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.
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.
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