Units and Constants

Contents

Multiplication Factors

Common Names in SI Units

SI and British (fps) Unit Conversions

Unit Conversions

• 1 ly. (light year) = 10¹⁸ cm
• 1 pc. (parsec) = 3 ly. = 3x10¹⁸ cm
• 1 AU = 1.496x10¹³ cm
• 1 m (meter) = 100 cm
• 1 micron = 10^-4 cm
• 1 ml = 1 cm³
• 1 liter = 1000 ml
• 1 knot = 1.15 mi/hr = 1.85 km/hr
• Temperature T (in ^oC) = T (in ^oK) - 273.15
• Temperature T (in ^oF) = 1.8 x T (in ^oC) + 32
• 1 ev (electron volt) = 1.602x10^-12 erg
• 1 joule = 10⁷ ergs
• 1 watt = 1 J/sec = 10⁷ erg/sec
• 1 mi/gal = 0.354 km/liter

Physical Constants

• Velocity of light c = 2.998x10¹⁰ cm/sec
• Gravitational Constant G = 6.67x10^-8 cm³/sec²-gm
• Hubble constant H_o = 7.1 km/sec-Mpc
• Luminosity of the Sun = 3.86x10³³ erg/sec
• Mass of the Sun = 2x10³³ gm
• Distance from Sun to Earth = 1 AU = 1.5x10¹³ cm
• Flight time of light from Sun to Earth = 499 sec
• Solar constant = 1.388x10⁶ erg/cm²-sec
• Diameter of the Earth = 1.3x10⁹ cm
• Mass of the Earth = 6x10²⁷ gm
• Mean radius of the Earth = 6371 km
• Standard acceleration of gravity = 980.6 cm/sec²
• 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 = 6.023x10²³ molecules/mole
• Normal volume of pergect gas = 2.241x10⁴ cm³/mole
• kT = 0.0258 ev at T = 300^oK
• Gas constant = 8.314x10⁷ 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 = 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

Cosmological Constants (WMAP)

Misc.

• mega = 10⁶, million = 10⁶, billion = 10⁹.
• Astronomical symbols:
  



• Nomenclature of Binary Molecules (compounds of only two elements, e.g., H₂O, HCl) :
  1. For covalent molecules, element to the left and below in the periodic table (see Figure 12-19) is named first. For example, in HCl hydrogen is named first, and in BrCl bromine is named first. For ionic molecules, cation (positively charged element) is named first.
  2. For covalent molecules, the other element is named with "-ide" ending. For example, HCl is named hydrogen chloride, and BrCl is named bromine chloride. For ionic molecules, anion (negatively charged element) is ended with "-ide".
  3. When two non-metals form more than one compound from each other, Greek prefixes are used. (Note: mono- is not affixed to first element of compound if there is only one atom per molecule, e.g., CO₂ is carbon dioxide, not monocarbon dioxide). For example, the prefix for one=mono-, two=di-, three=tri-, four=tetra-, five=penta-, six=hexa-, seven=hepta-, eight=octa-, nine=nona-, and ten=deca-. Therefore, the names for the following compounds are: NO - nitrogen monoxide, N₂O - dinitrogen monooxide, NO₂ - nitrogen dioxide, N₂O₃ - dinitrogen trioxide, N₂O₄ - dinitrogen tetroxide, N₂O₅ - dinitrogen pentoxide, PCl₅ - phosphorus pentachloride, P₂O₅ - diphosphorus pentoxide, SF₆ - sulfur hexafluoride, and Cl₂O₇ - dichlorine heptoxide.