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Updated June 07, 2022
  parallax

Image: The annual parallax is used to estimate the distance of a star. Scientists measure the parallax angle by noting the position of a star on the celestial vault, at 6 month intervals. To do this, just take measuring from a position of the Earth in its orbit, and measuring again 6 months later when the Earth is on the other side of the Sun. The diameter of the Earth's orbit is ≈300 million km, the parallax angle gives the distance by a simple trigonometric calculation.

nota: A parallax of 1 second corresponds to a distance of 3.26 light-years. This unit of length is called the parsec (PARallaxe SEConde)
    
  Standard candles

Image: Cepheids whose luminosity is known become "standard candles" to measure the distance of distant stars and that of nearby galaxies. The intrinsic luminosity of classical Cepheids increases with their blinking period. Credit NASA

    
  cigar galaxy supernova or M82

Image: Supernova SN 2014J in the Cigar Galaxy (M82). The explosion of the star is shown by the arrow, in the right part of this galaxy remarkable for its bright blue disc. Bright Supernova in M82 Image Credit: Adam Block, Mt. Lemmon SkyCenter, U. Arizona.

    
  redshift

Image: Absorption spectral lines in the optical spectrum of a distant supercluster of galaxies (upper panel) compared to a nearby object, the Sun (lower panel). Arrows indicate redshift or increase in lower energy wavelengths. Credit: Georg Wiora

 
           
           
   
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