If your students are tracking sunrise and sunset times, they may
have noticed these things this month:
- The
sun continues to make a comeback! We've just passed the spring
equinox (March 20), and daylength is changing more quickly.
Remember that we also moved our clocks ahead an hour for Daylight
Savings Time. So to compare apples to apples in our images from
space, we use universal time (UTC), which does not change.
-
On
the spring equinox, the length of the day and
night were about 12 hours. This was true everywhere on Earth.
(The word equinox means "equal nights.") On the equinox,
the sun's strongest rays are directly hitting the equator. The
Earth's axis is not tipped toward or away from the sun. As we
move closer to the summer solstice, students should notice that
days continue to get longer and warmer. Why? The strongest rays
of the sun begin to hit north of the equator.
Why
does all this matter?
All seasonal changes – temperature, plant growth and life
cycles, animal migrations, and so on – are driven by changes
in the amount of available sunlight (called daylength
or photoperiod) and its intensity (related to the angle
at which it strikes the Earth).