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A.1 Angular Quantities

In astronomy, angular quantities are generally expressed in sexagesimal units. The main units of measure of plane and solid angles are the following:

$\displaystyle 1~\textrm{degree}=1~\textrm{deg}$

$\displaystyle 1~\textrm{second~of~arc}=1~\textrm{arcsec}=1~\textrm{as}=\frac{1}{3600}~\textrm{deg}=10^3~\textrm{mas}=10^6~\mu\textrm{as}$

$\displaystyle 1~\textrm{radian}=1~\textrm{rad}=\frac{180}{\pi}~\textrm{deg}=\frac{648000}{\pi}~\textrm{arcsec}$

$\displaystyle 1~\textrm{square~degree}=1~\textrm{deg}^2$

$\displaystyle 1~\textrm{steradian}=1~\textrm{sterad}=\frac{32400}{\pi^2}~\textrm{deg}^2$

The whole sky spans a solid angle

$\displaystyle \Omega_{sky}=4\,\pi~\textrm{sterad}=\frac{129600}{\pi}~\textrm{deg}^2~,$

while the sky region where the absolute value of the Galactic latitude $ b$ is greater than a given value $ \phi$ measures

$\displaystyle \Omega\left(\vert b\vert>\phi\right)=4\,\pi\,\sin\phi~~~\textrm{[sterad]}~.$


next up previous contents
Next: A.2 Photometric Quantities Up: A. Units of Measure, Previous: A. Units of Measure,   Contents
Mattia Vaccari 2000-12-05