Constants:

1. fundamental physical constants AKA fundamental constants AKA physical constants:
   1. Avogadro's number = 6.02214076*10**23 (exact) (see NIST: Fundamental Physical Constants)
   2. Boltzmann contant k = 1.380649*10**(-23) J/K = (0.8617333262 ... )*10**(-4) eV/K (exact) ≅ 10**(-4) eV/K = 10**(-10) Mev/K (see NIST: Fundamental Physical Constants)
   3. electron-volt (eV) = 1.602176634*10**(-19) J (exact) 1 eV = 1.602176634*10**(-19) J (see NIST: Fundamental Physical Constants)
   4. Fine-structure constant α = e**2/(ħc) = 1/[137.035999084(21)] ≅ 1/137 (see NIST: Fundamental Physical Constants)
   5. g = 9.80665 m/s**2 standard acceleration of gravity (exact) ≅ 9.8 m/s**2 (fiducial value) (see NIST: Fundamental Physical Constants)
   6. gravitational constant G = 6.67430(15)*10**(-11) (MKS units) (see NIST: Fundamental Physical Constants)
   7. hc = 1.239841984*10**(-6) eV-m = 1.239841984*10**(-4) eV-cm (exact) (see NIST: Fundamental Physical Constants)
   8. Planck's constant h = 6.62607015*10**(-34) J-s = (4.135667696 ...) *10**(-15) eV-s (exact) (see NIST: Fundamental Physical Constants)
   9. radiation density constant a=4σ/c = (7.5657332500339 ...)*10**(-16) J/m**3/K**4 (exact) = (1 J/m**3)(1/6029.6164961230 ... K)**(1/4) (see NIST: Fundamental Physical Constants))
   10. reduced Planck's constant ħ = (1.054571817 ...)*10**(-34) J-s = (6.582119569 ...)*10**(-16) eV (exact) (see NIST: Fundamental Physical Constants --- Complete Listing) (pronounced h-bar)
   11. second radiation constant hc/k = (1.438 776 877...)*10**(4) μm-K (see NIST: Fundamental Physical Constants)
   12. Stefan-Boltzmann constant σ = (5.670 374 419 ...)*10**(-8) W/*m**2/K**4 (exact) (see NIST: Fundamental Physical Constants)
   13. vacuum light speed c = 2.99792458*10**8 m/s = 2.99792458*10**5 km/s (exact) ≅ 3*10**5 km/s, (see NIST: Fundamental Physical Constants)
   14. Wien's law constant = 2897.771955 ... μm-K (see NIST: Fundamental Physical Constants)
2. natural units:
   1. mega-square-kilometer = Mk = 10**6 km**2: This is the natural unit for the Earth surface area since its total is 510.072 Mk = 510072000 km**2 ≅ 510 Mk (see Wikipedia: Earth: Side table). Note:

       
          1 Mk = (10**3 km)**2 = 10**2 pMk (for percent of an MK)
               1 pMk = (100 km)**2 = 10**4 km**2
               1 km**2 = 100 ha
               1 ha = (100 m)**2 = (1/100) km**2
               10**6 ha = 10**4 km**2 = 1 pMk
          

      Fiducial surface areas:
      1. bodies of water:
         1. Lake Erie: 2.5667 pMk.
         2. Pacific Ocean: 165.250 Mk ≅ (1/3) of Earth's 510.072 Mk.
      2. countries, etc.:
         1. Australia: 7.692024 Mk.
         2. Bermuda: 53.2 km**2.
         3. Canada: 9.984670 MK ≅ 10 Mk. Includes water area.
         4. China: 9.596961 Mk. Excludes disputed areas.
         5. Ecuador: 0.0283561 Mk = 28.3561 pMk.
         6. Ireland: 0.084421 Mk = 84.421 pMk ≅ 0.1 Mk.
         7. Monaco: 2.2 km**2 = 220 ha.
         8. Nauru: 21 km**2.
         9. Russia: 17.098246 Mk.
         10. United States of America (USA): 9.833517 Mk. Includes water area.
      3. Earth: 510.072 Mk.
      4. Moon: 37.93 Mk ≅ 0.074 of Earth's.

File: Physics file: constants.html.