Summary

After having studied this lecture, you should be able to

• Describe how radio and infra-red observations are being used to clarify our picture of the MW.
• Explain how the Hipparcos satellite was a major step in setting the scale of the MW, by performing accurate parallax and proper motions measurements, and fixing a reference frame with respect to distant objects.
• Describe the main components of the MW, thin and thick disk, bulge and bar, stellar halo, and their typical properties such as their density and luminosity profiles.
• Explain what is meant by the metallicity of a star, and know what is meant by the notation [Fe/H]=-1.
• Know how the Galactic Coordinate system $(l,b)$ is defined, know the direction to the galactic centre $l=b=0$, and the galactic plane $\vert b\vert<5^o$.