What
Scientists Think
-
Did
you notice that temperatures seem to get cooler as you go
north or south from the equator?
-
Did
the temperature bands seem to move north in the first half
of the year and south in the second half of the year?
Here's
why:
Because
the earth is tilted on its axis, the sun heats it unevenly.
Areas closest to the equator (tropical and
subtropical zones) get more direct sunlight
all year. They are the hottest zones. Areas farther from the
equator (temperate and polar
zones) get less direct sunlight, and the number of
hours of sunlight per day changes a great deal throughout the
year.) They are colder regions.
During
our summer, the Northern Hemisphere leans toward the
sun in its revolution. There are more daylight hours, and the
sun’s angle is more direct than at other times of year.
So it's warmer. The opposite happens in the winter
when we are tilted away from the sun. Its rays are slanted (less
intense) and we have fewer daylight hours.
As
we move from summer to fall and winter (as the earth revolves
and is eventually tipped away), days get shorter and the temperatures
get cooler. The opposite happens from winter to summer.
But the Southern Hemisphere is tilted away
from the sun when we are tilted toward it. So they
have opposite seasons and temperature patterns. That's why the
temperature lines on the map seem to move north and south with
the seasons.
These
global temperature differences cause our different climates
(including factors such as winds, humidity, and precipitation)!
Journaling
Questions
- How
do you think temperature changes over the course of a year
affect the animal you're studying and its migration? How
do they affect your animal's ability to meet its basic needs?
- Do
you think everyone throughout the United States and Canada
experiences four seasons? If you have friends and family
in other parts of the country, ask about their seasons.
How different is each one? Once you've thought about this,
read the box below.
Seasons
in the United States and Canada?
Seasons are often defined as the major divisions of the
year that are based on temperature and/or precipitation
changes. In parts of the South, the average temperatures
may only change from 75 degrees in the winter to 90 degrees
in the summer. But to someone from the Midwest, where average
temperatures could range from -20 in the winter to 80 in
the summer, the Southern seasons hardly count! In general,
places farther to the south and closer to water have smaller
seasonal variations. It's a matter of opinion and just might
depend on how you define "seasons." |