Since the end of January,
the planet Venus has been on sort of a winter and early spring sabbatical. It
passed superior conjunction (appearing to go behind the Sun as seen from Earth)
back on March 30. Since then, it has been invisible, mired deep in the brilliant
glare of the Sun.
But with each passing day,
Venus has been moving on a slow course toward the east and pulling away from
the Sun's general vicinity.
Finally, during early May,
it has begun to emerge as an evening "star" very low in the western
twilight. On the evening of May 13, it sets 27 degrees north
of due west (10 degrees is roughly equal to the width of your fist held at arm's
length) nearly an hour after sunset.
By June 1 this will have
improved to 80 minutes, giving even casual observers their first view of the
famed "Evening Star." It's so bright that it can be spotted even through
twilight very low in the west-northwest 45 minutes after sunset, so look early,
preferably with binoculars.
Appearing as a brilliant
white star-like object, our sister planet will adorn the western evening sky
through the remainder of this year.
Poor summer viewing
Unfortunately, for most
Northern Hemisphere observers this is going to turn out to be a rather crummy
evening apparition of Venus, especially during the summer months. The reason
for this lies in Venus' placement in the sky relative to the Sun; from June
19 through December 8 Venus' will appear to have a more southerly declination
than the Sun.
As a consequence, it will
appear unusually low to the horizon right after sunset, especially through most
of this summer.
On July 1, for example,
for those living at or near 40 degrees north latitude, will see Venus set just
1½ hours after sunset. At mid-twilight, it will appear to hover only about 6
degrees above the horizon. By August 31, this situation will have not improved
much at all, as Venus will still be setting only 1½ hours after sundown and
at mid-twilight will stand only about 8 degrees above the horizon. This also
means that at no time through July and August will Venus be visible against
a completely dark sky, as it will set before the end of evening twilight.
(In contrast to these poor
viewing conditions, Skywatchers in the Southern Hemisphere will see Venus pull
well away from the Sun and gradually soar progressively higher in the evening
sky during July and August. By the end of August, in fact, Venus will be setting
more than 3 hours after the Sun and will appear more than 20 degrees above the
horizon by the end of evening twilight).
Better in autumn
During September and October,
however, the view will begin to slowly improve for northern observers for three
reasons:
1) Venus will be
getting brighter as it rounds the Sun and speeds toward Earth.
2) Twilight fades
faster in the fall than in summer, leaving Venus to shine in a darker sky; by
mid-September, Venus finally sets just after the sky has become completely dark.
3) Venus will shift
over from the west to the southwest. Objects at a given altitude above the horizon
in the southern part of the sky take longer to set than objects at the same
altitude due west, so the difference between the setting times of the Sun and
Venus will ever so slowly increase. On Oct. 1 Venus will be setting 1¾ hours
after the Sun, but this improves noticeably to nearly 2½ hours by Halloween.
Venus reaches its greatest
elongation - its greatest angular distance - 47 degrees to the east of the Sun
on Nov. 3. It is brightest in early December as it heads back down toward the
Sun, reaching its greatest brilliancy for this apparition on Dec. 9 at a dazzling
magnitude of -4.5 (smaller numbers are brighter on this scale,
and negative numbers are the brightest).
By then it will be an eye-catching
sight in the southwest sky for at least a couple of hours after sunset right
on through the Christmas season. Venus then quickly fades, vanishing from view
in early January 2006, and passes inferior conjunction on Jan. 13. Within a
week it reemerges as a morning "star" in the southeast.
Between now and early January,
repeated observation of Venus with a small telescope will show the complete
range of its phases and disk sizes.
The planet is now virtually
full (98-percent sunlit on May 13), and appears as a tiny, dazzling disk. It
will become noticeably less gibbous by late summer. In early November, Venus
reaches dichotomy (displaying a "half moon" shape). Then, for the
rest of the year it displays a large crescent as it swings near the Earth. Indeed,
those using telescopes will note that while the Earth-Venus distance is lessening,
the apparent size of Venus' disk will grow, doubling from its present size by
Oct. 11.
When it has doubled again
in size on Dec. 7, its large crescent shape should be easily discernable even
in steadily held 7-power binoculars.
Basic Sky Guides
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Astronomy
for the
Entire Family!
Starry
Night software brings the universe to your desktop. Map the sky from
your location, or just sit back and let the cosmos come to you.
LEARN
MORE!
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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.
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DEFINITIONS
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Degrees
measure apparent sizes of objects or distances in the sky, as seen from
our vantage point. The Moon is one-half degree in width. The width of
your fist held at arm's length is about 10 degrees.
Magnitude
is the standard by which astronomers measure the apparent brightness
of objects that appear in the sky. The lower the number, the brighter
the object. The brightest stars in the sky are categorized as zero or
first magnitude. Negative magnitudes are reserved for the most brilliant
objects: the brightest star is Sirius (-1.4); the full Moon is -12.7;
the Sun is -26.7. The faintest stars visible under dark skies are around
+6.
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