Page 174 - Science Course 3 (Book 2)

Mo12-L2b: Why Do the Seasons Change?

Northern hemisphere Same amount of sunlight
receives more sunlight as on southern
hemisphere

Same amount of sunlight
Southern hemisphere as on northern
receives less sunlight hemisphere

June Solstice March Equinox
The June solstice is on June 20th or 21st. The March equinox is on March 20th or 21st.
On this day On this day

• the north end of Earth’s rotation axis is toward • the north end of Earth’s rotation axis leans along
the Sun; Earth’s orbit;

• days in the northern hemisphere are longest and • there are about 12 hours of daylight and 12 hours
nights are shortest, summer begins; of darkness everywhere on Earth;

• days in the southern hemisphere are shortest and • spring begins in the northern hemisphere;
nights are longest; winter begins.
• autumn begins in the southern hemisphere.

An equinox is a day when Earth’s rotation axis is The Sun’s apparent path through the sky in the
leaning along Earth’s orbit, neither toward nor away northern hemisphere is lowest on the December
from the Sun. solstice and highest on the June solstice.

Same amount of sunlight
as on southern
hemisphere

Same amount of sunlight
as on northern
hemisphere
December Solstice March Equinox

September Equinox
The September equinox is on September 22nd or
23rd
On this day

• the north end of Earth’s rotation axis leans along
Earth’s orbit;

• there are about 12 hours of daylight and 12 hours June Solstice September Equinox
of darkness everywhere on Earth;

• autumn begins in the northern hemisphere;
SUMMARY
• spring begins in the southern hemisphere.
Why Do the Seasons Change?

Equinoxes and solstices are days when the
direction of Earth’s rotation axis relative to the
Sun is special.

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