λ | Wavelength | µm | Wavelength of the incident solar radiation |

γ | Angular distance | arc min | Angular distance from the center of the Earth’s shadow |

R_{S} | Angular radius | arc min | Angular radius of the Sun |

R | Angular distance | arc min | Angular distance from the center of the solar disk |

ɛ_{0} | Angle | arc min | Maximum angle under which the elementary ring at the solar disk is visible from point E′ (Fig. 1) |

ɛ | Angle | arc min | Angle that defines the position of a certain point at the elementary ring (Fig. 1) |

ρ | Angular distance | arc min | Angular distance of the elementary ring from point E′ (Fig. 1) |

π_{S} | Parallax of the Sun | arc min | Angle subtended by the Earth’s equatorial radius at the center of the Sun at the mean distance between Earth and the Sun |

π_{M} | Parallax of the Moon | arc min | Angle subtended by the Earth’s equatorial radius at the center of the Moon at the mean distance between the Earth and the Moon |

dS | Area | km^{2} | Surface at the lunar plane illuminated by flux of light when no refraction takes place in the Earth’s atmosphere |

dS′ | Area | km^{2} | Surface at the lunar plane illuminated by flux of light when refraction takes place in the Earth’s atmosphere |

κ_{λ} | Coefficient dependent on the wavelength | Dimensionless | Coefficient that characterizes the luminosity distribution at the solar disk |

c_{λ} | Light dispersion | Dimensionless | Coefficient that refers to the light dispersion in the Earth’s atmosphere |

h_{0} | Altitude | km | Minimum altitude of the ray in the Earth’s atmosphere |

h | Altitude | km | Altitude of the general point on the sunbeam trajectory |

ℜ | Radius of the Earth | km | Radius of the Earth |

H | Scale height | km | Altitude up to which a homogeneous molecular atmosphere would extend |

ρ_{G} | Air density | kg m^{−3} | Air density at the ground |

r | Particle radius | µm | Radius of the particle |

r_{m} | Particle modal radius | µm | Modal radius of the particle size distribution function f(r) |

a | Parameter of the particle size distribution function | Dimensionless | Refers to modified gamma size distribution function f(r) ∼ r^{a}e^{−}^{br} |

b | Parameter of the particle size distribution function | µm^{−1} | Refers to modified gamma size distribution function f(r) r^{a}e^{−}^{br} |

B | Euler angle | rad | Specify the particle’s orientation with respect to the laboratory reference frame |

Θ | Euler angle | rad | Specify the particle’s orientation with respect to the laboratory reference frame |

Φ | Euler angle | rad | Specify the particle’s orientation with respect to the laboratory reference frame |

m | Refractive index | Dimensionless | Complex refractive index of the particle |

x | Size parameter | Dimensionless | Size parameter defined as 2πr/λ |

e_{λ}(γ) | Relative irradiance | Dimensionless | Irradiance of a certain point at distance γ from the center of the Earth’s shadow (including atmospheric effects) |

E_{λ}(γ) | Relative irradiance | Dimensionless | Irradiance of a certain point at distance γ from the center of the Earth’s shadow (excluding atmospheric effects) |

D_{λ}(γ) | Optical density | Dimensionless | Negative common logarithm of the ratio of irradiances E_{λ}(γ) and e_{λ}(γ) (Fig. 1) |

b_{λ}(ρ, ɛ) | Relative luminosity | Dimensionless | Relative amount of energy the element at the solar surface radiates in unit time |

ω(h_{0}) | Angle of refraction | arc min | Refraction of the rays of light passing through the atmosphere horizontally |

i_{λ}(h) | Apparent zenith angle | rad | Angle subtended at a general point on the trajectory by its radius vector with the ray (Fig. 1) |

T^{ref}(h_{0}) | Transmission coefficient | Dimensionless | Factor by which the radiation flux is reduced (due to atmospheric refraction) when reaching altitude h_{0} |

T^{ext}(h_{0}) | Transmission coefficient | Dimensionless | Factor by which the radiation flux is reduced (due to atmospheric extinction) when reaching altitude h_{0} |

T^{air} | Transmission coefficient | Dimensionless | Factor by which the radiation flux is reduced (due to molecular scattering) when reaching altitude h_{0} |

T^{ozone} | Transmission coefficient | Dimensionless | Factor by which the radiation flux is reduced (due to ozone absorption) when reaching altitude h_{0} |

T^{aerosol} | Transmission coefficient | Dimensionless | Factor by which the radiation flux is reduced (due to aerosol extinction) when reaching altitude h_{0} |

δ_{λ}(h) | Aerosol coefficient | Extinction km^{−1} | Fraction of radiant flux lost from a collimated beam per unit thickness of aerosol |

α_{λ}(h) | Ozone coefficient | Extinction km^{−1} | Fraction of radiant flux lost from a collimated beam per unit thickness of ozone due to absorption |

β_{λ}(h) | Rayleigh coefficient | Extinction km^{−1} | Fraction of radiant flux lost from a collimated beam per unit thickness of air molecules due to scattering |

τ_{λ}(h_{0}) | Aerosol optical thickness | Dimensionless | Negative natural logarithm of ratio of incident radiant flux and the flux transmitted through aerosol environment |

C_{ext}(λ, r) | Extinction cross section | µm^{2} | This quantity equals the total monochromatic power removed by the particle from the incident beam divided by the incident monochromatic energy flux |

Q_{ext}(λ, r) | Efficiency coefficient for extinction | Dimensionless | Dimensionless quantity defined as a ratio of C_{ext}/πr^{2} (for spherical particles of radii r) |

f_{h}_{0}(r) | Particle size distribution | µm^{−3} | Columnar aerosol size distribution function at base altitude h_{0} |

S_{h}_{0}(r) | Particle size distribution | µm^{−1} | Columnar surface aerosol size distribution function at base altitude h_{0} |

s(r, h) | Particle size distribution | m^{−2} | Altitude-dependent particle size distribution function |