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Astronomical Unit
-----------------
1 au is roughly the distance from the Earth to the
Sun. However, the distance varies as Earth orbits the
Sun. The distance changes from a maximum (aphelion)
to a minimum (perihelion) and back again once a year.
It was originally defined as the average of the aphelion
and perihelion, but is now defined as exactly
149,597,870,700 metres (93 million miles).
Parsec
------
A parsec is a unit of length used to measure large
distances to objects outside the Solar System. One
parsec is the distance at which one astronomical
unit subtends an angle of one arcsecond. A parsec
is equal to about 3.26 light-years.
Minute = 1/60 degrees
Arc minute 1/(60*360) = 1/21,600 degrees
Arc second 1/(60*360*60) = 1/1,296,000 degrees
+ ^
/| |
/θ| |
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E . S . v
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<- 1au ->