Seasons

1. Seasons What do your students think causes the seasons? Images at http://nix.ksc.nasa.gov/info Created by the Lunar and Planetary Institute For Educational Use Only LPI is not responsible for the ways in which this powerpoint may be used or altered.

2. Let’s start with a couple “probes” Snowball!

3. Let’s Look at Some Data! • Temperatures around the World

4. Average Daily Temperatures (°F) in Tourist Cities (from http://www.infoplease.com/ipa/A0004587.html ))

5. Let’s Start with some Observations • Using free downloaded computer program, Stellarium: http://www.stellarium.org/ • Stellarium is planetarium software that shows exactly what you see when you look up at the stars. It's easy to use, and free. • Let’s look at sunrise & sunset, and Sun’s height in the sky.

6. True color images December March June September Images at http://www.nasa.gov/vision/earth/features/blue_marble.html

7. Animation-Earth’s Life through Seasons

8. Modeling the Seasons Time to grab a styrofoam ball and a light!

9. Height of Sun for USA Winter: The Sun rises in the southeast, stays low in the sky, and sets in the southwest. Spring: The Sun rises due east, moves higher in the sky than in winter, and sets due west. Summer: The Sun rises in the northeast, travels high (near zenith), and sets in the northwest. Fall: The Sun rises due east, travels to a medium-height in the sky, and sets due west.

10. What Causes Earth’s Seasons? • Earth’s axis is tilted 23.5 degrees – it always points in the same direction (Polaris, the North Star) as we orbit our Sun once a year • This tilt causes the hemispheres to alternate in the amount of our Sun’s light and heat they receive through the year Image at http://www.lpi.usra.edu/education/skytellers/seasons/about.shtml

11. Northern Hemisphere Summer More daylight hours, more direct sunlight Image at http://www.lpi.usra.edu/education/skytellers/seasons/about.shtml

12. Earth’s orbit is almost a perfect circle • Earth is CLOSEST to our Sun (91 million miles) in winter—January 3 • Earth is farthest from on our Sun (94 million miles) in summer –July 4

13. Daylight Hours Across the GlobeTime is indicated as number of hours (h) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 10.5 h 11 h 12 h 12.5 h 13 h 14 h 14.5 h 14 h 12.5 h 12.5 h 11 h 11.5 h 14.5 h 13.5 h 13.5 h 12.5 h 11 h 11 h 11 h 11.5 h 11.5 h 12.5 h 14 h 14.5 h 12 h 12 h 12 h 12 h 12 h 12 h 12 h 12 h 12 h 12 h 12 h 12 h 17.5 h 15.5 h 13.5 h 11.5 h 10 h 8.5 h 8.5 h 9.5 h 11.5 h 13 h 15 h 16.5 h 5 h 7 h 10 h 13.5 h 17.5 h 21.5 h 22 h 18 h 15.5 h 11.5 h 8.5 h 5.5 h 12 h 12 h 12 h 12 h 13 h 13 h 12 h 12 h 12 h 12 h 12 h 12 h 15 h 14 h 13.5 h 12.5 h 11.5 h 10 h 10.5 h 11 h 11.5 h 12.5 h 14 h 14 h 9 h 10 h 11 h 13.5 h 15 h 17 h 16.5 h 15.5 h 13.5 h 11.5 h 10.5 h 9.5 h 24 h 24 h 19 h 14.5 h 0 h 0 h 0 h 0 h 7 h 15 h 24 h 24 h Miami Brisbane Nairobi Punta Arenas Nome Singapore Cape Town Seattle Vostok http://www.lpi.usra.edu/education/skytellers/seasons/activities/light.shtml

14. Seasons on Other Planets • In some cases, the changing distances from the Sun will affect the seasons. • In others, the axial tilt will make a huge difference! Image at http://photojournal.jpl.nasa.gov/catalog/PIA01589 Image at http://photojournal.jpl.nasa.gov/catalog/PIA02963

15. Seasons on Planets PlanetAxial Tilt Eccent. Orbit Perihelion Aphelion Mercury 0° 0.21 88 days 28 mill. Miles 43 mill. miles Venus 177° 0.01 224 days Earth 23° 0.02 365 days 91 mill. miles 94 mill. miles Mars 25° 0.09 686 days 129 mill. miles 155 mill. miles Jupiter 3° 0.05 12 years Saturn 27° 0.06 30 years Uranus 98° 0.05 84 years Neptune 30° 0.01 165 years

16. Mars’ Orbit and Seasons At vernal equinox, Mars is 145 million miles from the Sun At winter solstice, Mars is 128 million miles from the Sun At summer solstice, Mars is 153 million miles from the Sun At autumnal equinox, Mars is 134 million miles from the Sun Original images from http://photojournal.jpl.nasa.gov/index.html

17. An Assessment • Best procedures: read quietly to yourself (so you don’t give any subconscious clues) • As the instructor, we read it too, for timing, then ask if anyone needs more time • If not, it’s time to vote simultaneously—use your fingers, right in front of your chest so others don’t see (anonymous) Northerners have cold days in January because • the Earth is farthest from the Sun in January. • the sunlight takes a longer route to get to the Earth in January. • the Sun is lower in the sky in January. • El Nino is always strongest in January.

18. Another Which of the following statements help explain why summer days tend to be hotter than winter days? In that region, • The day is longer. • The Earth’s surface receives more light per unit area. • The light is coming more directly from the Sun. • There is no snow to cool the Earth. • Just a • Just c • a and d • a and c • b and c

19. What would the days and seasons be like in Houston if the Earth still rotated at the same speed, but the Earth’s axis were tilted nearly 50 degrees on its side instead of 23 degrees? • Both days and seasons would be half a year long. • The days would be the same length, but the seasons would be half a year long. • There would be no seasons, but days would be 6 months long. • The days and seasons would be the same lengths as ours, but the seasons would have more extreme temperature changes.