HOW DO WE STUDY STARS?

Reading: Chapters 17 (The Nature of Stars) and 3 and 4 (The Nature of Light)

Astrophysics is a difficult observational science for many reasons. For example,

• Stars are distant which makes ordinary experiments impossible. The nearest star is Proxima Centauri. It is at a distance of 4.3 light years ~ 40 trillion kilometers from us. Traveling at the speed of the typical interplanetary probe, ~ 20 kilometers per second, it would take 70,000 years to travel to Proxima Centauri!

• We cannot control stars. We cannot design experiments we would like to perform. We must observe what nature gives to us.

• ....

How Do We Study Stars?

Most observations of Celestial Objects are made using Optical Telescopes (I will define optical formally in a little bit. For now take optical to mean the type of light to which our eyes are sensitive) located at ground-based observatories (e.g., Kitt Peak National Observatory, Cerro Tololo Inter-American Observatory, National Solar Observatory, ... ) and orbiting observatories, the Hubble Space Telescope.

Much information about the Universe has been gleaned from optical observations, however, much more can be learned if we consider things other than optical light; objects in the Universe produce many other forms of radiation (collectively, the overall radiation phenomenon is referred to as Electromagnetic radiation). Until recently, however, this information was not utilized, because

that is most types of radiation cannot penetrate the Earth's atmosphere. Today, we can place telescopes into orbit about the Earth and so are able to study stars across all portions of the electro-magnetic spectrum -- we now study stars and other celestial objects from the radio to the gamma-ray.

Further, we can also study stars using the matter (particles) that they produce, e.g., the Solar Neutrino Experiment studies the particle emission from the Sun. There are also experiments which try to detect the gravitational radiation from stars and other Celestial Objects.

The opening up of the electro-magnetic spectrum and the other advances in technology have substantially enhanced our understanding of Celestial objects of all kinds.