Seasons are divisions of the year marked by distinct weather patterns, changes in temperature, and variations in daylight hours. They are primarily determined by the Earth's axial tilt and its orbit around the Sun. The four main seasons recognized in many regions of the world are spring, summer, autumn (fall), and winter. Here's a brief description of each season: 1. Spring: Spring is the season that follows winter and precedes summer. It is characterized by gradually increasing temperatures, longer daylight hours, and the emergence of new plant growth. In many places, spring is associated with blooming flowers, budding trees, and the return of various animal species. 2. Summer: Summer is the warmest season of the year. It is marked by higher temperatures, extended daylight hours, and generally favorable weather conditions. Summer is often associated with vacations, outdoor activities, and the opportunity to enjoy beaches, swimming, picnics, and various recreational pursuits. 3. Autumn (Fall): Autumn, also known as fall, is the season that follows summer and precedes winter. It is characterized by cooler temperatures, shorter daylight hours, and the shedding of leaves from deciduous trees. Autumn is often associated with vibrant foliage, harvest festivals, and a gradual transition towards colder weather. 4. Winter: Winter is the coldest season of the year. It is marked by low temperatures, shorter daylight hours, and, in many regions, the presence of snow and ice. Winter is often associated with holidays such as Christmas and New Year's, as well as activities like skiing, snowboarding, ice skating, and cozy indoor pursuits. It's important to note that the timing and characteristics of seasons can vary depending on the geographical location, as well as regional climatic conditions.

1. Why do we
have
seasons?

2. Earth’s rotation
• The Earth rotates on its axis
(imaginary vertical line
around which Earth spins)
every 23 hours & 56
minutes.
• One day on Earth is one
rotation of the Earth.
• Day on Earth is when our
side of the Earth faces the
sun.
• Night on Earth is when the
side of Earth we are on
faces away from the sun.
CLICK ON THIS IMAGE
TO VIEW A SHORT VIDEO
OF THE EARTH’S ORBIT

3. Earth’s revolution
• It takes the Earth ~365.25days (or rotations) to
travel or revolve around the Sun once.
• This is called a year.

4. Why do we have seasons?
• The Earth’s orbit around
the sun is NOT a perfect
circle. It is an ellipse.
• Seasons are not caused
by how close the Earth is
to the sun.
• In fact, the Earth is
closest to the sun around
January 3 and farthest
away from the sun
around July 4.

5. Why do we have seasons?
• Seasons are the result of the
tilt of the Earth's axis.
• Earth’s axis is tilted 23.5°.
• This tilting is why we have
SEASONS like fall, winter,
spring, summer.
• The number of daylight
hours is greater for the
hemisphere, or half of Earth,
that is tilted toward the Sun.

6. Why do we have seasons?
• Summer is warmer than winter (in each
hemisphere) because the Sun's rays hit the
Earth at a more direct angle during summer than
during winter

7. Why do we have seasons?
• Also the days are much longer than the nights
during the summer.
• During the winter, the Sun's rays hit the Earth at an
extreme angle, and the days are very short. These
effects are due to the tilt of the Earth's axis.

8. Seasons…in a nut shell

9. Solstices
• Solstices occur twice a year, when the tilt of the Earth's
axis is oriented directly towards or away from the Sun,
causing the Sun to appear to reach its northernmost and
southernmost extremes.
• Winter solstice is the shortest day of the year. In the
Northern Hemisphere. It occurs on December 21 and
marks the beginning of winter.
• The Summer Solstice is the longest day of the year. It
occurs on June 21 and marks the beginning of summer.
Tyrrhenian Sea and Solstice Sky
Credit & Copyright: Danilo Pivato

10. SOLSTICE
• During the winter the Northern Hemisphere day lasts fewer than
12 hours and the Southern Hemisphere day lasts more than 12
hours.
• During the winter solstice, the North Pole has a 24-hour night
and the South Pole has a 24-hour day.
• Sunlight strikes the earth most directly at the Tropic of
Capricorn.
C.LICK ON THE
ANIMATION
FOR A SHORT VIDEO ON
SOLSTICES FROM
NATIONAL GEOGRAPHIC

11. Notice that the Sun’s angle is greater in the summer
and is higher in the sky, and it has a lower angle and
it is lower in the winter sky.
SUN’S ANGLE DURING SOLSTICES

12. Equinoxes
• A day lasts 12 hours and a night lasts 12 hours at all
latitudes.
• Equinox literally means "equal night".
• Sunlight strikes the earth most directly at the equator.
• This occurs twice a year.
C.LICK ON THE ANIMATION
FOR A SHORT VIDEO ON
EQUINOXES FROM
NATIONAL GEOGRAPHIC

13. Equinox
• The vernal (spring)
equinox occurs usually
March 20th.
• The autumnal (fall)
equinox occurs
• usually September
22nd.

14. The Earth's seasons are not
caused by the differences in the
distance from the Sun throughout
the year.

15. The seasons are the result of
the tilt of the Earth's axis.
I know this is a repeat, but it is important that you understand
this idea. Many Americans, including Harvard graduates,
do not know what causes seasons!

16. Review
Look closely at where the Sun is hitting the
Earth during each season:
https://www.learner.org/jnorth/tm/mclass/sl/6/index.html

17. http://www.nmm.ac.uk/uploads/gif/seasons-full.gif
When does the Earth(in the northern
hemisphere) receive the greatest amount
of direct energy from the sun? When does
it receive the least amount of energy?