Unit 1 Lesson 3: Time and Seasons

Unit 1 Lesson 3

Time and Seasons

The Rotation Axis

The rotation axis of Earth is an imaginary line that runs through Earth from the north pole to the south pole

This axis is NOT perpendicular to its orbit around the Sun, but is instead tilted 23.5 degrees from vertical

This means that the Earth is always receiving sunlight at a slight angle

Uneven Sun

•  Because Earth maintains its tilt on its path around the Sun, sunlight falls more directly on the Northern hemisphere for part of the year and more directly on the southern hemisphere for another part of the year

• This changes the amount of heat and the length of sunlight we receive over the course of a year

Multiple Choice

What Causes the Seasons?

• The Earth is closer to the Sun in the summer

• The Sun is brighter in the summer

• The Earth's tilt means we get more sunlight in the summer

• Global Warming

The Movement of the Sun

• Because of the tilt of the Earth, the sun's path through the sky changes position

• Around June 21st the North pole is pointed as close as possible towards the sun

• Around December 21st the South pole is as close as possible towards the sun

The sun changes position in the sky based on the season

Equinoxes

• The sun crosses the celestial equator twice each year. When the sun is on the celestial equator the days and nights are of equal length so the dates are called an equinox: "equal night"

• The vernal (spring) equinox happens near March 20

• The autumnal (fall) equinox is near September 22

Solstices

• The beginning of summer and winter mark the times when the sun pauses in its north-south motion and changes direction; these are the solstices (sol for sun and static for stop)

• Summer Solstice: Around June 21st

• Winter Solstice: Around December 21st

Multiple Choice

Which of the following dates marks the beginning of Spring?

• Vernal Equinox

• Summer Solstice

• Autumnal Equinox

• Winter Solstice

Multiple Choice

Which of the following dates marks the End of Summer?

• Vernal Equinox

• Summer Solstice

• Autumnal Equinox

• Winter Solstice

Multiple Select

On which of the following dates will the days be longer than the nights?

• Summer Solstice

• Fall Equinox

• Winter Solstice

• Spring Equinox

Multiple Select

On which of the following dates will the length of the day be the same as the length of the nights?

• Summer Solstice

• Fall Equinox

• Winter Solstice

• Spring Equinox

Tracking the Sun's Changing Position

• The motion of the sun north and south in the sky over the course of the year causes the sun to follow different path through the sky each day as the Earth rotates

• For a northern observer the Sun is high in the sky at noon on a summer day but low in the sky at noon on a winter day

• Where the Sun is located in the sky is measured in relation to the horizon or the zenith, the point in the sky straight overhead

Multiple Choice

On which of the following dates will the sun be the lowest in the sky at Noon?

• Summer Solstice

• Fall Equinox

• Winter Solstice

• Spring Equinox

• Because the Sun moves north and south of the celestial equator it rarely rises and sets due east and due west

• On the vernal (spring) equinox it rises and sets due east and due west

• From the vernal equinox to the summer solstice it shifts northward each day

• From the summer solstice to the winter solstice it shifts southward each day, hitting due east and due west again at the autumnal equinox

• After the winter solstice it begins moving north again

Multiple Select

Which of the following statements are true?

• On the equinoxes the sun rises from due East

• After the spring equinox, the sun starts shifting further and further north

• At the summer solstice, the sun stops moving north and starts moving south again

• At the winter solstice, the sun is as far south as it will go in the sky

• The path the sun follows each day can be quite different at different latitudes

• North Pole: Sun remains above the horizon for half the year

• Equator: Sun is up for 12 hours every day of the year, reaches its highest point at the equinoxes, not the solstices, sun’s path is about perpendicular to the horizon so the sun rises and sets very quickly

Poll

Which would you prefer? To live where the days are always 12 hours long or to live where there are months at a time that the sun never sets?

• Equal-length days, please!

• 6 months of sun for me!

The sun’s rising and setting positions on the horizon change each day as the Sun travels north and south. This was used as an indicator of the seasons.

Stonehenge was built to take advantage of where the rising and setting sun were during different time frames

Some Egyptian temples and pyramids have astronomical alignments