Curtain Call for the Evening Star

Venus has been a prominent evening object since last winter. But it will finally relinquish the title of "Evening Star" in less than three weeks.

Its departure will be quite dramatic.

Tonight, Venus is still fairly high up in the west-northwest sky at sunset and sets about 100 minutes later. It is now also glowing at its greatest brilliance, blazing at an eye-popping magnitude of -4.5; more than 17-times brighter than Sirius, the brightest star in the sky.

On this scale, smaller numbers represent brighter objects, and negative numbers are reserved for the brightest of all.

On the evening of Friday the 13th, Venus will pass 1.7-degrees below the bluish star Regulus, the brightest star of Leo, the Lion. (For a comparison, the apparent width of the moon is roughly equal to one-half degree.) But poor Regulus is no match for Venus, as it will appear only 1/229 as bright, so you may actually need binoculars to see this star against the twilight sky.

On Monday, July 16, you'll see a crescent moon well to the right of Venus. And hovering just above and to the right of the moon on that same evening will be the planet Saturn. The next evening, the moon will have moved well away to the upper left of Venus.

Venus will be setting about four to five minutes earlier each night, so it will be dropping noticeably lower and getting deeper into the glow of evening twilight during the waning days of July. On July 26, Venus will be setting only about an hour after sundown and by the end of July, that will have diminished to only 45 minutes; by then you'll need a clear and unobstructed horizon to spot it. A few days into August and it will be gone from our evening sky.

Curtain falls for Act I

That will mark the end of Act I for the 2007 Venus show. Then will come about a three-week "intermission," as it sweeps between the Earth and the Sun (inferior conjunction) on August 18.

Then, just a week later it will begin to emerge into view as a morning object, rising in the east about 45 minutes before sunrise. That will mark the beginning of Act II: By the end of August, Venus will be rising around 5:00 a.m. local daylight time, and ultimately will become a brilliant predawn fixture in the eastern sky for the balance of this year.

During the rest of this month, and again toward the end of August, Venus will appear as beautiful crescent in telescopes and even steadily held 7-power binoculars. That crescent will be getting progressively thinner during July, with the illuminated portion of Venus' disk diminishing from 26-percent on July 13th, to only half of that by the 27th and less than 10-percent by month's end. That crescent will also be getting progressively larger in apparent size as Venus approaches the Earth. On the 13th, it will be 41 million miles (66 million kilometers) away.

But by Aug. 1, that distance will have diminished by 11 million miles (18 million kilometers) and the filament-like crescent will appear 27-percent larger.

Parting is such sweet sorrow

For those who have been so accustomed (as I have) to seeing their brilliant friend greet them each evening at sundown in the western sky, it might actually seem a little sad to finally see Venus finally go.

But as American writer, Richard Bach once wrote: "Don't be dismayed at goodbyes, a farewell is necessary before you can meet again and meeting again, after moments or lifetimes, is certain for those who are friends."

And indeed, this will be only a temporary farewell to Venus; by the end of August her friends can meet up with her again in the eastern sky before sunrise.

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Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.