Fiery Mars, demure Spica and silvery Saturn have punctuated a prominent, drifting sort of horizontal line at dusk in the south-southwest all month.

Slowly, Mars has been moving east, narrowing its apparent distance from Spica, but the threesome has been a reliable constant. During the course of this week it will be obvious that change is afoot (or aloft). Watch each night as the configuration changes. Mars is aiming for Spica. The two will be closest in two weeks and then Mars passes Spica and heads for Saturn.

More celestial dynamism is to be enjoyed as the moon begins its waxing (increasing in size) cycle. Each evening a larger crescent appears higher in the west at dusk, paused in relationship to a different planet or star. Tonight at about 9:15, with perfect conditions -- including a clear view to the western horizon -- see an eyelash crescent setting with Jupiter to its right. Moonset will be at 9:50 p.m. Jupiter sets at 9:41. Within a few days, the giant planet disappears into the sunset glow.

Tomorrow will be less challenging: A thin crescent leads Leo the Lion toward the horizon. Leo is known by its sickle-shaped head end. Moonset will be at 10:21 p.m. The last of the latest sunsets of the year, 8:34, occurs Tuesday, when the four-day old crescent is close below Leo's brightest star, Regulus. Luna sets at 10:51 p.m., Regulus 20 minutes later. A broad crescent appears below the body of the lion on July 2 and 3.

Stay on the tour to be introduced, or reintroduced, to Mars' former close companion, Porrima, above the moon Friday. And, the piece de resistance, Saturday's half moon will squeeze between Mars and Spica, billed as one of the best conjunctions of the year.

In some locations the moon will occult, or cover, Mars.

To contact Judy Isacoff go to www.naturesturn.org