|
Author
|
Topic: The sun's declination
|
Daniel Drapiewski
|
posted March 24, 2005 11:51 AM
I understand that the fastest rate that the sun's declination can change is 1' per hour. I don't understand why this is so. Is this simply a statement of fact (as in the statement "the earth orbits the sun once every year")? Or is there a more sophisticated explanation? Thanks for your help
|
|
David Burch
|
posted March 24, 2005 02:12 PM
This is essentially a numerical accident — rather like unitarian ministers having an average arm length of 1 meter.
If you refer to the last figure in our lecture on sun's declination (in our online course) you will see that at the solstices the dec barely changes with time at all as is crawls along the Tropics, and on the equinoxes this change is the fastest as the sun dashes across the equator, and that fastest happens to be about 1'/hour.
A bigger more prominent accident of numbers is that the much smaller moon being much closer to us happens to subtend essentially the same angle as the larger distant sun, being about 32', so that we can have a perfect eclipse with the sun almost precisely blocked by the moon in front of it.
Note that "the earth orbits the sun in one year" is more a definition of a year than a "statement of fact," if we get down to semantics as we are here.
From: Starpath, Seattle, WA
|
|
|
