The planet Venus passed conjunction with the sun on
June 9 and is now emerging into view in the western evening sky. But it will be
a long and tedious process. Even by the end of September this planet will still
very low at dusk.
Look for Venus just as evening twilight fades, but don't
wait too long, for it will set only about an hour after sunset. Scan just above
the western horizon about 20 to 30 minutes after the sun goes down. Binoculars
will certainly help you pick out Venus' silvery spark from the still-bright
sky. As the season grows cooler Venus will slowly rise higher, until it shines
as a brilliant "evening star" in the twilights of winter.
But Venus is currently not alone, for also nearby are the
planets Mercury and Saturn.
Over the past week these three planets have been clustered
rather closely together. Unfortunately, their close proximity to the sun caused
these planet bunchings to be visible only with difficulty against the bright
backdrop of evening twilight. They are still relatively close together this
week, although all three are so very low to the western horizon and so deeply
immersed in the bright sunset glow that it is debatable that aside from Venus
that the other two planets will be observable.
Your best bet is to use binoculars and scan near the western
horizon about 15 to 30 minutes after sunset.
Swap in Mars
In September, Saturn disappears into the fires of sunset and
is replaced in the planet trio by Mars. So it will then be Venus, Mercury and
Mars that will spend much of September tightly grouped together. Unfortunately,
their proximity to the sun will continue to be a problem, so they'll continue
to be visible only with difficulty against the bright backdrop of twilight.
Using binoculars and scanning the horizon somewhat to the
south of due west about 15 to 30 minutes after sunset on Sept. 1, you just might
be able to pick up Venus, Mercury and Mars forming a right triangle. And below
and to the left of this planet trio will also be a narrow crescent moon just
2.1 days past new.
Viewers in the southern U.S. will have a bit of an advantage
in that this group will appear a bit higher above the horizon.
Planet shuffles
On Sept. 7, the Venus-Mercury-Mars grouping will resemble an
isosceles triangle,
with the Mars-Mercury and Mars-Venus sides measuring about 2.5 degrees in length
and the Mercury-Venus side about 4 degrees. And located about 10 degrees
(roughly the width of your fist held at arm's length) to the upper left of the
triangle will be Spica, the brightest
star of the constellation Virgo.
Venus and Mars will be separated by only 0.3 degree (less
than the apparent width of the moon) on Sept. 11. If you can locate Venus with
binoculars in the twilight, Mars will be situated just below and to the left of
Venus. Mars will appear only 1/174 as bright as dazzling Venus, so don't expect
to see it right away.
The next evening, Venus is in conjunction with Mercury, but
they're more widely separated at 3.6 degrees; Mercury will appear below and to
the left of Venus. At magnitude +0.2, Mercury is much brighter than Mars, but
still only 1/44 as bright as Venus. And creeping in from the east is Spica, about
7 degrees to the upper left of the three planets.
Come Sept. 18, Venus, Mercury and Mars will form an
equilateral triangle, whose sides are 4 degrees in length. And Spica now
becomes a part of this array, sitting only a few degrees to the left of the
triangle. Whether you'll actually be able to see it, or the even fainter Mars
against the backdrop of the bright twilight sky, however, is debatable.
But to have three planets and a bright star crammed into a
relatively small spot in the sky does not happen very often, so I would urge
you to give it a try.