This week will be especially interesting for skywatchers
because of a fine array of bright planets in our evening sky. In fact, four of
the five bright naked-eye planets are now readily visible beginning about 45
minutes after sundown.
Venus is the most obvious. It is bright enough to show
through the blue sky soon after sunset. Even though its greatest elongation
from the Sun won't be until June 9, Venus reaches the summit of its current
evening apparition this month, appearing at its greatest height in the evening
twilight for the year 2007.
Venus now shines at a dazzling magnitude of –4.2 (more than
13 times brighter than Sirius, the brightest
star in the sky) and stands nearly 40-degrees above the western horizon at
sunset (your clinched fist held at arm's length measures roughly 10-degrees in
width; so 40-degrees is roughly "four fists" up from the horizon).
Venus is now staying up very late, well past 11 p.m. for
many locations. On Saturday, May 19, Venus and the crescent Moon will make for
a stunning
sight for North Americans, as the two objects will descend down the western
sky side-by-side, only about one degree apart. I wouldn't be at all surprised
if local media outlets receive a bevy of phone calls that evening all asking
what that "strange light" (or UFO) is to
the left of the Moon.
Jupiter lights up
Meanwhile, another brilliant light is pushing its way up
into the southeast sky during May evenings: Jupiter. This week the giant planet
rises around 9:30 p.m. local daylight time; by month's end, it's rising closer
to 8:30 p.m. and is already above the horizon as darkness falls. Jupiter shines
at a brilliant magnitude of –2.6 (about one-fourth as bright as Venus). To its
right or lower right is Antares, the red 1st-magnitude heart of Scorpius, the
Scorpion. The full Moon will be passing to the south of Jupiter during the dawn
hours of June 1.
Consider some of the contrasts between Venus and Jupiter: Venus is a sister
Earth in size, but so shrouded in dense, hot clouds of carbon dioxide that its
brilliance in our sky is largely due to its high reflectivity (about 76
percent). Jupiter on the other hand, is an entirely different type of
planet—gigantic, surrounded by a thick atmosphere composed chiefly of methane
and ammonia, and icy cold. Ordinarily it appears second only to Venus in
brightness, its remoteness being compensated by its great size. Its surface
area is 130 times that of Venus.
And have you ever wondered how the ancient Romans happened
to name Jupiter after the most powerful of their gods, even though they knew
nothing of the planet's physical characteristics?
Spot Saturn, too
Sitting roughly in between Jupiter in the southeast and
Venus in the northwest is the ringed beauty of our solar system, Saturn.
Saturn appears as a moderately bright yellowish-white "star"
very close to the border between the zodiacal constellations of Leo and Cancer,
and about 11-degrees west (to the lower right) of Leo's brightest star,
Regulus. Saturn can be found more than halfway up in the southwest sky as
darkness falls during May. It will set this week at around 1:30 a.m. local
daylight time; about an hour earlier by month's end.
A telescope magnifying 30-power or more will reveal that the
famous ring system is tilted about 17-degrees from our line of sight. The
nearly first-quarter Moon will lie to the left of Saturn as darkness falls on
May 22.
Last but not least
Finally, late May provides us with an especially favorable
apparition of Mercury for Northern
Hemisphere observers.
This orange-yellow-hued planet currently rivals all the
stars in brightness save for the two brightest, Sirius and Canopus. It can
easily be picked up in binoculars shining through the Sun's bright afterglow.
Just look for it far to the lower right of Venus near the west-northwest
horizon; Mercury will be the brightest starlike object down there.
Mercury has its best evening apparition of the year during
these next two weeks (for observers in the Northern Hemisphere), as an easy
naked-eye object and setting near the close of evening twilight. Although
slowly fading, the little planet gains altitude rapidly day by day. By May 27
it climbs to within 22-degrees of Venus. Then, for about the next ten days
these two planets will seem to stay almost fixed in their respective positions
above the dusk horizon.
On June 2, Mercury will stand at greatest elongation,
23-degrees east of the Sun. During the following week it will rapidly fade as
it circles back into the glow of the setting Sun.
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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