Temperature:
* Blackbody Radiation: Stars emit radiation across a wide range of wavelengths, following the laws of blackbody radiation. The peak of this radiation is directly related to the star's surface temperature.
* Spectral Class: By analyzing the spectral lines (absorption and emission lines) in a star's spectrum, astronomers can classify the star into a spectral class (O, B, A, F, G, K, M). Each spectral class corresponds to a specific temperature range.
* Color Index: Measuring the brightness of a star through different color filters (e.g., blue, green, red) provides a color index. The color index is directly related to the star's temperature.
Composition:
* Spectral Lines: The presence, intensity, and position of specific spectral lines in a star's spectrum reveal the chemical elements present in the star's atmosphere. Different elements absorb and emit light at specific wavelengths, creating unique "fingerprints" in the spectrum.
* Line Strengths: The strength of spectral lines (how dark or bright they are) indicates the abundance of the corresponding element.
* Doppler Shift: Measuring the shift in the wavelengths of spectral lines due to the star's motion (radial velocity) can also provide information about the composition, as certain elements are more susceptible to shifts caused by the star's magnetic field.
In summary, these are the key characteristics scientists measure:
* Light Spectrum: The distribution of wavelengths in the light emitted by the star.
* Brightness: The amount of light received from the star.
* Color: The apparent color of the star based on its spectral distribution.
* Radial Velocity: The speed at which the star is moving towards or away from us.
By analyzing these characteristics, scientists can effectively deduce the temperature and composition of distant stars, providing valuable insights into their physical properties, evolution, and the composition of the universe.
