Last summer I was fiddling around with Starry Night Pro, using the software to preview planet configurations that will be taking place later this spring. Upon focusing my attention on Saturn and skewing quickly through the month of March, I was taken by surprise by a dot that seemed to whiz past the great ringed beauty during the middle of the month.

I quickly had the program back up a few days, then moved forward in time again, but this time, much more slowly.

Sure enough, the dot reappeared, and as I gradually moved past March 19th, I watched with amazement as it skimmed very close to Saturn, at one point almost touching it.

Here, I said to myself, will be an excellent opportunity for anyone to positively identify an asteroid. Usually to spot one visually, you would need a telescope and a very good sky chart with the asteroids position correctly plotted. Identification can still be uncertain unless you can readily detect some slight motion over a short span of time. Otherwise, to the eye, asteroids look like stars (hence the word asteroid, Greek, for "like a star").

Yet, on Tuesday evening, March 19, Saturn will serve as a guide for telescopic observers with a rare opportunity to identify one of the solar systems largest asteroids.

On that night, Vesta will appear to pass within about 3 minutes of arc of Saturn for viewers across North America. To get a rough idea of how large in real terms that is, the apparent width of the Moon is, on average, 30 minutes of arc. So Vesta will be passing roughly one-tenth of a Moons width from Saturn.

Another way to look at this is to know that the apparent width of Saturns rings, visible in a small telescope, measures approximately 3/4-minute of arc. So the gap between Vesta and Saturn should appear equal to about four ring widths.

Through a telescope, Vesta will appear as a tiny "star" of magnitude +8.3, not visible to the naked eye. It will be off to south and east of Saturn. Note that many telescopes invert the image you see. In a telescopes that inverts the image, Vesta will be below and to Saturn's right. In a non-inverting telescope, Vesta will be above and to the left of Saturn.

Make sure not to confuse Vesta with the brightest satellites of Saturn (Titan, Rhea, Dione, Tethys, Iapetus and Enceladus) all of, which will be noticeably fainter and noticeably closer to Saturn.

An interesting postscript to this story: On the small chance that I might have been the first to discover this unusual circumstance involving Saturn and Vesta, I phoned, Roger Sinnott, a Senior Editor of Sky & Telescope magazine. I was brought back to Earth when Sinnott told me that some months prior to my "Starry Night discovery," Jean Meeus, a specialist in spherical and mathematical astronomy, had also informed him of the impending Saturn/Vesta configuration.

According to Meeus, Vesta will make its closest apparent approach to Saturn on March 19th at 10:48 a.m. EST (during daylight across North America).

At that moment, Saturn and Vesta will be separated by a mere 1.8 arc minutes, or about 1/17th the apparent width of the Moon. Vesta will be 253 million miles from Earth, while Saturn will be 867 million miles away. Yet, by sheer coincidence, both objects will appear to almost exactly line-up in space from our perspective here on Earth.