As more scientific analyses and observations are interlinked via the web it becomes more important to adopt standardized units so that information can be easily compared and used outside of specialized fields. In minimize potential confusion, the AAS machine readable (MR) tables use standard SI units in most cases. For example, the string 0.1nm to express Angströms (Å=10-10m), since the Angström is a non-standard unit. Another example is mW/m2 , the milliwatt per m2, which is identical to the CGS erg/cm2/s unit and is not used outside astronomy.
Unit syntax should abide by the following rules:
When possible choose the shortest syntax. For example, km/s to km.s-1.
Only simple power functions of physical units are accepted, which means that e.g. solMass3/2 (solar mass at a 3/2 power) is not valid. However for units expressed on a base 10 logarithmic scale, use bracketed units such as [solMass] to indicate logM{sun}.
Note that a more extensive list of allowed units is available here.
Symbol | Explanation | Definition | |
---|---|---|---|
(c) | -- | Unitless value | |
(c) | % | Unitless value, in percent | 10-2 |
(a) | a | year (also yr) | 365.25d = 31.5576×106s |
(b) | A | Ampere | |
(a) | AU | astronomical unit | 1.49598×1011m |
(a) | arcmin | minute of arc | 1/60 ° |
(a) | arcsec | second of arc | 1/60 arcmin |
(e) | barn | barn (cross-section) | 10-28 m2 |
(c) | bit | binary information unit (computer storage) | |
(c) | byte | byte (computer storage) | 8 bit |
C | Coulomb (electric charge) | A·s | |
(b) | cd | Candela (luminous intensity) | |
(c) | ct | Count (events) | |
D | Debye | (1/3)×10-29 C·m | |
(a) | d | day | 24h = 86.4×103s |
(a) | deg | degree of arc (°) | {pi}/180 rad |
(e) | eV | electron-Volt | 1.602177×10-19 J |
F | Farad (electric capacitance) | C/V | |
(b) | g | gram | 10-3 kg |
(a) | h | hour of time (sideral if appropriate) | 3600s |
H | Henry (inductance) | Wb/A | |
Hz | Hertz (frequency) | s-1 | |
J | Joule (energy) | N·m | |
(a) | Jy | Jansky | 10-26 W/m2/Hz |
(b) | K | Kelvin | |
lm | lumen (luminous flux) | cd·sr | |
lx | lux (illuminance) | lm/m2 | |
(b) | m | metre | |
(a) | mag | magnitudes | |
(a) | mas | millisecond of arc | ({pi}/6.48)×10-8 rad |
(a) | min | minute of time (sideral if appropriate) | |
(b) | mol | mole | |
N | Newton (force) | kg·m/s2 | |
Ohm | ({Omega}) Ohm (electric resistance) | V/A | |
Pa | Pascal (pressure) | N/m2 | |
(a) | pc | parsec | 3.0857 ×1016m |
(c) | pix | pixel (image element) | |
(b) | rad | radian (angle) | |
(e) | Ry | Rydberg (energy) | (1/2) (2{pi}e2/hc)2mec2 = 13.60583 eV |
(b) | s | second of time | |
S | Siemens (electric conductance) | A/V | |
(c) | solLum | Solar luminosity | 3.826×1026 W |
(c) | solMass | Solar mass | 1.989×1030 kg |
(c) | solRad | Solar radius | 6.9599×108 m |
(c) | Sun | Unit referring to the Sun (e.g. abundances) | |
sr | steradian (solid angle) | ||
T | Tesla (magnetic field intensity) | Wb/m2 | |
V | Volts (electric potential) | W/A | |
W | Watt (power) | J/s | |
Wb | Weber (magnetic flux) | V·s | |
(c) | yr | year (also a) | 365.25d = 31.5576×106s |
The basic symbols listed include basic standard SI units (b), the extensions listed by the IAU style book marked (a), other frequent physical extensions (e), and a few further astronmical extensions (c).
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