Edexcel astronomy gcse equations

the Equation of Time

the Equation of Time = Apparent Solar Time (AST) − Mean Solar Time (MST)

Be able to use Kepler's third law

T² / r³ = a constant

where T is the orbital period of an orbiting body and r is the mean radius of its orbit

Magnification of a telescope

Magnification of a telescope = fₒ / fₑ

Be able to use the distance modulus formula to determine the absolute (M) or apparent magnitude (m) of a star, given the distance to the star (d)

M = m + 5 - 5logd

where d is the distance in parsec

Redshift

( λ - λ₀ ) / λ₀ = v / c

where λ is the observed wavelength, λ₀ is the emitted wavelength, v is the radial velocity of the source, c is the speed of light

Hubbles law

dH₀v = 0

where v is the radial velocity of the recession of the galaxy, H₀ is the Hubble constant and d is the distance of the galaxy from Earth