# Constants
# Coryn Bailer-Jones, 2025

# angular quantities
conv <- pi/180 # degrees -> radians
arcsec <- (pi/180)/3600  # arcsecond in radians

# natural constants in SI units
cc  <- 299792458       # speed of light
ee  <- 1.60217657e-19  # electron charge
hh  <- 6.626176e-34    # Planck's constant
kk  <- 1.380649e-23    # Boltzmann's constant [J K^-1]
GG  <- 6.67428e-11     # gravitational constant
me  <- 9.1093836e-31   # electron mass
mu  <- 1.66053904e-27  # atomic mass unit
Nav <- 6.02214076e23   # Avogadro's constant [mol^-1] # = 1e3/mu

# derived constants in SI units
sbc <- 2*pi^5*kk^4/(15*cc^2*hh^3) # Stefan-Boltzmann constant, approx. 5.670103e-8.  
ugc <- kk*Nav # universal gas constant [J K^-1 mol^-1]

# physical quantities [SI]
km <- 1e3   
day <- 86400

# solar system body parameters, SI
ssb <- data.frame(row.names=c("sun", "venus", "earth", "moon", "mars", "jupiter"),
                  mass=c(1.989e30, 4.8675e24, 5.9736e24, 7.342e22, 6.4185e23, 1.8982e27),
                  radius=c(6.957e8, 6.0518e6, 6.378e6, 1.7381e6, 3.396e6, 7.1492e7), # equatorial
                  rotper=c(2.164e6, 2.099736e7, 8.616509e4, 2.360592e6, 8.864267e4, 3.573e4)) # sidereal
ssb$rgeo <- (GG*ssb[,"mass"]*ssb[,"rotper"]^2/(4*pi^2))^(1/3) # geostationary radius
ssb$surgrav <- GG*ssb[,"mass"]/ssb[,"radius"]^2               # surface gravity acceleration
ssb$density <- ssb[,"mass"]/((4*pi/3)*ssb[,"radius"]^3)       # mean density using *equatorial* radius

# Solar system constants
sgp   <- 1.32712440018e20       # standard gravitational constant in SI (=G*msun, but better determined)
yr    <- 365.25*24*3600         # length of Julian year in SI (s). Tropical year is 365.242190 days
au    <- 1.495978701e11         # au in SI (m) (Hipparcos catalogue documentation p. 25, Table 1.2.2)
pc    <- (3600*180/pi)*au       # parsec in SI (m) [3.085678e+16]
kf    <- au/(yr*km)             # 1 au/yr in km/s. Units: km s^-1 yr [4.740471]
                                # converts proper motion of 1as/yr at 1pc to velocity in km/s 
ly    <- cc*yr                  # light year (using Julian year) in SI
lsun  <- 3.828e26               # luminosity of Sun in SI
sidyr <- 365.256363004*24*3600  # sidereal year in SI (s)

# Approximate nucleus masses, in atomic mass units (mu = 1.66053904e-27 kg)
# Source: https://wwwndc.jaea.go.jp/NuC/
# which gives atomic masses, so I then subtract the mass of the electrons 
# (ignoring electron binding energy). one electron mass is mu/me = 0.00054858.
# See also https://chemlin.org/isotope/hydrogen-2
nucmass <- list(n=1.00866492,
                H=1.00727645, H2=2.01355320, H3=3.01550070, 
                He3=3.01493216, He4=4.00150609)

# Material constants
muzero  <- 1.256637062e-6 # vacuum permeability in SI (H m^-1; M L T^-2 I^-2)
epszero <- 8.85418781e-12 # vacuum permittivity in SI (F m^-1; M^-1 L^-3 T^4 I^-2)