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=__Earth's Revolution and Daylight Saving Time__=

Definition:
The movement of one object (earth) around another (sun).

The earth takes 365.24 days, which is one earth year to revolve once around sun. Since the number of days to revolve around the sun is 365__.24__, we make up for the extra 0.24 by having a leap year (extra day-February 29) once every 4 years. Because of this revolution, we are in different parts of space every day for 365 days, then we return to our original spot from one year ago. Since we are in different spots, we can see different stars and planets every season that we would not see if we did not revolve around the sun. This is why we used to believe that the stars would move around in the sky, when in reality the earth was the one moving. Earth’s revolution combines with earth’s rotation to cause the seasons. Earth revolves at a speed of 29.78 kms/s, approximately 1/10,000 the speed of light. The earth’s orbit around the sun is elliptical, but very close to circular. A man named Johannes Kepler made a law called Kepler’s First Law, stating that all planets have elliptical orbits. Other planets also follow an orbit around the sun, though the orbit’s eccentricity (how elliptical it is) may be different and certainly not on the same orbit around the sun as the earth. The sun is not at the exact center of the earth’s orbit, it is a little off to the side, as shown on the picture on the right, so on January 3, also known as the Perihelion, earth is at its closest to the sun (147.5 million kms away), while on July 4, the Aphelion, earth is at its farthest from the sun (152.5 million kms away), so we are an average of 150 million kms away from the sun.

__Daylight Saving Time__
Daylight saving time is used to save the daylight during the summer. By pushing the clock forward 1 hour in the spring, you increase the sun time in the afternoon, but decrease it during the morning. Example: Say the sun goes up at 5, by pushing the clock forward in Spring now it is 6. Example: Say the sun goes down at 6, by pushing the clock forward in Spring now it is 7. Benjamin Franklin first suggested the idea of daylight saving time in his essay An Economical Project, claiming that it would save money and increase the daylight in the evening. Daylight saving time is related to earth’s revolution around the sun because its orbit combined with its rotation causes the seasons and a hot season called Summer, where people wanted to have more daylight. The idea of daylight saving time was to not "waste" the daylight because people are awake less in the morning and awake more in the afternoon. An economic benefit is that the energy saved at night when not using energy (because there is more sunlight) offsets the energy used in morning (when there is less sunlight). There are some psychological questions for daylight saving time as the change in time will cause change in sleeping habits and there is research in its effect on depression (waking up earlier), and increased heart attack risk.

http://www.uwsp.edu/geO/faculty/ritter/geog101/textbook/energy/earth_revolution_rotation.html http://www.windows.ucar.edu/tour/link=/physical_science/physics/mechanics/orbit/ellipse.html&edu=elem http://www.usatoday.com/weather/tg/wseason/wseason.htm http://www.usatoday.com/graphics/weather/gra/gseasons/frame.htm http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html http://www.webexhibits.org/daylightsaving/c.html http://www.msnucleus.org/membership/html/k-6/uc/earth/1/uce1_2a.html http://www.windows.ucar.edu/tour/link=/earth/statistics.html
 * __Sources__**