The Properties of Stars

We can determine an amazing number of physical properties of stars, usually based only on a little bit of light. Over the next several lectures, ``we'' will talk about how the following properties are determined for stars.

  1. BRIGHTNESS. This is not a fundamental property, but a combination of the luminosity and distance to a star (and in some cases also dependent on the amount of absorption in the direction of a star).

  2. DISTANCE. From trigonometric and spectroscopic parallaxes. Determining distances to stars is how we figure out the scale of things in the Galaxy and is CRUCIAL to understanding stars because we can use the inverse square law for light dimming along with apparent brightness of stars to figure out how much energy is being produced and radiated away.

  3. LUMINOSITY. This is the amount of energy generated in the star and released as electromagnetic radiation.

  4. RADIUS tex2html_wrap_inline274 ``Size''. From Stephan's Law.

  5. CHEMICAL COMPOSITION. From the absorption line spectra. This one is tied up in a semi-complicated way with the next one.

  6. TEMPERATURE. We have talked about Wien's Law and using colors to derive stellar temperatures, but, there are some complications. To REALLY get to surface temperatures of stars, we need to learn about and understand stellar Spectral Types.

The Bigger Picture

  • First - let's get oriented. We live out in the suburbs of a pretty good sized spiral galaxy that contains on the order of tex2html_wrap_inline276 stars.


    What are the stellar Constellations?

    Just people connecting dots. Many of the stars that are close together in the plane of the sky (the projection of the three dimensional galaxy into two dimensions) are quite far apart long the line of sight.


    What about star names?

    The brightest stars have various names - mostly from long ago. There are no ``official'' names for stars. The often used convention in the West is to use the Greek alphabet to identify the brightest stars belonging to some constellation.

    Stellar Brightness

    Michael Bolte
    Mon Jan 26 12:32:25 PST 1998