MadSci Network: Astronomy
Query:

Re: Length of the day and earths rotation

Date: Mon Jul 27 11:20:33 1998
Posted By: Mike Francis, Other (pls. specify below), Physics/Astronomy, Self employed/ Amazing Discoveries Productions
Area of science: Astronomy
ID: 901365180.As
Message:

Lee,

You have indeed missed some key points. Your clock measures mean solar time. A mean solar day is the time it would take a mean sun to appear to move from the meridian back to the meridain one time, 24 hours. You may say "The Sun isn't mean, it gives us light and heat." In this case we are talking about an average Sun, that appears to move along the celestial equator at a constant rate. Our Sun appears to move along the celestial equator because, as you stated, the Earth orbits the Sun every 365.2442 days. The Earth's orbit is not a perfect circle though, it is an elipse. If you've studied Keplar you know that when the Earth is closest to the Sun it moves more quickly than when it is at its furthest. Telling time with the Sun constantly appearing to move at a different rate could pose a tricky problem. To simplify things, astronomers have defined the mean solar day to correct for the different lengths of the day due to the Earth's position relative to the Sun. Thus our definition of a day is already corrected for the motion of the Earth around the Sun.


Current Queue | Current Queue for Astronomy | Astronomy archives

Try the links in the MadSci Library for more information on Astronomy.



MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci


MadSci Network, webadmin@www.madsci.org
© 1995-1998. All rights reserved.