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The Question
(Submitted February 11, 1998)
How does the earth's tilt affect the changing of the seasons,
and what different angles cause those different seasons?
The Answer
The bottom line for the changes from season to season is the average
daytime temperature. This depends on the amount of heating that the
earth receives in a single day throughout the year, and this depends
on how many hours the Sun is above the horizon and exactly how long it
spends at its highest elevation above the horizon. For every square
meter on the surface of the earth, it will be heated by the Sun at a
rate that depends on the 'cosine' of the angle of the Sun above the
horizon. The higher the Sun gets, the less slanted the rays of light
are that intercept each square meter, and so the efficiency with which
these slanted rays can deliver energy to the surface gets better and
better the higher up the Sun gets. When you add up during the daylight
hours just how much heating this surface gets, it receives most of its
heating from those times during the day when the Sun is the highest
above the horizon. For a tilted earth, there will be some days during
the year at a given latitude, where this heating rate is the highest
and we call this summer. There will be other days when the Sun never
gets very high above the horizon and so its heating ability is very
low, and we call this winter. The details of just how hot and cold we
get, and the exact dates, depend also on whether we are near water, or
in the interior of a continent.
So, seasonal changes depend on the tilt of the earth's axis because
they lead to changes in the amount of heat delivered to a square meter
of surface, and the fact that there are a changing number of hours in
the day when the Sun is above the horizon and high enough up that it
can efficiently heat the surface over the course of a typical day.
(from
Ask a Space Scientist)
There is an activity on our StarChild website that illustrates
how the earth's tilt affects the change in the seasons. Take a look at
http://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level2/javascript/song.html
Jim Lochner and Maggie Masetti
for Ask an Astrophysicist
Questions on this topic are no longer responded to by the "Ask an Astrophysicist" service. See http://imagine.gsfc.nasa.gov/docs/ask_astro/ask_an_astronomer.html
for help on other astronomy Q&A services.
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