January 25, 2008

Spectacular Sky Show: Venus, Jupiter and the Moon

The most spectacular celestial sights over the next couple
of weeks are reserved for the early morning sky. Two bright planets will
converge, then be joined by the moon.

Kenneth L. Franklin (1923-2007), the former Chairman and
Chief Astronomer at New York's Hayden Planetarium, would often make reference
to our "dynamic and ever-changing sky."

Such an eloquent description certainly fits our current
morning sky, for these final days of January and the first days of February will
be an exceptional time for predawn sky watchers with a beautiful pairing of the
two brightest planets, Venus
and Jupiter.
They will appear closest together in the dawn sky of Friday, Feb. 1, and a few
mornings later, the waning crescent moon will later drop by to join them.

Dazzling "double planet"

For the past several months, dazzling Venus has been prominent
in our morning sky. And about a week ago, brilliant Jupiter also began to emerge
from out of the glare of the Sun.

The two planets are currently rising out of the
east-southeast horizon about two hours before sunrise.

From now through the end of January, the gap between the two
will noticeably close, until on Feb. 1 they'll be separated by just over
one-half degree, which is roughly the apparent width of the moon (The width of
your fist, held at arm's length roughly corresponds to 10 degrees). Jupiter
will shine brilliantly at magnitude -1.9, yet it will appear only 1/7 as bright
as Venus, which will gleam at magnitude -4.0.

Together they will make for a spectacular "double
planet" low in the dawn twilight. In the mornings thereafter they will
appear to slowly separate, but before they have a chance to get too far apart
the moon will join the picture.

Celestial summit meeting

At last quarter (half) phase on Jan. 30, the moon will stand
alone, high toward the south at sunrise. But with each passing morning, as it
wanes to a slender crescent, it will shift toward the east, ultimately into the
same region of the sky as our two planets.

Early on Sunday morning, Feb. 3, the moon will sit well off
to the west (right) of the planets. On the following morning, Monday, Feb. 4,
the show will reach its peak when, about 45 minutes before sunrise, Venus,
Jupiter and the moon — the three brightest objects of the night sky — will form
a striking isosceles triangle, with the two planets 3 degrees apart and the moon
marking the vertex of the triangle just over 5 degrees below the "dynamic

Imagine the astrological
that the ancients might have ascribed to a celestial summit
meeting such as this!

You might want to check your southeast horizon in advance to
make sure that there are no tall trees or buildings that might obstruct your
view of the moon which will be sitting very low to the horizon.

Like a painting, this celestial tableau might, at first
glance may appear rather flat and one-dimensional. But by gazing at this scene
long enough, our minds can perhaps picture these objects strung out across the
solar system, along our line of sight as they really are.

Beyond our moon — figuratively a stone's throw away at
247,000 miles (397,000 kilometers) — we first reach Venus, about 510 times
farther out, or 126 million miles (203 million kilometers) from Earth. The lesser
gem flanking Venus — Jupiter, largest of all the planets — is nearly 4 and a
half times more distant than Venus at a distance of 560 million miles (901
million kilometers).

Generally speaking, at least for the immediate future,
conjunctions between Venus and Jupiter will come in pairs. The first
conjunction takes place in the morning sky, followed about 10 months later by
another in the evening sky. Then, after about two and a half years, Venus and
Jupiter are again in conjunction, again in the morning sky.

When Venus and Jupiter next get together, it will be in the
evening sky late next fall, on Dec. 1. After that, we'll have to wait until May
2011 (morning sky) and Mar. 2012 (evening sky) for the next set of
Venus-Jupiter conjunctions.

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.