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View Full Version : Can someone explain seasons to me?

EnderW25
2002-Jan-03, 05:46 AM
We have four seasons which occur as we hover between 91 and 93 million miles from the sun. The only difference between Winter & Summer and Fall & Spring seems to be the angle of the Earth as compared to the sun. Why is this such a significant factor? Why is the fact that we're 2 million miles closer to a gigantic ball of fire not really that large of an issue when determining temperature?

Wally
2002-Jan-03, 11:04 AM
The difference in our distance from the sun over the course of a year doesn't amount to much from a percentage standpoint (only a 1 to 1.5 percent change from furthest to closest, I believe). The main factor controlling our seasons is whether your particular locale is gaining more heat during daylight than it can lose during nightime. So, while tilted towards the sun, a hemisphere not only receives sunlight more directly, but also for a longer period of time per day. Both account for the net gain in heat over the course of a 24 hour period, which eventually leads to spring, then summer. For my location, I believe this net gain actually starts sometime in late January, approx. 1 month after the shortest day of the year (the winter solstice). Hope this helps.

GrapesOfWrath
2002-Jan-03, 11:16 AM
The eccentricity of Earth's orbit is 1.67 percent, but with a semimajor axis of 93 million miles, that would mean its distance from the Sun would vary between 94.5 and 91.5 million miles. If you were to take a square piece of cardboard and move it from 91.5 million miles away from the Sun to 94.5 million miles, the amount of sunlight falling on it would decrease to about (91.5/94.5)^2 (.938) of what it was in the first place. That's about a 6 percent decrease.

If you were to take the same piece of cardboard and tilt it away from the Sun at a 45 degree angle, the amount of sunlight falling on it decreases to the cosine of 45 degrees (.707) of what it was. That's a 29 percent decrease. Right now, every place in the United States is tilted at more than 45 degrees, relative to the Sun at noon (OK, not Honolulu--but it's warm there!). That's why the tilt is so more important than the distance from the Sun.

And the days are shorter, as Wally says.

<font size=-1>[Added ecc. info, and nod to Wally]</font>

<font size=-1>[ This Message was edited by: GrapesOfWrath on 2002-01-03 07:07 ]</font>

Wiley
2002-Jan-03, 04:39 PM
Well, you see, it's like this ...

One day Proserpine, daughter of Ceres, was playing in the fields with her friends when Pluto, lord of the underworld, espied her. Instantly smitten, Pluto carried her off to the underworld to ... well, to do those things lords usually do in the underworld. Needless to say, Ceres, upon discovering her daughter missing, was grief stricken. She searched Earth for her daughter, but Proserpine was not to be found. But in her search she neglected her duties as goddess of agriculture, and winter took the land.

Eventually Ceres learned the truth of her daughter's abduction from the river nymph Arethusa. Thus spake Arethusa, "blame not the land; it opened unwillingly to yield a passage to your daughter. I can tell you of her fate, for I have seen her." Holding no sway in the underworld, Ceres went to Jupiter for redress.

Jupiter told Ceres that she could have Proserpine back, but only if she had not eaten during her stay. Alas, Proserpine had eaten a pomegranate Pluto had offered, and this was enough to prevent her release. However a compromise was made: Proserpine would spend half the year with Ceres and the other half in the underworld with her now husband Pluto. While Proserpine is with Pluto, Ceres pines for daughter and neglects the land.

And this why we have seasons.

A more detailed version can be found here (http://www.bulfinch.org/fables/bull7.html).

ToSeek
2002-Jan-03, 07:45 PM
On 2002-01-03 11:39, Wiley wrote:

Jupiter told Ceres that she could have Proserpine back, but only if she had not eaten during her stay. Alas, Proserpine had eaten a pomegranate Pluto had offered, and this was enough to prevent her release. However a compromise was made: Proserpine would spend half the year with Ceres and the other half in the underworld with her now husband Pluto. While Proserpine is with Pluto, Ceres pines for daughter and neglects the land.

The variant I've usually heard is that Proserpine had eaten six pomegranate seeds and so has to stay in the underworld for six months - the same number of months as the number of seeds.

In any case, thanks for the strict factual explanation. /phpBB/images/smiles/icon_wink.gif

<font size=-1>[ This Message was edited by: ToSeek on 2002-01-03 14:46 ]</font>

EnderW25
2002-Jan-04, 12:25 AM
Wow, I was going to thank GrapesOfWrath for the very informative mathematical explanation. Then I read Wiley's post and realized that GoW had it completely wrong. Thank you for setting the record straight.

GrapesOfWrath
2002-Jan-04, 10:32 AM
I bow to Wiley's superior intellect. Shoulda waited until after he posted. Next time, I'll know better.

ToSeek
2002-Jan-04, 02:39 PM
On 2002-01-03 19:25, EnderW25 wrote:
Wow, I was going to thank GrapesOfWrath for the very informative mathematical explanation. Then I read Wiley's post and realized that GoW had it completely wrong. Thank you for setting the record straight.

Oh, and the Sun goes around the Earth because Phoebus drives it around in his big chariot. Just so you know. /phpBB/images/smiles/icon_wink.gif