# Square degree

A **square degree** (**deg ^{2}**) is a non-SI unit measure of solid angle. Other denotations include

*sq. deg.*and (°)

^{2}. Just as degrees are used to measure parts of a circle, square degrees are used to measure parts of a sphere. Analogous to one degree being equal to π/180 radians, a square degree is equal to (π/180)

^{2}steradians (sr), or about 1/3283 sr = 3.0462×10

^{−4}sr (0.30462 msr).

Square degree | |
---|---|

Unit of | Solid angle |

Symbol | deg^{2} |

Conversions | |

1 deg^{2} in ... | ... is equal to ... |

SI units | 3.04617×10^{−4} sr |

The whole sphere has a solid angle of 4πsr which is approximately 41253 deg^{2}:

## ExamplesEdit

- The full moon covers only about 0.2 deg
^{2}of the sky when viewed from the surface of the Earth. The Moon is only a half degree across (i.e. a circular diameter of roughly 0.5 deg), so the moon's disk covers a circular area of: π × (0.5°/2)^{2}, or 0.2 square degrees. The moon varies from 0.188 to 0.244 deg^{2}depending on its distance to the Earth. - Viewed from Earth, the Sun is roughly half a degree across (the same as the full moon) and covers only 0.2 deg
^{2}as well. - It would take 210100 times the full moon (or the Sun) to cover the entire celestial sphere.
- Conversely, an average full moon (or the Sun) covers a
/ 210100 fraction, or less than 1/1000**2**^{th}of 1 percent (0.00000952381) of the celestialsphere, or above-ground "sky".**hemi** - Assuming the Earth to be a sphere with a surface area of 510 million km
^{2}, the area of Northern Ireland (14130 km^{2}) and Connecticut (14357 km^{2}) represent a solid angle of 1.14 deg^{2}and 1.16 deg^{2}, respectively. - The largest constellation, Hydra, covers a solid angle of 1303 deg
^{2}, whereas the smallest, Crux, covers only 68 deg^{2}.^{[1]}