Home Page |
Overview |
Site Map |
Index |
Appendix |
Illustration |
About |
Contact |
Update |
FAQ |

Common Names in SI Units

SI and British (fps) Unit Conversions

Unit Conversions

Natural Units

Physical Constants

Scales of the Universe

Cosmological Constants (WMAP)

Astronomical Symbols

Greek Alphpbets, and Linguistics

mega = 10

- 1 ly. (light year) = 10
^{18}cm - 1 pc. (parsec) = 3.26 ly
- 1 AU = 1.496x10
^{13}cm - 1 m (meter) = 100 cm
- 1 micron = 10
^{-4}cm - 1 ml = 1 cm
^{3} - 1 liter = 1000 ml
- 1 knot = 1.15 mi/hr = 1.85 km/hr
- Temperature T (in
^{o}C) = T (in^{o}K) - 273.15 - Temperature T (in
^{o}F) = 1.8 x T (in^{o}C) + 32 - 1 ev (electron volt) = 1.602x10
^{-12}erg - 1 joule = 10
^{7}ergs - 1 watt = 1 J/sec = 10
^{7}erg/sec - 1 mi/gal = 0.354 km/liter

Physical Quantity | SI Unit | Transition to cm | Natural Unit (cm) | Transition to erg | Natural Unit (erg) |
---|---|---|---|---|---|

Velocity of Light (c) | 2.998x10^{10} cm/sec |
1 | 1 | ||

Planck's Constant () | 1.055x10^{-27} erg-sec |
1 | 1 | ||

Time | sec | cm/c | cm | erg^{-1} |
erg^{-1} |

Length | cm | cm | cm | (c) erg^{-1} |
erg^{-1} |

Energy | erg | (c) cm^{-1} |
cm^{-1} |
erg | erg |

Mass | gm | (/c) cm^{-1} |
cm^{-1} |
erg/c^{2} |
erg |

Momentum | gm-(cm/sec) | cm^{-1} |
cm^{-1} |
erg/c | erg |

Angular Momentum | gm-(cm/sec)-cm | 1 | 1 | ||

Velocity | cm/sec | c | 1 | c | 1 |

Charge | (erg-cm)^{1/2} |
(c)^{1/2} |
1 | (c)^{1/2} |
1 |

Gravitational Constant | cm^{3}/gm-sec^{2} |
(c^{4}/c) cm^{2} |
cm^{2} |
c^{4}(c) erg^{-2} |
erg^{-2} |

- There are three examples below to show how to run a reversed conversion from natural unit to SI units :
- Electromagnetic Wave Equation -

In natural unit of [cm] (the unit is enclosed within the bracket [ ]) this equation is in the form :

^{2}**E**-_{}**E**= 0

Conversion back to SI units in this case is very simple by substituting the natural unit [cm]^{2}with the SI units c^{2}[sec]^{2}in the denominator of the second term. Then the equation in SI units is recovered as:

^{2}**E**- (1/c^{2})_{}**E**= 0 - Total Energy -

E = (m^{2}+**p**^{2})^{1/2}

In natural unit of [erg], unit of m is converted back to SI by c^{2}[gm], while the conversion for unit of**p**is c[gm-cm/sce]. Therefore the formula in SI is :

E = (m^{2}c^{4}+**p**^{2}c^{2})^{1/2} - Schrodinger Equation -

In natural unit it has the form : -(1/2m)_{}= i_{}

Converting from the natural unit of [erg], the left-handed side produces a factor of (1/c^{2}[gm])(c/[cm])^{2}=^{2}/[gm-cm^{2}]. On the right-handed side the converting factor is /[sec]. Combining everything together, we recovered the equation in SI :

-(^{2}/2m)_{}= i_{}

Incidentally, for all cases the same form in SI units will be recovered whether the natural unit is in [cm] or [erg].

- Velocity of light c = 2.998x10
^{10}cm/sec - Gravitational Constant G = 6.6742x10
^{-8}cm^{3}/sec^{2}-gm = 6.7087x10^{-39}c (Gev / c^{2})^{-2} - Hubble constant H
_{o}= 7.1 km/sec-Mpc - Hubble parameter (dimensionless) h = H
_{o}/100 - Luminosity of the Sun = 3.86x10
^{33}erg/sec - Mass of the Sun = 2x10
^{33}gm - Distance from Sun to Earth = 1 AU = 1.5x10
^{13}cm - Flight time of light from Sun to Earth = 499 sec
- Solar constant = 1.388x10
^{6}erg/cm^{2}-sec - Diameter of the Earth = 1.3x10
^{9}cm - Mass of the Earth = 6x10
^{27}gm - Mean radius of the Earth = 6371 km
- Standard acceleration of gravity = 980.6 cm/sec
^{2} - 1
^{o}of latitude = 110.5 km (at equator) = 111.7 km (at poles) - 1
^{o}of longitude at equator = 111.3 km - Planck's constant = 6.625x10
^{-27}erg-sec = 4.136x10^{-15}ev-sec - Avogadro's number = 6.023x10
^{23}molecules/mole - Normal volume of pergect gas = 2.241x10
^{4}cm^{3}/mole - kT = 0.0258 ev at T = 300
^{o}K - Gas constant = 8.314x10
^{7}erg/K^{o}-mole - Boltzmann constant = 1.38x10
^{-16}erg/K^{o} - Speed of sound = 34000 cm/sec
- Electronic charge = 1.602x10
^{-19}coul - Fine-structure constant = e
^{2}/c = 1/137 - Bohr radius = 5.29 nm
- Mass of unit atomic weight = 1.6603x10
^{-24}gm - Nucleon rest mass = 1.67x10
^{-24}gm - Electron rest mass = 9.109x10
^{-28}gm

## WMAP Cosmological Parameters [view large image] |

The WMAP team has released the final evaluation of the cosmological parameters on December 2012. These new values has been copied to the table (on 7-year results) above. In addition, the 9-year observations have confirmed the add-on of inflation to the Bing Bang model with tiny fluctuations growing to form the galaxies. The data also confirm that the universe is flat. See all the details in NASA/WMAP News.