by Jim Maynard
Star date: 03:05:97
Comet Hale/Bopp, showing signs of becoming
one of the greatest comets this century, is poised to enter the evening
sky around March 16. Look for it in the western sky just after sunset.
By March 1st it was already brighter than comet Hyaukutake at that comet's peak last spring, and was sporting the same length tail as Hyaukutake did, as seen from the Earth. People need no special equipment to see this, as the comet is glaringly obvious even from urban regions. A pair of binoculars will reveal far more of the tail than the eye can see alone, and a telescope can show fine detail in the head of the comet.
Comet Hale/Bopp was discovered July 23, 1995 by two amateur astronomers, Alan Hale and Thomas Bopp. Both were observing the nebula M70 in the constellation Sagittarius when they independently stumbled across a blur which was not supposed to be there, and could not be found on any star chart. Alan Hale has a Ph.D. in astronomy, but is only an amateur astronomer. Thomas Bopp, who did not even own a telescope at the time (he was borrowing a friend's) had never before seen a comet (Hyaukutake would not even be discovered until January, 1996).
Bopp ran to his car to report his discovery,
but his cellular phone was out of range. He drove to a truck stop and tried
using a pay phone, but could not find the phone number for the Central Bureau
for Astronomical Telegrams in Massachusetts (where all such discoveries
are reported). He tried information with no luck. He then drove the 90 miles
back home, found the number, and tried dialing. Unfortunately, it was a
Sunday and the office was closed. Finally, he called Western Union and sent
a telegram announcing his discovery. They called back the next day to confirm
his discovery, and congratulated him.
Comets originate in one of two clouds of rocks and ice.
One, enclosing our solar system, the Oort cloud, or the Kuiper belt, which
lies in a ring around our solar system.
The more distant of these, the Oort cloud, lies some 20,000-150,000 times the distance away from Sun than the Earth does (this can be expressed as 20,000 to 150,000 au, meaning "astronomical units". Each au is about 150,000,000 kilometers (93,000,000 miles). The Oort cloud is thought to be responsible for the formation of long period comets (these are comets whose orbits are measured in the dozens of thousands of years). The Kuiper belt is postulated to lie beyond Jupiter, in line with the planets. This Kuiper belt, first proposed by Gerard Kuiper in 1951, is quickly winning widespread support among astronomers as being the ultimate origin of short period comets.
One
of the greatest comets in recent memory is the great comet of 1811, mentioned
in the novel, "War and Peace". Like comet Hale/Bopp, the great
comet of 1811 was discovered long before it's peak brightness. It remained
visible to the unaided eye for nine months; a record yet to be surpassed.
The year
1910 was stocked with two wonderful, large bright comets. The first of these
would become known as the Great Daylight Comet of 1910. The second comet
of the year was Halley's a few months later. The former was far greater
than that year's apparition of Halley's (Halley is not really that great
of a comet, despite many people's belief. It is just the first comet whose
return was predicted. This was done by Sir Edmund Halley, who never lived
to see his namesake's return.).
Comet Ikeya/Seki outshone the full Moon by some 60 times when it made it's appearance in 1965. Unfortunately for northern hemisphere observers however, Ikeya/Seki peaked over the southern hemisphere, putting on it's most spectacular display for Japan and similar latitudes. The disappointment over comet Kohoutek (a comet for which high hopes were originally raised and then later dashed as the comet fizzled in 1974) was alleviated when comet West made it's appearance in 1976.
This comet was, in one important aspect, the antithesis
of comet Kohoutek; it appeared to be a run of the mill comet until just
a week before it's peak when it suddenly brightened beyond the brightest
stars at the end of February.
Comet West
then shattered into four pieces, which then slowly dimmed for the next month.
The only comet to appear within the memory of those college age or younger
was comet Hyaukutake in 1996.
Comets are, essentially, dirty snowballs which grow tails
as they scream in their orbits around the Sun. Some may have orbits of only
a few years (these are known as "short period comets") and others
like Kohoutek only come in towards the Sun once every 80,000 years or more.
These comets may travel more than 100 times as far away from the Sun as
the planet Pluto. Halley's is regarded as a short period comet because it's
orbit is repeated once every 76 years. It was this short orbit which gave
away the fact it was one comet.
When Sir Edmund Halley was studying a list of different recorded comets,
he noticed that a comet was recorded coming from the same area of sky every
seventy six years. He postulated that they were all the same comet. He was
correct. Hale/Bopp, it is believed, had an orbit of around 4,000 years.
A recent approach to Jupiter changed it's orbit so it now will be circling
the Sun every 2,500 years.
On Sunday
March 23rd, in addition to being the night which Hale/Bopp will be at it's
grandest, will offer a lunar eclipse. Not all of the Moon will be in Earth's
shadow, but over 90 percent of the Moon will be eclipsed. This will be the
last lunar eclipse visible from this area until January 21, 2001.
More on this eclipse next week.
Good viewing to all, and clear skies.
James Maynard is head of the astronomy department at Earth Treasures in Keene, N.H.
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