Seasons
By the Lunar and Planetary Institute
For use in teacher workshops
What do your students think causes the seasons?
http://nix.ksc.nasa.gov/info
December
True color images
March
June September
http://www.nasa.gov/vision/earth/features/blue_marble.html
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
http://www.lpi.usra.edu/education/skytellers/seasons/about.shtml
Northern Hemisphere Summer
More daylight hours, more direct sunlight
http://www.lpi.usra.edu/education/skytellers/seasons/about.shtml
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
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.
Daylight Hours Across the Globe
Time is indicated as number of hours (h)
Miami Brisbane Nairobi Punta Arenas Nome Singapore Cape Town Seattle Vostok
Jan Feb 10.5 h 11 h 14.5 h 12 h
Mar 12 h
Apr 12.5 h
May 13 h 11 h 12 h 10 h
Jun 14 h 11 h 12 h 8.5 h
Jul Aug 14.5 h 14 h 11 h 12 h 8.5 h 22 h 12 h 10.5 h 16.5 h 0h 11.5 h 12 h 9.5 h 18 h 12 h 11 h 15.5 h 0h
Sep 12.5 h 11.5 h 12 h 11.5 h 15.5 h 12 h 11.5 h 13.5 h 7h
Oct 12.5 h 12.5 h 12 h 13 h 11.5 h 12 h 12.5 h 11.5 h 15 h
Nov 11 h 14 h 12 h 15 h 8.5 h 12 h 14 h 10.5 h 24 h
Dec 11.5 h 14.5 h 12 h 16.5 h 5.5 h 12 h 14 h 9.5 h 24 h
13.5 h 13.5 h 12.5 h 12 h 12 h 12 h
17.5 h 15.5 h 5h 12 h 15 h 9h 24 h 7h 12 h 14 h 10 h 24 h
13.5 h 11.5 h 10 h 12 h 13.5 h 12 h
17.5 h 21.5 h 13 h 13 h
13.5 h 12.5 h 11 h 19 h 13.5 h 14.5 h
11.5 h 10 h 15 h 0h 17 h 0h
http://www.lpi.usra.edu/education/skytellers/seasons/activities/light.shtml
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!
Seasons on Planets
Planet Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Axial Tilt 0° 177° 23° 25° 3° 27° 98° 30° Eccent. 0.21 0.01 0.02 0.09 0.05 0.06 0.05 0.01 Orbit 88 days 224 days 365 days 686 days 12 years 30 years 84 years 165 years Perihelion 28 mill. Miles Aphelion 43 mill. miles
91 mill. miles 94 mill. miles 129 mill. miles 155 mill. miles
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