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WEATHER
Seasons
Seasons
- The earth orbits around the sun once in a year. This orbit is nearly a circle. (It is actually just a little bit elliptical, but othat's not a factor in our seasons. Note that the importance of the changing distance to the sun is a major MISCONCEPTION. We are actually closer to the sun during our winter and Australia's summer.)
- The earth also spins on its axis once in 24 hours.
- This imaginary axis is tilted with respect to the plane of the earth's orbit. This means that at certain times of the year, the northern hemisphere is tilted towards the sun, and at certain times of the year we are tilted away. (When we are tilted towards the sun, the folks in Australia are tilted away and vice versa.)
- The tilt has two important effects:
1. When we are tilted towards the sun, the sunlight is more direct. From earth, the sun appears more overhead. At noon during this time of the year, shadows are shortest. The sun's light is less "spread out" and thus more intense.
2. When we are tilted towards the sun, we spend more of our daily rotation in sunlight. Days are longer. We get more hours of the more intense sun. - In the northern hemisphere, our longest day of most intense sun is the summer solstice, approximately June 21st. Our shortest day of least intense sun is the winter solstice, approximately December 21st. In between these dates we have the spring equinox (~March 21) and the fall equinox (~September 21) where our tilt is neither towards nor away from the sun and everyone on earth gets 12 hours of sunlight. The seasons follow these dates (i.e. summer comes AFTER the most intense sun and longest day) because it takes the earth time to heat up and cool down.
- Seasons simluator: http://astro.unl.edu/classaction/animations/coordsmotion/eclipticsimulator.html
- Explanation of Seasons simulator from Jeff:
Sun
- The sun is our nearest star. Its light, traveling at 186,000 miles a second, takes 8 minutes to get to us.
- Shadows will move over the course of the day as the earth spins and the sun appears to move from east to west.
- The direction of the earth's spin is counter-clockwise as viewed from above the north pole.
- A suspended magnet will always point it's north pole north because it's really called a "north-seeking pole" on the magnet, and it is attracted to the pole of the earth's magnet.