In Indian Astronomy, Chara is the Ascensional Difference and is the difference between Right Ascension and Oblique Ascension.
And is calculated by the equation
Sin ( Chara ) = tan ( decl ) tan ( latitude ).
Here Theta is Chara.
Sin C is called Chara Jya
Right Ascension means the longitudes measured along the Celestial Equator, the Vishu vat Vritta.
Oblique Ascension means the longitudes measured along the Ecliptic, the Kranti Vritta.
Chara is used in the computation of Sunrise and Sunset.
The formula for Sunrise = 6 H + Equation of Time – Chara – Refraction Correction
The formula for Sunset = 18 H + Equation of Time + Chara + Refraction Correction.