SeasonsWhat do you think causes the seasons?

Images at http://nix.ksc.nasa.gov/info

Created with help from by the Lunar and Planetary Institute

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Werner - • During the day, the earth is heated by the sun. If skies

are clear, more heat reaches the earth's surface (as in the diagram below). This leads to warmer temperatures.

•However, if skies are cloudy, some of the sun's rays are reflected off the cloud droplets back into space. Therefore, less of the sun's energy is able to reach the earth's surface, which causes the earth to heat up more slowly. This leads to cooler temperatures.

•Forecast Tip: When forecasting daytime temperatures, if cloudy skies are expected, forecast lower temperatures than you would predict if clear skies were expected.

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• At night cloud cover has the opposite effect. If skies are clear, heat emitted from the earth's surface freely escapes into space, resulting in colder temperatures.

•However, if clouds are present, some of the heat emitted from the earth's surface is trapped by the clouds and reemitted back towards the earth. As a result, temperatures decrease more slowly than if the skies were clear.

•Forecast Tip: When forecasting nighttime temperatures, if cloudy skies are expected, forecast warmer temperatures than you would predict if clear skies were expected.

Ava -

• Solar variation is the change in the amount of radiation emitted by the Sun and in its spectral distribution over years to millennia

Raul -

Fernando –

• Position of the equinoxes, solstices, aphelion, and perihelion relative to the Earth's orbit around the Sun.

Shakira -

• Rotation and Revolution: The Earth completes one revolution (or orbit) around the sun every year (365 days). The Earth completes one rotation on its axis every 24 hours.  Day and night are caused by the Earth's rotation on its axis.

While in June the northern hemisphere is tilted toward the sun the Earth is actually farther away from the sun.

Susan

Let’s Look at Some Data!

• Temperatures around the World• Daylight hours

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

 

  January April July October

Cape Town (South Africa) 69 66 60 65

Caracas (Venezuela) 75 81 78 79

London (United Kingdom) 44 56 73 58

Mexico City (Mexico) 66 77 73 70

Montreal (Canada) 22 51 79 56

Moscow (Russia) 21 47 76 46

Nairobi (Kenya) 77 75 69 77

Paris (France) 42 60 76 59

San José (Costa Rica) 75 79 77 77

Seoul (Korea) 33 62 84 67

Singapore 86 89 87 88

Stockholm (Sweden) 31 45 70 48

Sydney (Australia) 79 73 62 72

Tokyo (Japan) 48 64 84 70

True color images

June

December March

September

Images at http://www.nasa.gov/vision/earth/features/blue_marble.html

Animation-Earth’s Life through Seasons

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

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.

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.

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

More daylight hours, more direct sunlight

Northern Hemisphere Summer

Image at 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

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

Seasons on Planets

Planet Axial Tilt Eccent. Orbit Perihelion Aphelion

Mercury 0° 0.21 88 days 28 mill. Miles 43 mill. milesVenus 177° 0.01 224 daysEarth 23° 0.02 365 days 91 mill. miles 94

mill. milesMars 25° 0.09 686 days 129 mill. miles 155

mill. milesJupiter 3° 0.05 12 yearsSaturn 27° 0.06 30 yearsUranus 98° 0.05 84 yearsNeptune 30° 0.01 165 years

Mars’ Orbit and Seasons

At summer solstice, Mars is 153 million miles from the Sun

At autumnal equinox, Mars is 134 million miles from the Sun

At winter solstice, Mars is 128 million miles from the Sun

At vernal equinox, Mars is 145 million miles from the Sun

Original images from http://photojournal.jpl.nasa.gov/index.html