Summary

After having studied this lecture, you should be able to

• Describe the Great Debate, give the points in favour of each camp, and discuss the problems with their arguments.
• Derive the relation between the stellar density and star counts
• Explain what a standard candle is.
• Explain why Cepheids and RR Lyrae variables are good standard candles.
• Explain what parallax is, and know how the distance to nearby stars can be measured using their parallax.
• Explain how parallax and Cepheids can be used to walk-up the distance ladder.
• Explain how Hubble's observations revolutionised our view of the MW and the realm of the Nebulae.
• Derive the effect of scattering by dust on the apparent magnitude and colour of distant stars. Know the approximate value of the interstellar absorption in the MW.