by Randy Krippner
Comet Hale-Bopp has generated
more controversy than almost any other astronomical event in the past few
decades. But for the moment let’s leave the rumors about Hale-Bopp
companions, mysterious radio signals and connections with extra terrestrials
behind for a moment and take a look at what we do know about Hale-Bopp and
comets in general.
What Are Comets
Even though comets bright enough to be seen with the naked eye are
relatively rare, comets themselves are actually pretty common. Every year
astronomers spot about twenty or more comets. Most of these never make the
news reports in the popular press because they never become visible to the
naked eye. Comets often can never be seen with the naked eye, even at their
brightest. Only rarely does a comet become bright enough to become truly
spectacular. In the past couple of hundred years, only a handful of the
hundreds of comets that have zipped past the Earth on their journey around
the Sun have become bright enough to have been really noticeable.
What makes a comet such a spectacular sight is not how large it is, but what
it is made of. Comets actually are fairly small things when compared to
planets and stars. They generally range in size from just a few miles across
up to around 100 miles across. That makes them pretty insignificant when
compared to other objects in the Solar System.
It’s their composition that makes them different. You may have heard them
referred to as dirty snowballs, and that’s fairly accurate. Comets are made
up of frozen gases and water ice, often with a core of rock. As a comet
approaches the sun, it warms, and the frozen gases begin to thaw. It begins
to emit dust and gas as it warms. At first this vapor and gas remains close
to the nucleus of the comet, making it appear as a fuzzy looking object in
But as it comes closer to the sun and warms even more, more and more gas and
dust are thrown off by the comet, making it look larger and brighter than it
really is. The visible head of the comet is really a cloud of water vapor,
dust and gas surrounding the nucleus of the comet.
As it approaches even more closely, it begins to form a tail, which can be
millions of miles long. Comets actually have two tails. The most visible is
the dust tail made up of tiny particles of dust, gas and water vapor. The
other tail, the ion tail, can be even longer, but because it is composed
largely of plasma, the ion tail is usually visible only in long exposure
images taken through telescopes.
Other, often quite spectacular events can occur as the comet approaches the
Sun. Pockets of gas, exposed as outer layers of the comet erode away, can
suddenly burst forth, causing spectacular looking jets of material streaming
away from the comet. Large chunks of the comet can break away from the main
mass, or the comet can even fragment completely as
SL9 did in 1994 before it
Eventually the comet will lose most or all of its volatile material after
many passes past the sun. Once the gas and ice is gone, all that remains is
a rocky core that looks a lot like an asteroid. Many of the near earth
asteroids may be the remnants of comets.
Other comets come to a more spectacular end, as
Shoemaker-Levy did when it
crashed into Jupiter. In fact, some scientists believe Jupiter acts as sort
of a giant vacuum cleaner, sucking up stray asteroids and comets, and
sweeping the inner solar system free from debris. If it weren’t for
and it’s giant gravity well, the inner solar system would be littered with
debris that would come crashing into the Earth so frequently that it would
have made life here nearly impossible.
Although Hale-Bopp has attracted more interest because it is brighter than
most, it appears to be a fairly ordinary comet. It was discovered by two
people simultaneously on July 23, 1995; Thomas Bopp of Arizona and Alan Hale
of New Mexico, hence the hyphenated name, Hale-Bopp.
Hale-Bopp has a long orbit, taking about 3,000 to make it’s journey around
the sun. It will reach perihelion (its closest approach to the sun) on April
1, 1997, and will approach to within about 85 million miles of the sun. Any
comet that approaches that close to the sun has a chance of putting on a
pretty good show. (Some comets come much closer to the sun. One, Ikeya-Seki
in 1965, literally skimmed the surface of the sun, and quite a few get a bit
too close, and actually plunge into the Sun.)
Hale-Bopp’s closest approach to the Earth will be on March 23, 1997. It will
come within about 120 million miles of the Earth. In March and April it will
be easily visible from the Northern Hemisphere if it becomes as bright as
The latest estimate of the comet’s actual size (the size of it’s solid
nucleus, not the gas cloud surrounding it) puts it at around 25 miles in
diameter, about four times larger than Halley’s Comet. It’s very difficult
to estimate the size of a comet’s nucleus, however. Unless the nucleus can
be directly imaged by a spacecraft from close range, as was the case with
Halley, trying to accurately determine the size of the nucleus is extremely
So far Hale-Bopp resembles every other bright comet that has visited our
part of the Solar System in the past, and like
("click" to enlarge)
every other bright comet, it
has generated a considerable amount of rumor, speculation and odd stories.
The most prominent story
about the comet is the Shramek photo (right). In the middle of November,
Chuck Shramek of Houston took a photo of the comet that shows a
bright, Saturn-like object near the comet. Mr. Shramek claimed that
this was a large object moving along with the comet. Soon others
came forward making even more astonishing statements; that the
object was actually an
enormous space ship, that it was emitting
radio signals, and that there was a government conspiracy to hide
the fact that this ship was moving towards the Earth. Some have even
claimed that the comet has changed course due to the influence of
Copies of the Shramek photo have
cropped up all over the Internet, and every professional astronomer who has
seen it has said the same thing, that the Saturn-like image is just a star
surrounded by diffraction spikes or some defect in the telescope’s optics.
I’m an amateur astronomer myself, and I’m familiar with the way images can
be distorted by flaws in optics and obstructions in the light paths of
telescopes. I have to admit that it does look like a distorted star image.
However, the only star in that position is a 9th magnitude star that should
appear only as a pinpoint of light, while the object in this image is nearly
as large as the comet. If the object is indeed caused by a defect in the
telescope or diffraction spikes, would that also have caused the object to
appear this large?
Other claims simply don’t seem to make much sense. According to one, the
government is involved in a massive attempt to prevent the public from
gaining any information about the comet, and is suppressing all photos made
of the comet, and that no new images of the comet have been published since
The problem with the government suppressing information is that it would be
impossible for it to suppress everything. There are literally tens of
thousands of amateur astronomers out there, and many of them are equipped
with telescopes, cameras and CCD imaging systems that rival low end
professional equipment. Since Hale-Bopp is one of the brightest comets to
come along in recent years, almost all of those amateurs have been pointing
their equipment at the comet. There is simply no way the government could
suppress information from all of these sources.
And as for there having been no images of the comet published since May,
that simply is not true. A brief search of the Internet turned up almost two
hundred images of the comet that have been taken since August, with the most
recent that I’ve seen having been taken on December 6.
One of the more recent claims I’ve heard is that Hale-Bopp has
course, and was being influenced by an external agency, usually some sort of
extra-terrestrial force. Astronomers say this is not the case. They say that
scientists have simply refined the orbital path of the comet as more
accurate information about its position has been made available to them, and
that some people have misinterpreted the changes in the projected orbits.
The indications from all mainstream scientific sources is that Hale-Bopp is
simply another comet. Is it more than that? Only time will tell. Meanwhile
browse through the information we've provided here and see if you can make
sense of this mystery.