Slideshow applet

When you see the “target rectangle with crosshairs”, click on it to wake the applet up. Zoomed in, the iMicro projects a 383 × 223 rectangle. Aim it at the target rectangle. Then press and (down and up arrow) to cycle forward and backward through the following slides and movies. If the applet doesn’t respond to the arrows, reload the page, click on the applet, and try the arrows again.

The drawing displayed by the applet has a 10-pixel margin on each side, so it is 400 × 243. Each of the six captions is 400 × 20.

Java source code of the applet. To open the Java Console on MacOSX, search for “Plugin Settings” and check “Show Java Console”. Applications → Utilities → Restricted


  1. The Solar System is not like a 1950’s picture of an atom. In the atom, the orbits of the electrons are pitched every way.
  2. In the Solar System, the orbits of the planets lie in the same plane.
  3. Why did it take so long to discover that the planets orbiting the sun? If we could view it from above, we would see the planets circling the sun. But our earth is always in the plane, so we see the Solar System edge-on. All we see are the planets going back and forth. The moon and sun also lie along the same line. (Show Zeiss Ecliptic and Zodiac.)
  4. Mars is currently in retrograde motion. View from the sun: Mars moves at constant speed, pointer moves at constant speed.
  5. View from a stationary Earth: Mars still moves at constant speed, but pointer speeds up whenever we go past Mars (at 3 o’clock).
  6. View from a moving Earth: Mars still moves at constant speed, but pointer goes backwards whenever we go past Mars (at 3 o’clock).
  7. We see the galaxy edge-on, just like the Solar System.
  8. Each arm is a logarithmic spiral. The pitch angle is a constant 12°.
    r = abθ
    θ = logb (r/a)
    tan 12° = ln b
  9. Logarithmic spiral is path that hawk follows to prey: keeps prey at same visual angle. A hawk does not see most clearly in the direction it’'s flying. Insects keep the sun at a constant bearing to fly in a straight line. They will also keep a nearby source of light at a constant bearing, causing them to spiral inwards.
  10. A simple model of how the arms of a galaxy form. The stars follow elliptical orbits, and the orbits are oriented differently as they get bigger. The individual stars move in and out of the arms; the arms are merely areas of heavy traffic.
  11. An arm is not made of permanently connected stars: the stars move in and out of the arm. A simple model of how the arms could have a permanent existance hile the stars move through them, like rubberneckers on the New York State Throughway.
  12. The “B” in “Betelgeuse” is a misreading of the Arabic letter “Y”.