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

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}:

- 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°), 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 from 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 2 / 210100 fraction, or less than 1/1000 of a percent (0.00000952381) of the celestial hemisphere, or above-the-horizon sky.
- Assuming the Earth to be a sphere with a surface area of 510 million km
^{2}, the area of Northern Ireland (14130 km^{2}) represents a solid angle of 1.14 deg^{2}, Connecticut (14357 km^{2}) represents a solid angle of 1.16 deg^{2}, Equatorial Guinea (28050 km^{2}) represents a solid angle of 2 deg^{2}. - The largest constellation, Hydra, covers a solid angle of 1303 deg
^{2}, whereas the smallest, Crux, covers only 68 deg^{2}.^{[1]}

**^**"RASC Calgary Centre - The Constellations".*calgary.rasc.ca*. Retrieved 2022-02-16.

- "Square Degrees - the Area of something on the sky". The RASC Calgary Centre. 2018-11-05. Retrieved 2022-01-21.