Astronomy Flashcards
Luminosity
The total power of electromagnetic radiation emitted by the star
What is ‘radiant flux intensity’ (F) as observed from Earth?
The power per unit area of electromagnetic radiation received from the star
Write the equation that relates luminosity (L), radiant flux intensity (F), and the distance (d) to a star.
F = L / (4πd²)
What term is used to describe an astronomical object with a known luminosity?
A standard candle
An example of a standard candle
Cepheid Variable stars
Key characteristic of Cepheid variable stars that makes them useful as standard candles?
Their luminosity varies periodically with a predictable relationship between their period of variation and their average luminosity
How can astronomers use Cepheid variables to estimate the distances to galaxies?
By measuring their period of brightness variation, determining their luminosity using the period-luminosity relationship, and then using the measured radiant flux intensity on Earth in the inverse square law
State Wien’s displacement law (qualitatively)
The wavelength at which the intensity of black body radiation is maximum (λ_max) is inversely proportional to the absolute temperature (T) of the body
Write the equation for Wien’s displacement law
λ_max = b / T, where b is Wien’s displacement constant
State the Stefan-Boltzmann law
L = 4πr²σT⁴, where σ is the Stefan-Boltzmann constant
What is typically observed in the spectra of light from most distant galaxies?
A redshift, meaning the wavelengths of the spectral lines are shifted towards longer wavelengths
What phenomenon explains the observed redshift of light from distant galaxies?
The Doppler effect
Write the approximate equation relating the Doppler shift of light to the recession velocity of a galaxy.
Δλ / λ ≈ v / c, where Δλ is the change in wavelength, λ is the emitted wavelength, v is the recession velocity, and c is the speed of light
State Hubble’s Law.
The recession velocity (v) of a galaxy is directly proportional to its distance (d) from the observer
Write the equation for Hubble’s Law
v ≈ H₀d, where H₀ is Hubble’s constant
What is the primary conclusion drawn from the observation of redshift in the spectra of most galaxies and Hubble’s Law?
The universe is expanding
How can Hubble’s constant (H₀) be used to make a rough estimate of the age of the universe?
The approximate age of the universe can be estimated as 1 / H₀
