Light Scattering Demonstration The jar in the images below contains water to which one drop of fresh homogenized milk has been added, and the contents have been stirred. The physics of using milk in this experiment are based on its homogenization. Most of the milk globules are within an order of magnitude of about one micron in size, just right for a dramatic illustration of forward-scattered light. That's because this range of small size particles, somewhat larger than the wavelength of light, results in pronounced scattering in the forward direction (see references below). Caution: milk that has not been refrigerated will foul the experiment, because as it begins to curdle, and the size of the suspended globules begins to vary from the optimal size. Backscatter Forward Scatter ABOVE: An observer standing on the same side as the laser, looking at the light beam entering the glass, sees a spot of backscattered light on the glass itself. Beyond the glass, the beam shows relatively little backscatter as it goes through the dilute milk suspension. ABOVE: Standing on the other side of the jar, looking back toward the laser (visible in the background), one can see that there is a relatively large amount of forward scattering. Scattering changes only the direction of light. Mirrors do that, too, but scattering is not simple reflection, which changes the direction of a beam without making it broader. Scattering is a re-distribution in all directions of the incoming light. Download the excellent NASA Educational Brief (pdf) for which this page offers some partial illustration. View this Cassini image of Saturn's rings backlit by the Sun. Notice the brightness of the dusty Cassini Division, and the inner C Ring due to the forward scattering of sunlight. Most of the B Ring appears dark because it is dense enough to block much of the sunlight from coming through from behind. Here's the backlit Saturn showing all the tiny particles in the E Ring, the G Ring, the F Ring, the Cassini Division, etc. References: NASA Educational Brief (PDF) Sky color and scattering of light Omega Engineering discussion Examples at Saturn Dave's Baiscs of Interplanetary Flight, a Public Programs course at Art Center College of Design Page updated UTC 22 September 2009 / dd