 |
|
|
|
|
|
|
|
|
|
 |
|
||||||||
 |
 |
 |
 |
 |
|
||||
 |
 |
 |
 |
 |
|
||||
 |
 |
|
|||||||
 |
|
||||||||
 |
|
||||||||
|
|
|
|
|
|
|
|
|
|
|
|
||||||||
|
|
|
|
|
|
||||
|
|
|
|
|
|
||||
|
|
|
|||||||
|
|
||||||||
|
|
||||||||
Seasons
- The Declination Panel
The Declination Panel, seen to the left, is a demonstration of how the declination
of the sun changes with the seasons. Note, the animation shows declination
above and below the celestial equator. The altitude of the sun above
the horizon at noon will be the altitude of the celestial equator plus or
minus the declination of the sun. So, how do you know the altitude of the
celestial equator? This is just 90 degrees minus your latitude.
An example. Here in Urbana, we live at a latitude of about 40 degrees north. So, on the first day of summer, the animation shows the declination of the sun is -23.5 degrees. So the suns altitude at noon is just the altitdue of the celestial equator (from Urbana, that is 90-40 = 50 degrees) minus 23.5 degrees, or 50-23.5 = 26.5 degrees. Quite low, just as we would expect for winter!
Notice that on the first day of Spring (the Vernal equinox) and the first day of Autumn (Autumnal equinox) the sun lies right on the celestial equator. Thus, its altitude at noon will just be the altitude of the celestial equator from your location (90-40=50 degrees for Urbana).
Notice too, that if we lived at a latitude of 23.5 degrees north, on the first day of summer, at noon, the sun has an altitude of 90-23.5+23.5=90 degrees -- straight overhead! For this reason, this latitude is called the Tropic if Cancer.
What would the altitude of the sun at noon be from a latitude of 23.5 degrees south (-23.5 degrees) on the first day of winter in the northern hemisphere? How about from a latitude of 63.5 north?