*English-Metric Conversions*
inch (in) = 2.54 cm (exactly)

meter (m) = 39.37008 in (approximately)

mile (mi) = 1.609344 km (exactly)

kilometer (km) = 0.6213712 mi (approximately)

pound (lb) = 453.6 g = 0.4536 kg

kilogram (kg) = 2.205 lb

*(Perhaps Unfamiliar) Units*
atmosphere (unit of pressure) = average atmospheric pressure at the surface of the Earth

= 14.7 pounds per square inch ~ 2120 pounds per square foot ~ one tonne per square foot

bar (unit of pressure) = 10 Newtons per square centimeter (~ one atmosphere)

Pascal (unit of pressure) = 1 Newton per square meter = 1/100,000th of a bar

*Distances*
Astronomical Unit (AU) = 149,597,870.691 km = 92,955,807.267 mi

Semi-major axis of Earth's orbit = 149,597,890 km = 92,955,819.3 mi =

1.00000013 AU
Light year (LY) = 9.46053 trillion km = 5.87850 trillion mi = 63,239.7 AUs = 0.30660 pc

Parsec (pc) = 1296000 / 2 π AUs = 206264.8062 AUs = 30.856776 trillion km = 19.1735 trillion mi

Parsec (pc) = 3.2616 LY

*Time Units*
**Rotational periods of the Earth** (all increasing by 0.002 seconds/day/century)

Relative to fixed stars = 23 hr 56 m 4.099 s

Mean sidereal day (relative to Vernal Equinox) = 23 hr 56 m 4.091 s

Mean solar day (relative to Sun, average over a year) = 24 hr 00 m 0.000 s in 1900

**Orbital periods of the Earth**
Sidereal year (Relative to fixed stars) = 365.256363 Mean solar days

Tropical year (Relative to Vernal Equinox) = 365.242190 days = 365d 05h 48m 45.2s = 31,556,925.2 s

Anomalistic year (Relative to perihelion) = 365.259635 days

Eclipse year (Relative to Moon's ascending node) = 346.620075 days in 1999 (+0.000001 days/year)

*Astronomical Bodies*
equatorial radius of the Earth (

*R*_{Earth}) = 6378.1 km = 3963.2 mi

mass of the Earth (

*M*_{Earth}) = 5.9736 x 10

^{24} kg

equatorial radius of the Sun (

*R*_{☉}) = 696000 km = 432000 mi = 109

*R*_{Earth}
mass of the Sun (

*M*_{☉}) = 1.989 x 10

^{30} kg = 333000

*M*_{Earth}
luminosity of the Sun (

*L*_{☉}) = 3.85 x 10

^{26} watts = 5.9 million watts/square foot

surface temperature of the Sun (

*T*_{☉}) = 5780 Kelvin = 9950 Fahrenheit

*Fundamental Physical Constants*
(Units: s = second, J = joule, K = Kelvins, kg = kilograms, m = meters, W = watts)

Avogadro constant (

*N*_{A}) = 6.0221420 x 10

^{23} mol

^{-1}
Boltzmann constant (

*k*) = 1.380650 x 10

^{-23} J K

^{-1}
elementary charge (

*e*) = 1.602176462 x 10

^{-19} Coulombs

electron volt (eV) = 1.602176462 x 10

^{-19} J

molar gas constant (

*R*) = 8.31447 J mol

^{-1} K

^{-1}
Newtonian gravitational constant (

*G*) = 6.67 x 10

^{-11} m

^{3} kg

^{-1} s

^{-2}
Planck constant (

*h*) = 6.6260688 x 10

^{-34} J s

Planck length (

*l*_{P}) = 1.616 x 10

^{-35} m

Planck time (

*t*_{P}) = 5.3906 x 10

^{-44} s

Speed of light in a vacuum (

*c*) = 299,792.458 km/sec (exactly) =186,282.397 mi/sec (approximately)

Stefan-Boltzmann constant (

**σ**) = 5.6704 x 10

^{-8} W m

^{-2} K

^{-4}
*Masses of fundamental particles*
atomic mass unit (

*m*_{u}) = 1.6605387 x 10

^{-27} kg

electron mass (

*m*_{e}) = 9.1093819 x 10

^{-31} kg

proton mass (

*m*_{p}) = 1.6726216 x 10

^{-27} kg = 1836.152668

*m*_{e}
alpha-particle mass (

*m*_{α}) = 6.6446560 x 10

^{-27} kg = 3.9725997

*m*_{p}