Definition:Declination

Definition

Consider the celestial sphere $C$ with observer $O$.

Let $P$ and $Q$ be the north celestial pole and south celestial pole respectively.

Let $X$ be a point on $C$.

Let $PXQ$ be the vertical circle through $X$.

Let $D$ be the point where the celestial equator intersects $PXQ$.

The length of the arc $DX$ of $PXQ$ is known as the declination of $X$.

North Declination

If $X$ is in the northern celestial hemisphere, $DX$ is north declination.

South Declination

If $X$ is in the southern celestial hemisphere, $DX$ is south declination.

It is convenient to define the declination of $X$ as between $+90 \degrees$ and $-90 \degrees$, where a south declination is a negative quantity, from $0$ at the celestial equator and $-90 \degrees$ at the south celestial pole.

Also known as

Declination can also be seen as its abbreviation dec.

Symbol

The symbol used to denote declination is $\delta$.

Also see

• Definition:Codeclination

• Results about declination can be found here.

Sources

• 1976: W.M. Smart: Textbook on Spherical Astronomy (6th ed.) ... (previous) ... (next): Chapter $\text {II}$. The Celestial Sphere: $19$. Declination and hour angle.
• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): declination (dec)
• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): equatorial coordinate system
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): declination (dec)
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): equatorial coordinate system