Unit Conversion
A common problem in astronomy is the conversion of a quantity measured in some
units into a quantity based on other units.
There are also several `systems of measurement' in use in physics and astronomy.
The common systems are mks,
for meter-kilogram-second, cgs,
for centimeter-gram-second, and SI or
the System Internationale (SI). SI is essentially an expanded mks system that
includes a large variety of other standard units for quantities such as energy,
force and magnetic flux.
Here is a list of useful conversions:
Length:
- 1inch = 2.54 cm
- 1 mile = 1.6 km
- 1 km = 1000 m
- 1 m = 100 cm = 1000 mm = 109 nm
- 1 Angstrom = 10-10 m
= 10-8 cm
- 1 AU = 1.4960×1011 m
= 1.4960×108 km
(Astronomical Unit)
- 1 AU = 149,597,870,700 m (According to the 2015
International Astronomical Union General Assembly in Honolulu)
- 1 ly = 9.4605×1015 m
= 9.4605×1012 km
(light year)
- 1 pc = 3.0857×1016 m
= 3.0857×1013 km
= 3.2616 ly = 206265 AU (parsec)
- 1 Mpc = 106 pc =
3.2616×106 ly
(Megaparsec)
Angles:
- 1° =
1 degree = 60' = 60 arcminutes
- 1' = 60" = 60 arcseconds
- 1 radian = 360° /2p =
57.3° =
206265"
Mass:
- 1 kg = 2.20462 lb
- 1 Solar Mass = 1.9891×1033 gram
= 1.9891×1030 kg
Time:
- Sidereal Day = 23h 56m 04.09054s
- Solar Day = 24h =
86400 s
- Sidereal Year = 3.155815×107 s
- Tropical Year = 3.155693×107 s
Energy:
- 1 Joule = 2.39×10-1 calorie
- 1 Joule = 107 ergs
- 1 Solar Luminosity = 3.826×1033 ergs/s
= 3.826×1026 Joules/s
= 3.826×1026 Watts
- 1 Solar Luminosity = 3.828×1033 ergs/s
= 3.828×1026 Joules/s
= 3.828×1026 Watts
(According to the 2015 International Astronomical Union General Assembly in
Honolulu)
- 1 Jansky = 10-26 Joules
s-1 m-2 =
10-26 Watts m-2
Link:
https://www.cfa.harvard.edu/~dfabricant/huchra/ay145/units.html