seasons what do your students think causes the seasons? by the lunar and planetary institute for...
TRANSCRIPT
Seasons
What do your students think causes the seasons?
http://nix.ksc.nasa.gov/info
By the Lunar and Planetary Institute
For use in teacher workshops
04/21/23 The Seasons 2
Rotation vs. Revolution
• Rotation is the spin of an object about its axis.– The Earth rotates once a day (once every 24
hours).• Revolution is the orbit of one object around
another.– The Earth revolves around the Sun every
365.26 days.
Solar Heating
The sun or any light, heats a surface mosteffectively when it is shining directly onto
the surface.
04/21/23 The Seasons 4
Day Night Cycle
True color images
June
December March
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
04/21/23 The Seasons 7
More daylight hours, more direct sunlight
Northern Hemisphere Summer
http://www.lpi.usra.edu/education/skytellers/seasons/about.shtml
Seasons vs. hemispheres
• Northern and southern hemisphere have reversed seasons.
Seasons
In summer, the sun is at a smaller angle,more effective heating.
In winter, the sun is at a larger angle, lesseffective heating.
04/21/23 The Seasons 14
Seasons Misconception
• Many people carry the misconception that the seasons are due to the distance of the Earth from the Sun. However, consider the following facts:– The Earth’s orbit around the Sun is nearly a
perfect circle. The Earth is slightly closer to the Sun in January and farther from the Sun in July.
• Perihelion (closest to the Sun) is around January 3 when Earth is about 91,405,436 miles from the Sun.
• Aphelion (farthest from the Sun) is around July 4 when Earth is about 94,511,989 miles from the Sun.
04/21/23 The Seasons 15
Seasons Misconception
– While it is winter in the Northern hemisphere it is summer in the Southern hemisphere. If the seasons were due to our distance from the Sun both hemispheres would have the same seasons at the same time.
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
Equinox
• Sun rises due east• Sun sets due west• Exactly 12 hours of day, 12 hours of night• Once in spring• Once in fall• When the sun is directly over the equator.
Solstice
• Summer solstice:• Longest daylight off the year• Sun at noon is highest in the sky
• Winter solstice:• Shortest daylight off the year• Sun at noon is lowest in the sky
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
Seasons DiagramThe seasons are cyclical. They occur in
order: Winter, Spring, Summer, Fall (Autumn).