[meteorite-list] Last Chance to See Bright Comet Ikeya-Zhang

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:50:29 2004
Message-ID: <200204261525.IAA01397_at_zagami.jpl.nasa.gov>

http://www.space.com/spacewatch/ikeya_zhang_020426.html

Last Chance to See Bright Comet Ikeya-Zhang
By Joe Rao
space.com
26 April 2002

It's time to bid farewell to the brightest comet to appear in five years.
Ikeya-Zhang, discovered Feb. 1, will soon end its run as a naked-eye object.
It will then zoom to the outer reaches of the solar system, not to return
for another 341 years.

Meanwhile, there are a few days left to spot the comet some observers have
come to call Izzy.

Ikeya-Zhang made its closest approach to the Sun, called perihelion, on
March 18. At the time, the comet was just 47 million miles from the Sun,
roughly midway between the orbits of Mercury and Venus. Although the comet
has been moving away from the Sun ever since, it has been steadily approach
the Earth.

On April 29, Ikeya-Zhang will pass as close to the Earth as it will come
during this apparition, 37.6 million miles away.

Because the comet has been approaching the Earth during the past six weeks,
its fade-down since sweeping around the Sun has been slow, as expected. The
comet apparently remained as bright as magnitude +3.5 from March 18 through
April 8. It probably achieved peak brightness on April 1, when it reached
magnitude +3.2, just a trifle brighter than Megrez, the star joining the
bowl and handle of the Big Dipper.

For nearly three weeks, the comet's approach to Earth had nicely compensated
for its increasing distance from the Sun.

Since April 8, however, the comet's fading has been more noticeable. It is
now a fourth magnitude object -- easy enough to still see if you have a good
dark sky, but more challenging from a city.

The comet has also been sporting a fine tail at least several degrees in
length (your fist held out at arms length is roughly equal to ten degrees;
the "Pointer Stars" at the end of the bowl of the Big Dipper are just over
five degrees apart). While the best views of the comet have been in the
predawn morning sky through much of April, the Moon -- full on April 26 --
will now be flood the late night and early morning sky with its reflected
sunlight during the coming week.

So it will now be better to look for the comet in the evening sky, beginning
about an hour after sundown until the Moon rises later at night.

Izzy rules

During the past three weeks, despite the fact that it began to slowly fade,
Ikeya-Zhang was still getting excellent reviews from observers around the
Northern Hemisphere.

Jakub Cerny of Senohraby, Czech Republic was blessed with perfect sky
conditions on April 5. Skies were so dark and clear that he was able to see
stars down to seventh magnitude (the threshold of naked eye visibility is
considered to be sixth magnitude). Against that type of backdrop,
Ikeya-Zhang was impressive.

"I've seen a really great comet now," Cerny said, adding that the comet's
ion tail, composed of gas that reflects sunlight, appeared 4 degrees long
and its dust tail 2½ degrees in length.

Contrary to popular conception, comets typically have two tails.

Observing from Caldwell, Ohio on April 7, Phillip J. Creed said, "As Keanu
Reeves once said in 'The Matrix,' ' . . . whoa.' (An) unbelievable binocular
object under a dark sky; the tail stretched 5.7-degrees across in 10x50
binoculars, with some curvature evident after 2 degrees. In dark skies, Izzy
just rules!"

Izzy is short for short for I-Z, which of course is in turn the acronym for
Ikeya-Zhang, named after its co-discoverers Kaoru Ikeya of Japan and Daqing
Zhang of China.

The co-discoverer of the famous comet Hale-Bopp, Alan Hale, viewed the Izzy
on April 10 from Cloudcroft, New Mexico. "A lovely object in almost any
instrument," Hale wrote.

Some observers have been plagued by bad weather and as a result have had to
move to a different location to see Ikeya-Zhang. Astronomer Charles S.
Morris had to head to the mountains of Southern California to escape
spring's low clouds and fog in the morning. On April 13, Morris estimated
that Ikeya-Zhang's tail was "perhaps as long as 7-degrees" from Atascadero,
California, "a very dark location."

Robert B. Slobins had to maneuver around DeKalb County, Indiana in order to
see Ikeya-Zhang on April 16. "The comet was plainly visible to naked eye,
but this is the first time in weeks that I have seen it thanks to the
absolutely terrible observing conditions that persist in Indiana."

What's next?

May early May, the comet will likely have dimmed to about fifth magnitude.

Fading more rapidly now, it should no longer be visible to the unaided eye
by about the middle of May. By month's end it should be down to about eighth
magnitude and will be strictly an object for good binoculars and telescopes.

Calculations by orbital experts such as Brian G. Marsden of the Smithsonian
have shown Ikeya-Zhang to be identical with another naked-eye comet that
appeared to sky watchers back in 1661. Thus, the comet of 1661 and
Ikeya-Zhang are apparently one and the same object. If so, then its orbital
period -- the time it takes to go around the Sun -- is roughly 341 years.

Given this reckoning Ikeya-Zhang should reach the far end of orbit, called
aphelion, about the year 2173, a distance of some nine billion miles from
the Sun. And with any luck, sometime around the year 2343, it should again
return to the inner solar system and the vicinity of the Sun and Earth.
Received on Fri 26 Apr 2002 11:25:24 AM PDT