Each of the five naked-eye planets, Mercury, Venus, Mars, Jupiter and Saturn, undergo substantial changes in their apparent brightness as seen from the earth during the course of each year.

The reason, of course, is that each planet constantly changes with respect to its distance from us. As the distance increases or decreases, the light we receive decreases or increases in accordance with what is known as the inverse square law of light.

If a light source is moved to double the distance, for example, the amplitude of light reaching your eyes is reduced not by a factor of two but two times two (the square of two). if a light source is moved closer, the light intensity received by your eyes is brighter by the square of the difference in distance so that a lighthouse seen from a distance of two miles is 25 times brighter than the same lighthouse seen from ten miles.

By an unusual coincidence the planets mars and Saturn now appear to be exactly the same brightness. This is a temporary condition and will not last very long.&bsp; The light from both planets is diminishing and by June 1st Saturn will outshine Mars by 10 percent, just enough to be noticed by a careful observer.

At present, both Mars and Saturn outshine all but the 12 brightest stars. Eight of these 12 are on view this month after sunset as are Mars and Saturn themselves.

Join the astronomers at FENCE, on the hill behind the FENCE&bsp; after sunset on Saturday, May 15, to see for yourself whether Mars or Saturn appears brighter, or if they look the same. They are different colors so that may affect your opinion to some degree.

In addition, on Saturday night a two-day old new moon will chaperone the brilliant planet Venus, the evening star. Venus outshines all other planets and every star as well. By seeing the moon and three planets together in one view it is easy to visualize the disc-shaped arrangement of our solar system and better understand our place in it.

We hope you will join us Saturday night for an evening of fun and adventure finding your way through the universe.

Park at the main building and walk up to the top of the hill. And dont forget to bring your binoculars!