# 13: Equations Flashcards

Ratio of Δλ to λ

Δλ/λ = v/c, if v «_space;c

Δλ = difference between the observed wavelength and emitted wavelength

λ = emitted wavelength

v = velocity if the source

c = speed of light

the double less than means ‘much less than’

the velocity of something must be much less than the speed of light to avoid relativistic effects

Velocity = (Hubble’s constant)

v = H₀d v = recessional velocity H₀ = Hubble's constant d = distance

In the equation v = H₀d, what unit is velocity?

kms⁻¹

In the equation v = H₀d, what unit is Hubble’s constant?

kms⁻¹Mpc⁻¹

In the equation v = H₀d, what unit is distance?

Mpc, megaparsec

What is 1 Mpc in m

3.09 * 10²²

Relativity t =

t = λτ

where t = actual time (longer)

τ = expected time w/o relativity (shorter)

λ = relativistic factor (always greater than 1)

equation with radar for working out distance to object

2d = ct

break down realivistic factor t = (1)t0 / sqr(1 - v²/c²)

t = longer interval

t0 = proper time

v = constant velocity

t0 can also be 1

how to calculate age of universe in years if given a value for hubbles constant of 300km s^-1 mpc^-1

mpc^-1 = 3.1 * 10^22

first convert that velocity into ms^-1 and divide by value of megaparsec to get hubble’s constant in seconds

then do timescale = 1 / hubbles constant to get age of universe in seconds

then divide this timescale in seconds by 3.16 * 10^7 (seconds in year) to get timescale for age of universe in years