Astronomical measurement of Celestial Earth

A)    Celestial Sphere / Cosmic Sphere: The imaginary sphere in the space surrounding our entire Solar system.

B)    Celestial Poles: If the Earth axis is extended infinitely towards North and South, it will meet the imaginary surface of the cosmic sphere at some point.

These points on the surface of cosmic sphere are known as the Celestial Poles and the extended axis becomes the imaginary axis of the celestial sphere.

C)     Celestial Equator: The projection of earth’s equator on the imaginary surface of the celestial sphere is called ‘Celestial Equator’.

As the Earth’s equator divides the globe into two halves, similarly the celestial equator divides cosmic sphere into two equal halves. These are known as Northern Celestial Hemisphere and Southern Celestial Hemisphere.

D)    Ecliptic (Ravi Marg):  The apparent path of the Sun in the space along which it seems to move around the earth is known as ‘Ecliptic’. The Ecliptic (or) the Ravi Marg like the orbits of other planets is not a circle but is elliptical or oval in shape.  Thus, Ecliptic can also be defined as a projection of earth’s orbit around the sun on to the surface of cosmic sphere.

The plane of ecliptic is inclined to the plane of celestial equator at an angle of about 23 1/2˚ due to the slant/inclination of the earth’s axis to the vertical.

E)     Zodiac [Bhranti Chakra]:  If one observes the movement of planets, it is seen that they also move in their own orbits along with the Sun’s path, their path deflects north-south also.

However the planets never precede more than 9˚ either north or south of the ecliptic. Hence if a parallel line on either side of the ecliptic is drawn at an angular distance of about 9˚, then the ecliptic will come in the middle and either side will be a broad band way in which all planets can be located.

F)     Celestial Longitude (Sphuta): This is the arc of the ecliptic intercepted between the first point of Aries and a perpendicular arc to the ecliptic drawn through the body (planet) and the poles of the ecliptic.

In other words, it can also be defined as the angular distance of any heavenly bodies (Planets, etc) measured in degrees along the ecliptic, in one direction from the origin for the reference point – first point of Aries of the zodiacal sign or the Vernal equinox.

The first point of Aries is different in Sayana and Nirayana system.

G)    Celestial Latitude (Vikshepa): It is the angular distance across the celestial sphere measured north or south from the ecliptic along the great circle passing through the poles of the ecliptic and the object.

H)    Declination (Kranti): It is the angular distance on the celestial sphere north or south of the celestial equator. It is measured along the hour circle passing through the celestial object.

I)       Right Ascension (Dhruva): It is the angular distance on the celestial sphere measured eastward along the celestial equator from the vernal equinox to the hour circle passing through the celestial object.

J)       Oblique Ascension (Rashimaan): Rashimaan means the rising periods of each of the 12 rashis or signs of the zodiac. It is the time required/taken by each Sign to rise completely through its 30 degrees on the eastern horizon of any place on Earth.

AE = Autumnal Equinox;  

VE = Vernal Equinox;  

SS = Summer Solstice;

WS = Winter Solstice;  

WOE = Celestial Equator; 

W’OE’ = Ecliptic;

NPP2S = One side of Great Circle (Circle of Declination) passing through the planet P, and Poles N & S, perpendicular to the Celestial Equator  and intersecting at a point P2.

N’PP1S’ = One side of the Great Circle passing through Planet (P) and Poles N’-S’ of the Ecliptic and perpendicular to it (Ecliptic) and intersecting the Ecliptic at P1.

OP1 = Angular distance measured along the Ecliptic (or) we can call this as Celestial Longitude of Planet P.

PP1 = Angular distance measured perpendicular to Ecliptic. It is Celestial Latitude of Planet P. As ‘P’ is situated above the Ecliptic in the Northern hemisphere, the celestial latitude will be north.

OP2 = Angular distance measured along the celestial equator. It is therefore right ascension of Planet P.

PP2 = Angular distance measured perpendicular to celestial equator. So, it is declination of Planet P. As the planet P is situated in Northern hemisphere, the declination of the planet will be north.