cosmology

• light-year


  the distance light travels in one year
• how to calculate the distance light travels in one year

  ? x 3 x 10^8 x 60 x 60 x 24 x 365.25
• why do we use telescopes


  to observe the universe by detecting radiation from distant stars and galaxies with different detectors for various electromagnetic wavelengths
• features and limitations of optical telescopes

  - use visible light

  - have large objective lenses

  - limited by night-time and clear weather conditions
• advantages of radio telescopes

  can be used in bad weather and during daytime, detect radio waves from space
• why place telescopes in space?

  to detect electromagnetic radiation like infrared, ultraviolet, and gamma rays that are blocked by earth's atmosphere
• how do emission spectra help identify star composition

  stars emit light that forms a spectrum; matching observed spectrum lines with known element spectra can identify star composition
• estimated age of the universe and how it's determined

  13.8 billion years, determined by measuring the universe's current temperature and the rate of cooling
• cosmic radiation


  - high energy particles, mainly from supernova explosions, including protons, alpha and beta particles, and neutrinos

  - earth's magnetic field protects us from most of this radiation