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David Levy's popular Radio talk show, broadcast
live, daily from Tucson, Arivona
A newly discovered comet, now approaching the Sun and
Earth, could develop into a relatively bright naked-eye object
in coming weeks, researchers say. The best views of the
comet may be reserved for those under dark skies far from
bright lights, but even city dwellers should be able to spot it.
Kaoru Ikeya of Japan and Daqing Zhang from China first
sighted the comet in the constellation Cetus, the Whale, on
Feb. 1. Both described it as a weak, condensed glow in their
telescopes with no mention of a tail.
The comet is called Ikeya-Zhang. The latest orbit calculation
indicates it will pass closest to the Sun, a point called
perihelion, on March 18 at a distance of 47.1 million miles
(75.8 million km). After rounding the Sun, the comet will
continue moving toward Earth, making its closest approach to
our planet, called perigee, on April 28, when it will be 37.6
million miles (60.5 million km) away.
Ikeya-Zhang's expected path across the sky in the coming
weeks will greatly favor Northern Hemisphere observers.
During most of March on into early April, the comet will be
visible near to the north-northwest horizon about an hour after
sundown. Bright moonlight may hinder observations during
the last week of March.
After the first week of April, with the Moon no longer a factor,
the comet will also be visible in the morning sky, rising earlier
and getting progressively higher above the northeast horizon
each night.
Seen before?
Initially, it appeared that this comet would not get brighter
than fourth magnitude, which is similar to the brightness of a
relatively dim star. Magnitude is a measure of a celestial
object's apparent brightness.
But John Bortle, a longtime comet consultant for Sky &
Telescope magazine, said it could get brighter.
Soon after Ikeya-Zhang’s orbit was calculated, some orbital
specialists noticed a similarity to a pair of much earlier
comets that appeared in 1532 and 1661, Bortle explained in
an e-mail interview last week. The 1532 comet, in particular,
was apparently a bright comet according to Oriental records.
Brian Marsden of the Smithsonian Astrophysical Observatory
in Cambridge, Massachusetts, an orbital specialist, said last
Thursday that "a revolution period of 400-500 years (for
Ikeya-Zhang) is likely," keeping alive speculations that this
may be a return of the 1532 comet.
The key to figuring out if the comets are the same may lie in
Ikeya-Zhang’s orbital period -- how long it takes to go around
the Sun.
"In recent days, several observers have made their own
independent calculations suggesting that Ikeya-Zhang might
have an orbital period of roughly 500 years, making for a
strong argument that there may indeed be a direct connection
with the comet of 1532," Bortle said.
What to expect
How comet Ikeya-Zhang ultimately performs is anyone’s
guess. So far it is brightening more rapidly than originally
expected. As of late last week, it had nearly doubled in
brightness in just one week and was at magnitude 6.8 as of
Feb. 15.
But Terry Lovejoy, an assiduous comet watcher from
Australia, says it's a bit early to get excited.
"We’ve seen this situation before," Lovejoy cautions. "At first
a new comet appears to brighten at a much faster than
normal rate, but then as it gets closer to the Sun it seems to
run out of puff. My best guess is that this comet will be no
different and will peak somewhere at around magnitude 3.5."
Such a brightness is just slightly fainter than Megrez, the star
in the Big Dipper that joins the handle with the bowl.
"A peak of magnitude 3.0 would not be at all surprising to
me," says Bortle, adding that he expects Ikeya-Zhang to
unfurl an impressive tail perhaps up to 15 degrees in length as
it sweeps by the Earth. For comparison, your fist held at
arm's length measures roughly 10 degrees. However,
because this tail is likely to be chiefly composed of gas and
not dust, it will appear faint and bluish and likely only be
visible to those with access to dark skies free of light
pollution.
So how might Ikeya-Zhang stack up against other popular
comets?
The 1986 appearance of Halley's comet, considered
disappointing by many, also peaked at around magnitude 3.0.
In contrast, comet Hale-Bopp, which put on a memorable
show in April 1997, attained a brightness close to magnitude
-1, or about 60 times brighter than Halley.
Binoculars or a small telescope should allow most
skywatchers a view of Ikeya-Zhang's fuzzy head, called a
coma, and of the tail.
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