Thursday, March 29, 2007

Venus Visits Star Sisters

Venus visits star sisters
by Dave Adalian

If you go out tonight around 8:30 p.m. and look west you’ll find white Venus shining brilliantly back at you from above the horizon.

Venus will be about 20 degrees high or four times the width of your fist held at arm’s length with knuckles raised and thumb tucked. Not quite that same distance above Venus you’ll discover a cluster of blue-white stars in the shape of a tiny dipper. They are the Pleiades, or Seven Sisters, and they’re on course for a close pass with Venus that will be a stargazer’s delight.

Of course their apparent proximity will be just an illusion. Venus is never farther than 160 million miles from Earth, while the Seven Sisters are some 400 light years away.

And there are a lot more than just seven sisters. Most folks see just six of the Pleiades with their naked eyes. Viewing with binoculars drives the number much higher, and a telescope reveals 100 or so suns blazing away in a cluster that fills a spherical area 14 light years across.

The much smaller but brighter Venus is a dainty 8,000 miles wide, just a deep breath thinner than its twin Earth.

While these celestial ladies look to be a fair distance apart at the moment, over the next couple of weeks they’ll pull together until they’re a scant 2.5 degrees separate, close enough an extended hand could hide them.

It just so happens Venus will seem to stand almost perfectly still with respect to the Sun over the next few weeks, so most of the effect we’ll be witnessing is the stars shifting as the days of spring pass and Earth races through its orbit at some 67,000 miles an hour.

The change will be subtle at first. It takes until Tuesday for the Pleiades to close to within 10 degrees of Venus, but then the pace picks up and the distance will be 5 degrees by Saturday, April 7, and only 4 degrees the next night.

The gap shrinks about half a degree a night until Venus and the Seven Sisters reach their closest on Wednesday, April 11. The two will still be a mere 2.75 degrees apart the next night and only 3 degrees distant the night after that.

Venus will still be just 10 degrees above the Seven Sisters on Thursday, April 19, when a thin slice of crescent moon settles between them.


This column originally appeared in the Visalia (Calif.) Times-Delta and Tulare (Calif.) Advance-Register on March 29, 2007.

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