A square degree is a non-SI unit measure of solid angle. It is denoted in various ways, including deg2, 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 or about 1/3283 steradian. The number of square degrees in a whole sphere is
or approximately 41 253 deg2. This is the total area of the 88 constellations in the list of constellations by area.
For example, observed from the surface of the Earth, the Moon has a diameter of approximately 0.5°, so it covers a solid angle of approximately 0.196 deg2, which is 4.8 × 10−6 of the total sky sphere.
Famous quotes containing the words square and/or degree:
“This house was designed and constructed with the freedom of stroke of a forester’s axe, without other compass and square than Nature uses.”
—Henry David Thoreau (1817–1862)
“Take but degree away, untune that string,
And hark what discord follows!
...
Force should be right, or, rather, right and wrong—
Between whose endless jar justice resides—
Should lose their names, and so should justice too.
Then everything includes itself in power,
Power into will, will into appetite;
And appetite, an universal wolf,
So doubly seconded with will and power,
Must make perforce an universal prey,
And last eat up himself.”
—William Shakespeare (1564–1616)