ASTRON 1101 Lecture Notes - Lecture 31: Thomas Digges, Heinrich Wilhelm Matthias Olbers, Angular Diameter
15 Nov 2016
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The darkness of the night sky isn"t caused by dark matter . Dark matter might be better named invisible matter ; it doesn"t emit, or absorb, or scatter light. This sentence is olbers" paradox, named after the german astronomer heinrich wilhelm. Why is the darkness of the night sky paradoxical: if stars were actually stuck to a celestial sphere, the darkness wouldn"t be paradoxical, a few thousand stars on the sphere produce just a small amount of light. The paradox arose in the 16th century, when thomas digges spoke of innumerable stars in infinite space. The basic unit of length will be the megaparsec (mpc) 1 mpc = 106 parsecs = (cid:885). (cid:884)6 (cid:883)(cid:882)6 lightyears = (cid:885). (cid:883) (cid:883)(cid:882)22 meters: 33% more than the distance from here to the andromeda galaxy. Suppose there are n stars per cubic megaparsec: from censuses of galaxies, n = 109 stars/mpc3. Suppose an average star has a luminosity l.
