Seasons reviewBill Nye! (4 min)

Outline Notes:

Big Idea:

The seasons are the result of:1) the tilt of the Earth's axis, and2) revolution around the sun

•If the tilt of the Earth's axis was 0°there would be no difference in how the rays from the sun hit its different regions (there would be no seasons)

Equinoxes and Solstices

Quick reminder!Label on your page now!

What is a solstice?

• either the shortest day of the year (winter solstice)or the longest day of the year (summer solstice)

Make a quick T chart in your notes – title it “Solstice”

Winter Solstice Summer Solstice

Winter Solstice• During the December Solstice the Sun’s rays shine on the Tropic of

Capricorn.

• Happens on or around December 21st (the tilt is 23.5S)

• At the December solstice, the Northern Hemisphere is leaning the most away from the sun for the year.

• All locations south of the equator have day lengths greater than 12 hours at the December solstice.

• Meanwhile, all locations north of the equator have day lengths less than 12 hours.

• For us on the northern part of Earth, the shortest day comes at this solstice. After the winter solstice, the days get longer, and the nights shorter.

Winter Solstice• Stonehenge is carefully aligned on a sight-line that points to the winter solstice sunset. This

Stonehenge monument – built in 3,000 to 2,000 BC – shows how carefully our ancestors watched the sun. Stonehenge is perhaps the most famous of the ancient astronomical monuments found around the world.

Winter Solstice

• The northern hemisphere is pointed furthest away from the sun • The sun is directly over the Tropic of Capricorn• The shortest day of the year in the northern hemisphere

Summer Solstice

• During the June Solstice the rays of the Sun shine directly on the Tropic of Cancer.

• Happens on or around June 21st (the tilt is 23.5N)

• At the June solstice, the Northern Hemisphere is leaning most toward the sun for the year.

• All locations north of the equator have day lengths greater than 12 hours at the June solstice.

• Meanwhile, all locations south of the equator have day lengths shorter than 12 hours.

• For us on the northern part of Earth, the longest day comes at this solstice. After the summer solstice, the days get shorter, and the nights longer.

Summer Solstice at Stonehenge

Summer Solstice

• The northern hemisphere is pointed furthest toward the sun • The sun is directly over the Tropic of Cancer• The longest day of the year in the northern hemisphere

Summer solstice in the artic

• The sun never sets!

So an equinox is…?• Equinox: the date (twice each year) at which the sun crosses the equator, therefore day and night are of equal length (about September 22 and March 20).

Equinox (means – Equal night )

Equinoxes are halfway between the solstices, neither hemisphere is tilted toward or away from the sun

The noon sun is directly overhead at the equator

There are 2 equinoxes, the vernal and autumnal - these classical names are direct derivatives of Latin (ver = spring and autumnus = autumn)

Video: National Geographic (3 min)

Make another quick T chart in your notes – “Equinoxes”

Spring (Vernal)Equinox Fall Equinox

Spring and Fall Equinox• Vernal (spring) and autumnal (fall) equinox - the

sun is directly over the equator

• Days and nights are equal in length

Vernal (Spring) Equinox

• March 21st

• Marks the beginning of spring in the northern hemisphere

• The March equinox marks the moment the Sun crosses the celestial equator – the imaginary line in the sky above the Earth’s equator –from south to north

Celestial Sphere• As people first started to map out the

night sky, it became necessary to have a standard, way of plotting objects in the sky.

• As the stars appear to occupy fixed positions in the sky relative to each other, a convenient way of thinking about the situation would be to imagine the Earth placed at the center of a larger sphere.

• The stars occupy fixed positions on the surface of this 'celestial sphere', and the Earth rotates within it.

• This is obviously not the case in real life but it is a good model because this is pretty much how things look from our point of view.

Celestial Equator

Autumnal Equinox

• September 23rd

• Marks the beginning of fall in the northern hemisphere

• The September equinox marks the moment the Sun crosses the celestial equator –the imaginary line in the sky above the Earth’s equator –from north to south

Equinoxes and Solstices

Video for review

•Summary video -http://www.tamingdata.com/2010/12/21/the-winter-solstice-explained-science-version/

What to do now:

Daylight Map:

Activity help: