastern Horizon; 24 hours later it will be back rising in the East. A star 15°s above the Western horizon on the Celestial Equator will take one hour to reach the Western horizon and set.

At the vernal point, the sun is near the constellation of Pisces on the Celestial Sphere. Stars in this constellation have a RA near 0.

Stars and galaxies have (almost) fixed positions in Right Ascension and Declination. The Sun and planets, on the other hand, move among the distant stars so that their coordinates change throughout the year. Because of the Earth's yearly orbital motion, the Sun appears to circle the ecliptic

#Celestial_Latitude, #Celestial_Longitude, #Declination, #Right_Ascension, #Celestial_Coordinates, #Celestial_Sphere, #Astronomy_Relevant_To_Astrology, #Vedic_Astronomy