Appendix: Constants and Units
Appendix: Constants and Units
In addition to the meter (m), kilogram (kg), and second (s), there are several units commonly used in astronomy. We list these and provide some conversions, astronomical constants, and the metric prefix converter.
| Astronomical Units | ||
| Name | Symbol | Value |
| astronomical unit | AU | 149.6 x 106 km = 93 million miles |
| light-year | ly | 9.46 x 1012 km = 6 trillion miles |
| parsec | pc | 3.26 ly = 206,265 AU |
| Ångstrom | Å | 10-10 meters |
| micron | μ | 1 micrometer = 10-6 meters |
| Kelvin | K | oC+273 |
| Astronomical Constants and Measurements | ||
| Name | Symbol | Value |
| speed of light | c | 3 x 108 meters/sec |
| mass of the Sun | Msun | 1.989 x 1030 kilograms |
| radius of the Sun | Rsun | 6.96 x 108 m = 432, 494 miles |
| luminosity of the Sun | Lsun | 3.83 x 1026 J/sec |
| mass of Earth | MEarth | 5.98 x 1024 kg |
| mass of Jupiter | MJ | 317.03 MEarth |
| radius of Earth (equatorial) | REarth | 6378.2 km = 3963.4 miles |
Metric Prefixes
These prefixes are used before fundamental units like meter, Hertz, or second. Factors with positive exponents increase the number of zeros after the number. For example, a kilometer, km, is 1,000 meters; a gigaHertz, GHz, is 1 billion Hertz or 1,000,000,000 Hertz. Prefixes with negative factors are less than unity. A nanometer (nm) is a billionth of a meter or 0.000 000 001 meter; a millisecond (ms) is a thousandth of a second or 0.001 second.
| Metric System Prefixes | ||
| Name | Symbol | Factor |
| yotta | Y | 1024 |
| zetta | Z | 1021 |
| exa | E | 1018 |
| peta | P | 1015 |
| tera | T | 1012 |
| giga | G | 109 |
|---|---|---|
| mega | M | 106 |
| kilo | k | 103 |
| hecto | h | 102 |
| deka | da | 10 |
| deci | d | 10-1 |
| centi | c | 10-2 |
| milli | m | 10-3 |
| micro | μ | 10-6 |
| nano | n | 10-9 |
| pico | p | 10-12 |
| femto | f | 10-15 |
| atto | a | 10-18 |
| zepto | z | 10-21 |
| yocto | y | 10-24 |
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott