Astronomy is primarily an observational science. It is driven
more by new observational discoveries than by interpretive insights.
Few important astronomical discoveries were predicted, and many were
actually accidental. The human imagination has never been a match
for the universe.
Astronomical discovery began with the simplest of observations: people
looking at the night sky and trying to understand what they were
seeing. In the past, most people were well acquainted with the basic
features of the night sky. Today, most are unfamiliar with the sky
mainly because of the advent of artificial lighting, which makes it
difficult to see the night sky in urban areas (and also unnecessary to
know the sky as a pathfinder).
This lecture introduces you to the basic features of the night sky which
are visible to the unaided eye and prepares you for the Constellation
The diurnal motion: The daily spin of the Earth on
its axis produces an apparent counter-rotation of the CS and its
"attached" stars across your local sky. One complete rotation around
its axis with respect to the stars takes 23h56m. The Earth
rotates eastward, so the sky appears to rotate continuously
westward. Objects "rise" in the east or "set" in the west when
they cross your local horizon plane. See the figure above.
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Last modified September 2008 by rwoText copyright © 1998-2008 Robert W. O'Connell. All rights reserved. Opening fisheye lens picture of comet Hale-Bopp and night sky from Ujue, Spain, April 1997, copyright © J. C. Casado. Illustrations of the celestial sphere copyright © by Nick Strobel. Image of M13 copyright © by J. Ware. These notes are intended for the private, noncommercial use of students enrolled in Astronomy 1230 at the University of Virginia.