Messages From Above
If I glance at your passport, I am able to figure out — depending on where you are from — your age, your country of origin, your full name, your social security number, and your gender, among other things, and in order to retrieve these bits of information from your passport, I need first and foremost to be able to read the language in which the information is written.
By the same token, the light that reaches us from stars carries a goldmine of data about their individual characteristics, and it is stellar spectroscopy that allows us to uncover and read these properties from the emitted light.
Some of the physical quantities that can be extracted by studying starlight include the temperature of the outer layer of the star, the nature and the relative amount of the chemical substances present, the luminosity, the density, and the star’s motion with respect to our position. Other pieces of information that can be obtained either directly or indirectly are the mass and size of the star, its rotational speed, the presence of any magnetic fields, stellar winds, or orbiting partners, as well as the distribution of matter around the star.
This article embraces three aspects in particular: the nature of matter (the chemical composition), the temperature, and the relative motion.
