If you think good sky watching only comes with deep, dark nights, look up this month. June's long hours of dusk feature magnificent sights, including an extraordinary presentation of Venus. In terms of brilliance for size, Venus is by far the most luminous object in the night sky, so bright it will no doubt inspire a flood of UFO sightings.
Because Venus circles the sun exactly 13 times for every 8 orbits Earth completes, it faithfully repeats its position and characteristics in our sky on an eight-year cycle. For example, the planet was last this brilliant in 1991, assuring us of a dazzling return this year.
Venus makes an outstanding evening star just three or four years out of every ten. And even in the good years, it's high and bright only from midwinter to late spring. During that time the planet's orbital path stretches upward, placing it far above the horizon. At other times it travels leftward from the setting sun, putting it low in the sky and forcing us to view it through the obscuring atmosphere. So next year Venus will be a bit of a dud, as it has been in the past couple of years. Sometimes finding the perfect time to view Venus demands a compromise. The planet won't shimmer its brightest until next month. But last month Venus occupied its highest perch of the year. This month the planet will be nearly at its highest and nearly at its brightest. The view will be even better because in June, Venus swings out to the edge of its orbit, far from the glare of the sun. Venus and the sun will be maximally separated, by a full 45 degrees, on June 10.
From June 12 until month's end, zippy Mercury will also climb to the edge of its orbit and stand at its best. To find it, just look for the bright light nestled between Venus and the point on the horizon where the sun sets. Mercury is not as bright as Venus, but it's worth finding because it puts in its last decent evening-sky appearance of the year.
The best way to get a face full of Venus and Mercury is to look west about 40 minutes after sunset, around 9 P.M. You'll have no trouble spotting Venus. Its creamy, steady radiance will be 60 times brighter than the brightest summer star. To the naked eye the planet is a dazzling point, and with any low-power telescope you can see a lovely half-moon shape. But remember, as you admire its beauty, that Venus's clouds of sulfuric acid, its ultrahigh air pressure, and its blistering 900-degree temperatures make it a hellhole in a rogues' gallery of unpleasant planets. (The first spacecraft to land there, Russia's Venera in 1970, was pressure-cooked into oblivion 23 minutes after touchdown.) In the coming weeks Venus will sink lower in the sky, even as it grows more brilliant. On July 15 it will form a tight triple conjunction with the crescent moon and Leo's blue star Regulus. By the end of July, Venus will vanish, not to appear again until January 2001. For the rest of the year, twilight will be starkly void of any bright stars or planets. So before the emptiness arrives, peek out the window to see Venus's last showstopping act.
