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Name: Loli. A
Status: Educator
Age: 30s
Location: N/A
Country: N/A
Date: December 10, 2002


Question:
How do you visualize or show the seasons if the earth's tilt changed -say 90degrees? I am trying to visualize this myself and am stumped - maybe because it seems catastrophic!



Replies:
If the tilt of the earth were to change from its current 23¢ to 90¢ would be catastrophic to all life on earth. This question has been asked and answered on another board:

http://im agine.gsfc.nasa.gov/docs/ask_astro/answers/980211f.html

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_lev el2/javascript/song.html

Jim Lochner and Maggie Masetti
for Ask a High-Energy Astronomer
Questions on this topic are no longer responded to by the "Ask a High-Energy Astronomer" service. See

http:// imagine.gsfc.nasa.gov/docs/ask_astro/ask_an_astronomer.html for help on other astronomy Q&A services.

Steve Miller


The easiest way to visualize is to picture (or use a model of) the geometry of sun and earth, and pick a point on earth for different orientations of the axis and locations of the earth in its orbit around the sun.

In the extreme case, imagine the case where the earth's axis was in the same plane as the earth's orbit. Once a year, the north pole would directly face the sun, and 6 months later, the south pole would directly face the sun. At those times, the sun would stay almost exactly in the same spot for the whole day for someone at the pole, and people in the> northern or southern hemisphere would see the sun travel in a circle at the same height over the horizon.

The effect on season would be most extreme at the poles- when facing the sun, that pole of earth would get direct sun continuously, about equal to being on the equator, but having no nighttime to cool off. When facing away from the sun, it would be similar to winters in the arctic or antarctic circle, a continuous night.

It would be catastrophic for life as we know it. But not to fear, the type of event that could change the axis that severely would be so catastrophic that the change in seasons would be the least of our concerns. If the earth had always had this different axis tilt, life on earth would be very different, depending on where you lived.

Don Yee


Loli -

Catastrophic would be the word for it. It is hard to guess what would develop if the earth were to spin directly on its side. One of the other planets - Uranus - does move like this. Because its year is 84 earth years long, a point on Uranus has about 42 years of daylight and 42 years of night. For the earth that would be about 180 of our present days for one "on-the-side" day. It would likely mean the end of life on earth as we know it.

The earth is actually changing its inclination to the sun, but it is very slight. We say it is 23.5 degrees and that is pretty close. There was a theory about 50 years ago that the earth would tip periodically and suddenly to assume a new axis of rotation... but the new axis would be inclined roughly 90 degrees. I have heard nothing of this theory for many years. That is likely for failing under scientific scrutiny.

Larry Krengel


Well, it WOULD make the weather quite unpleasant. Just as now, the poles would be in light for half the year and darkness for the other half. However, the intensity of the sunlight would vary much more dramatically than it does now. At the solstice, the pole near the sun would experience the direct overhead rays of the sun, as the tropics do now.

The rest of the planet would be both tropical and arctic; tropical because the sun would appear to the north and to the south at different times of the year, and arctic because the extreme periods of the year would involve continuous sunlight and continuous darkness, respectively. At two times during the year, the sun would be directly overhead. So the temperature differences between summer and winter would be dramatic. Every place would receive intense sunlight when the sun is overhead.

The most consistent location to be would be at the equator. Things would be odd even here. Only here would there be both day and night every day of the year. Day and night would be of equal length throughout the year, as it is now. At the equinoxes, the sun would be directly overhead. At the two solstices, the sun would be just at the horizon all day long, both day and night.

The best way to visualize this is with a globe. You'll have to take it out of its stand, because globe stands typically are fixed at the natural angle of the earth's tilt. Place the globe so that its polar axis is horizontal to the ground, and place a light source at the same height as the globe. The light shining on the globe will then model the sunlight illuminating the earth. As the earth rotates about its polar axis and revolves around the sun, you can see how the day/night pattern in various locations depends on the time of year.

Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois



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