Emission Spectra and Spectral Analysis of Stars

Light and Spectra

• • When light passes through a prism or diffraction grating, it splits into its component colors (wavelengths), forming a spectrum.
  • There are three main types of spectra:
    
    • Continuous Spectrum: Produced by a hot, dense object (like a filament). Shows all colors without gaps.
    • Emission Spectrum: Bright lines on a dark background; produced by hot, low-density gas emitting specific wavelengths.
    • Absorption Spectrum: Dark lines on a continuous background; occurs when cooler gas absorbs specific wavelengths from a hot source behind it.

Emission Spectra of Stars

• • Each element emits light at specific wavelengths → characteristic lines called spectral lines.
  • By observing a star’s emission spectrum, scientists can identify the elements present in the star’s atmosphere.
  • Example: Hydrogen produces the Balmer series; Sodium produces yellow lines.

Spectral Classification

• • Stars are classified by the absorption lines in their spectra, which relate to temperature and composition.
  • Main spectral types: O, B, A, F, G, K, M (O = hottest, M = coolest).
  • Example: The Sun is a G-type star; Sirius is an A-type star.

Doppler Effect in Spectral Lines

• • If a star moves away, its spectral lines are redshifted (longer wavelength).
  • If a star moves toward Earth, its lines are blueshifted (shorter wavelength).
  • This allows astronomers to measure the star’s radial velocity and the expansion of the universe.

Importance of Spectral Analysis

• • Determines chemical composition, temperature, density, mass, and motion of stars.
  • Helps to classify stars, understand stellar evolution, and study galaxies.