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=**Does the Earth Revolve Around the Sun? ** = Seasons, Days, and Nights Adrianna Pineda // **Season: A division of the year marked by changes in weather.** //   __Why do we have seasons?__ We have seasons because the earth rotates on a tilted axis, an imaginary line that goes straight through the north and south poles. This tilt causes the sun to be at different angles to different hemispheres throughout the year. Without it, the temperatures in the Northern and Southern hemispheres would be very similar and the sun would always be overhead the equator. Since the earth is tilted at 23.5°, the Sun’s overhead position changes throughout the year, making it appear more or less overhead in the summer or winter, respectively. In the Northern hemisphere, the summer starts when north pole moves as close to the sun as it can possibly be, and the south pole as far away, marking summer solstice. During the winter solstice, the opposite occurs. The north pole is tilted as far from the sun as it can go. As the sun moves north and south, it passes directly over the equator, marking the start of the autumnal equinox or the vernal equinox, otherwise known as autumn or spring. During the solstices, the lengths of day and night in different hemispheres have the greatest differences. The lengths of sun and darkness during the equinoxes are equal for most of the planet because the sun is directly over the equator.

To see an animation showing the Earth's movement around the sun, visit this link: []

 **Did you know?** The Earth is actually //closest// to the sun during the winter of the Northern hemisphere. The average sunlight of the entire Earth is about 7% more intense in our winter than in our summer!   __How does the Earth’s tilt affect the changes in seasons?__ When a pole is tilted the furthest distance away from the sun, the sun’s energy has to travel aurther distance to reach that hemisphere, and that the energy is spread out over a larger area, causing colder weather or winter. Summer occurs when the pole is tilted as close to the sun as possible, meaning the energy is more concentrated because there is a smaller are a to cover, and it has a shorter distance to travel. In the tropics, the change in the temperature and amount of sunlight is not noticeable, but instead, regions like Southeast Asia experience typhoon and wind cycles.

 **Did you know?** <span style="font-family: Arial,Helvetica,sans-serif;">Earth’s solar days are now slightly longer than they were in the 19th century due to tidal acceleration

__Why do we have day and night?__ Day and night is caused by the Earth’s rotation on its axis. It takes twenty-four hours for the Earth to make one rotation- one Earth day and one Earth night. The sun can only hit one side of the Earth, causing day on the side facing it and night on the side turned away. As the Earth rotates the sun’s position in the sky changes. The sun rises when the earth moves to the east. At noon, the sun is in the south because the earth is moving towards the south and then to west when the sun sets. This is why the sun rises in the east and sets in the west. <span style="font-family: Arial,Helvetica,sans-serif; text-align: left; display: block;"> <span style="font-family: Arial,Helvetica,sans-serif;"> The Earth orbits the sun every 365.25 days. On Earth, one year is equal to 365 days. However, every fourth year has an extra day added, to make up for the 0.25. <span style="font-family: Arial,Helvetica,sans-serif; text-align: left; display: block;"> <span style="font-family: Arial,Helvetica,sans-serif;">
 * Did you know?**

Sources: <span style="font-family: Arial,Helvetica,sans-serif; text-align: left; display: block;"> <span style="line-height: 200%; font-size: 11pt; font-family: Arial,Helvetica,sans-serif; text-align: left; display: block; color: rgb(0, 0, 0);">

Wilson, Tracy V. "How the Earth Works." 21 April 2006. HowStuffWorks.com. <[]> 30 May 2009

Pillai, Maya. "What Causes Day and Night." 29 May 2009 <[]>

__ What Causes Earth's Seasons? __ Ignite! Inc., 2006.

"What causes the seasons?" __Weather Questions and Answers__. 28 May 2009 <[]>.

Williams, Paige. "Scientific Reasons for Earth?s Seasons." __Breaking News, Weather, Business, Health, Entertainment, Sports, Politics, Travel, Science, Technology, Local, US & World News- msnbc.com__. 19 Mar. 2009. 29 May 2009 <[]>