Saturday, September 20, 2008

A picture is worth a thousand words

Steve, who left a comment on yesterday’s post, suggested that lots of pictures would be better than Wikipedia’s prose. I agree.

At this website, created by someone in the Physics Department of Durham University in the United Kingdom, some of the diagrams even move.

The first diagram illustrates that the sun would always be directly above the equator if Earth’s axis were not tilted. The second diagram, which unfortunately is stationary, shows that Earth’s axis is tilted off vertical by 23.5 degrees (something we are all supposed to have learned when we were ten). The third diagram illustrates what I was trying to say, and saying so poorly, in yesterday’s post.

The northernmost point on Earth that receives the direct rays of the sun at midday (that is, the sun is directly overhead at midday and the rays are perpendicular to the surface of Earth) is called the Tropic of Cancer. The southernmost point on Earth that receives the direct rays of the sun at midday is called the Tropic of Capricorn. If you live north of the Tropic of Cancer or south of the Tropic of Capricorn, the sun is never directly overhead.

If you want to know more, you’ll have to find out for yourself.

This topic may not be exhausted, but I am.


  1. First, it was hexadecimals; then leap seconds; now it's elipses!

    Actually, the animated graphs were pretty interesting. :)

  2. Not elipses, Pat, and not eclipses, either, but the ecliptic! A different animal altogether.

    I will try to stay away from scientific subjects from now on, because I am in way over my head. But I do enjoy astronomy.

  3. I suppose years ago I learned the significance of the tropics of cancer and capricorn, but I haven't thought of them for a long time. Why is it that the sun seems to be straight up overhead in the summer, even though we're way north of the tropic of cancer? Its an illusion, probably.

  4. LOL... I stand corrected! (muttering to self: e.c.l.i.p.t.i.c.)

  5. OK I think I am beginning to see the light.