1. The Reasons for the Seasons Gr. 9 Science Exploration Unit

2. The planets revolve around the Sun in elliptical orbits. Each planet also rotates around its axis. Earth rotates, or makes a full turn (360  ), on its axis once every 24 hours.

3. At any given time, half of Earth experiences daylight while the other half experiences darkness. Time zones are divisions of Earth’s regions, where each regions has the same time.

4. The Earth revolves around the Sun in an orbit once each year. The tilt of the Earth’s axis affects the amount of daylight in an area. The seasons in the northern and southern hemispheres occur because the Earth remains tilted as it orbits the Sun.

5. The tilt of the Earth causes different amounts of solar energy to reach the Earth’s surface. When it is winter in the northern hemisphere, it is summer in the southern hemisphere. Other planets with tilted axes also have seasons.

6. Planets that do not have a tilted axis do not have seasons. Mercury, Venus and Jupiter fall into this category. A solstice is a day when the Earth’s axis is most inclined toward, or away from, the Sun. Equinoxes are days when the hours of daylight equal the hours of darkness.