Astronomy and cosmology

You will be able to

• Use the inverse square law F = L / (4πd²) for the radiant flux intensity at a distance d from a source of luminosity L.
• Predict how the radiant flux intensity changes when the distance from a star changes.
• Determine the distance to a standard candle from its luminosity and measured radiant flux intensity, and explain why the luminosity must be known.

You will be able to

• Use Wien's displacement law λmax T = 2.9 × 10⁻³ m K to find the surface temperature of a star from the peak of its spectrum.
• Use the Stefan–Boltzmann law L = 4πσr²T⁴ to determine the radius of a star.
• Explain why hotter stars appear blue and cooler stars red.

You will be able to

• Calculate the recession speed of a galaxy from the redshift of a spectral line using Δλ / λ ≈ Δf / f ≈ v / c.
• Determine the Hubble constant H₀ from the gradient of a graph of recession speed against distance, in s⁻¹ and km s⁻¹ Mpc⁻¹.
• Estimate the age of the Universe as 1 / H₀ and explain how Hubble's law supports the Big Bang theory.