Equinox and Solstice
What are they and why are they
important to us?
• Earth rotates (spins) on its axis at a tilt of 23.5 degrees which
remains constant throughout the year. It takes 24 hours to make a
whole rotation (purple arrows).
• Earth revolves (goes around) the sun. It takes 365 days to make a
whole revolution (red arrows).
The Earth is…
Revolving around the sun
But, the Earth is also…
Rotating on its axis
What do you already know…
about seasons on Earth?
How sunlight hits the earth depends,
in part, on latitude.
Seasons are caused by Earth’s tilt
and
Earth’s revolution around the sun.
Seasons are NOT caused by
earth’s distance from the sun.
What do you already know…
about equinoxes?
The “equinox” occurs twice a year
when the sun is directly overhead
at the equator.
On the equinox, the hours of daylight
equals the hours of darkness.
Seasons in the northern & southern
hemispheres are opposite.
6
Equinoxes
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There are two days in the year when the day and night are exactly equal in
both the northern and southern hemisphere. They occur September 21 and
March 21 (or about). We call those fall equinox and spring equinox.
Every one in the world experiences 12 hours of daylight and 12 hours of night.8
What do you already know…
about solstices?
The “solstice” is the day of the
year when sunlight is furthest
north or south of the equator.
Our summer solstice occurs on June
21st, the first day of summer.
Our winter solstice occurs on
December 21st, the first day of winter.
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Northern Summer Solstice
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Southern Summer Solstice
Notice how being tilted on an axis makes the northern hemisphere of the Earth get more
sun than the southern during the months of July, August and September—we call that
summer. The days are longer and the nights are shorter, creating a warmer temperature
for that time. In the southern hemisphere, it is winter. The longest day of the year in
the north is June 21—we call it the summer solstice.
The north pole gets 24 hours of daylight and the south pole gets 0 hours of daylight
during our summer solstice.
Notice how being tilted on an axis makes the northern hemisphere of the Earth get less
sun than the southern during the months of January, February, and March—we call that
winter in the northern hemisphere. The nights are longer and the days are shorter,
creating a colder temperature for that time. In the southern hemisphere, it is summer.
The shortest day of the year in the north is December 21—we call it the winter solstice.
The south pole gets 24 hours of daylight and the north pole gets 0 hours of dayligh
during our winter solstice.
Because of the 23.5° tilt of Earth’s axis, the altitude of the sun varies cyclically
across a year. In winter it’s 23.5° below the celestial equator, while in summer it’s
23.5° above. At the equinoxes, it straddles the equator. From the equator, the
celestial equator passes directly overhead, at mid-latitudes, we see it halfway up
in the sky, while at the poles it circles 360-degrees around the horizon. Created
with Stellarium
Oliver Nagy made this cool
image between the June
and December solstices in
2014. The camera was fixed
to a single spot for the
entire exposure time, and it
continuously recorded the
sun’s path as glowing trail s
across the sky. The breaks
and gaps between the lines
are caused by clouds. This
image shows the shifting
path of the sun over the
months between a June
and December solstice. As
seen from the Northern
Hemisphere, the sun’s path
gets lower each day.
It is the tilt of the Earth that causes the seasons. Without it, we would have
consistent temperatures all year. This impacts our weather, climate, ability to grow
crops, live in certain areas, and enjoy the activities in each of the seasons.
Watch this simulation:
Geography seasons
Some people think that on the days of the equinox, you should be able
to balance an egg on its end. What do you think?
World record, egg balancing—1290 eggs!
(not all pictured)