FRED ESPENAK / SCIENCE PHOTO LIBRARY FRED ESPENAK / SCIENCE PHOTO LIBRARY
Ultraviolet spectrum of the quasar 3C 273 taken in the wavelength between 1200-1400 Angstrom. The red dotted line represents the centre of the spectrum with the wavelengths superimposed. The white spot next to 1200 Angstrom is hydrogen's Lyman-alpha line at its usual wavelength while the spot near 1400 Angstrom represents the same emission as we receive from the quasar. The difference between the two wavelengths is explained as a Doppler effect due to the expansion of the universe. According to Hubble's law of expansion, this shift puts the quasar at 2100 million light years away from the Earth.
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