s8pe-41202-ca
11/2/05
8:25 PM
VOCABULARY
Remember to put each
new term into a frame
game diagram.
reading tip
Equinox means “equal
night”—daylight and nighttime are equal in length.
Seasonal Patterns
Most locations on Earth experience seasons, patterns of temperature
changes and other weather trends over the course of a year. Near the
equator, the temperatures are almost the same year-round. Near the
poles, there are very large changes in temperatures from winter to
summer. The temperature changes occur because the amount of
sunlight at each location changes during the year. The changes in
the amount of sunlight are due to the tilt of Earth’s axis.
Look at the diagram on page 385 to see how the constant direction of
Earth’s tilted axis affects the pattern of sunlight on Earth at different
times of the year. As Earth travels around the Sun, the area of sunlight in
each hemisphere changes. At an equinox (EE-kwuh-NAHKS), sunlight
shines equally on the northern and southern hemispheres. Half of each
hemisphere is lit, and half is in darkness. As Earth moves along its orbit,
the light shifts more into one hemisphere than the other. At a solstice
(SAHL-stihs), the area of sunlight is at a maximum in one hemisphere
and a minimum in the other hemisphere. Equinoxes and solstices
happen on or around the 21st days of certain months of the year.
1
When Earth is in this position, sunlight shines
equally on the two hemispheres. You can see in the diagram that the
North Pole is at the border between light and dark. The September
equinox marks the beginning of autumn in the Northern Hemisphere and of spring in the Southern Hemisphere.
2
December Solstice
3
After another quarter of its orbit, Earth reaches
another equinox. Half of each hemisphere is lit, and the sunlight is
centered on the equator. You can see that the poles are again at the
border between day and night.
4
June Solstice
reading tip
The positions and lighting
can be hard to imagine, so
you might use a model as
well as the diagram on the
next page to help you
understand.
September Equinox
Three months later, Earth has traveled a quarter
of the way around the Sun, but its axis still points in the same
direction into space. The North Pole seems to lean away from the
direction of the Sun. The solstice occurs when the pole leans as far
away from the Sun as it will during the year. You can see that the
North Pole is in complete darkness. At the same time, the opposite
is true in the Southern Hemisphere. The South Pole seems to lean
toward the Sun and is in sunlight. It is the Southern Hemisphere’s
summer solstice and the Northern Hemisphere’s winter solstice.
March Equinox
This position is opposite the December solstice.
Earth’s axis still points in the same direction, but now the North Pole
seems to lean toward the Sun and is in sunlight. The June solstice
marks the beginning of summer in the Northern Hemisphere.
In contrast, it is the winter solstice in the Southern Hemisphere.
check your reading
384 Unit 4: Space Science
MAZER
Page 384
In what month does winter begin in the Southern Hemisphere?
PDF