Im trying to get my mind around the earths tilt and its effect on
seasons, how does the tilt change from causing upper hemisphere to be
nearer the sun at one time and then 180 degrees later the lower
hemisphere is closer to the sun, isnt the tilt fixed? Also if sun is
over the equator at the equinoxes does that mean that temp is
identical in both hemispheres, how can that be that spring and
autumn(in the differnt hemisperes) is the same, that cant be?

Hi there,

The tilt doesn't change, the Earth's tilt relative to the sun changes
during the year. For half the year the northern hemisphere is leaning
toward the Sun, and for the other half the southern hemisphere is
leaning toward the Sun. Here is a diagram:
http://www.arm.gov/docs/education/lessons/images/seasons.gif

A full explanation is provided by the National Weather Service:
http://www.crh.noaa.gov/fsd/astro/season.htm

If all other factors were equal, then temperatures would be the same
at the same longitudes North or South during the equinoxes - where one
hemisphere would be in autumn, and the other in spring.

However, temperature depends on many other factors than the effects of
the Sun. You need to consider factors like trade winds, whether the
location is in the ocean or in the middle of a continent, elevation
etc...

Another explanation can be found at the Australian Bureau of Meteorology:
http://www.bom.gov.au/info/ftweather/page_4.shtml


Search strategy: I searched Google Images for "seasons", and then
visted sites that had diagrams of the Earth and Sun.


Best wishes,
robertskelton-ga

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Request for Answer Clarification by oze-ga on 13 Dec 2003 19:55 PST

Dear Robert,

Thanks for your help but I have seen all those diagrams, I still cant
understand why the tilt changes from the northern summer  the tilt is
towards the sun, if the tilt angle doesnt change as the earth orbits
the sun the tilt should remain tilted at the fixed angle and so how
can it now tilt away from the sun in the southern hemisphere summer??
Maybwe i just have a problem visualing it!!
Do you also mean to say that at the equinoxes the northern and
southern hemisphere days would have the same length at the same
longitude NOrth and South despite one being in Autumn and the other in
Spring?

Thanks for your clarification

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Clarification of Answer by robertskelton-ga on 14 Dec 2003 14:12 PST

Hi again,

Does the comment from ac67-ga help you visualize it?

Regarding your second question, yes. Regardless of it being autumn in
one hemisphere and spring in the other.

Thanks for your help

The tilt is not fixed relative to the sun.  Imagine a diagram of the
solar system on a sheet of paper, with the sun in the middle of the
sheet and the Earth's orbit around it.  Let's say in the northern
summer, the Earth is shown at the bottom of the orbit, with the
direction of tilt toward the sun. The tilt is toward the top of the
paper.  That is what stays fixed.  Half a year later, the Earth has
now moved to the top of the orbit, i.e. above the sun on the sheet of
paper.  However, the axis of tilt remains oriented toward the top of
the sheet of paper, meaning it is now away from the sun, which creates
the northern winter/southern summer.  During spring or fall, the Earth
is on either side of the paper, and the tilt remains toward the top of
the paper, neither toward or away from the sun, but perpendicular to
the line between Earth and sun.  The orientation is the same for
either fall or spring, which is why the lengths of days are the same
for the equinoxes.

Thank you so much that seems to have explained it