How To Observe Comets
Comets appear to be the oldest objects in our solar system. The ancient
nova that spewed out the materials from which our Solar System is
composed created the elements and compounds that created the comets.
Comets are often referred to as dirty snowballs. They are composed of
water ice and rocky materials. They also contain a lot of carbon rich
materials. In recent years, comets have gained interest as the possible
building blocks of life.
Comets are believed to exist in great numbers in a distant shell
around the Sun called the Oort cloud. Because some are rather large,
and the fact that collisions or near encounters occur in the cloud,
comets sometimes get dislodged from their stable, distant orbits. When
this happens, they end up in highly elliptical orbits that take them
near the sun.
When comets come close enough to the Sun, the frozen water begins
to melt and turn into vapor. The vapor and dust on the comet become
dislodged and become visible as a tail on the comet. Every 10 years or
so a comet becomes easily visible to the naked eye, and grabs enormous
The many meteor showers we experience each year are the result of the
Earth plowing through debris from comets whose tails of dust extend into
the Earth's orbit.
Comets Come In Many Forms
When comets come into the vicinity of the sun, they can look spectactular.
When Halley's Comet
made a close approach in 1910, it provided a wonderful show. Yet when it
returned in 1986, it was hardly awesome. What was different? The main thing
was that in 1910, Earth passed within about 14 million miles of the comet. In
1986, the comet was several times further away.
Hale Bopp Photograph - 1997
The image above is that of comet Hale Bopp, taken in 1997 with a
Piggyback Camera Mount. As you can see, it made a beautiful target. Not all comets that
come into backyard view will be as nice as this one.
This photo shows the blue ion trail and the yellowish dust
trail. The dust trail is the flaked off material, and gives a bit of
history as to the path of the comet. The ion trail is made from ions driven
away from the comet by the solar wind, and always moves directly away from the
Certainly, not all comets become this grand. Many are observable only with
some kind of optical aid. As an example, examine the images below. To the left
a drawing of comet
17/P Holmes, made in October of 2007. To the right is a photo of the same
comet, taking a couple of weeks later.
The photo, also taken with a piggyback camera, reveals the comet as the
largest white area, and is poorly exposed in this picture. It was, however,
taken with equipment similar to that used in the Hale Bopp image. Notice that
this comet appeared much smaller, and showed no tail.
Holmes Comet Drawing
Holmes Comet Photograph
Most comets you will get to see from your backyard more resemble the
17/P Holmes comet, but every few years something more like Hale Bopp will
take center stage.
What's the Best Way to Observe Comets?
First, be informed of what comets are visible, and where they are located.
While the spectacular naked eye comets don't happen that often, comets that
are just discernible to the naked eye occur perhaps every couple of years.
And even those objects are very nice objects when viewed with modest
For comet observing, you need get up to date information. Because comets are
fast travelers, they usually make their revealing runs in a short time -- weeks
to a few months. And since they move so fast, in only a few days time they can
change their celestial position significantly. A couple of useful websites that
present up to date comet information are Weekly Information about
Bright Comets and Comet Chasing.
For observing comets, transparency and sky glow from interfering lights
is your primary problem. The best thing you can do for starters is
find a dark site from which to observe.
What You Need to View Comets
Comet observing requires the widest field instruments you can obtain. The
best place to start, and perhaps even end up, is with a decent pair of
binoculars. You needn't get high power binoculars either. A pair of the popular
and readily available 7x50 binoculars work nicely.
I have 3 pair of binoculars which have been collected over time. I use a 7x50, a
16x50, and a 15x70 pair. I could easily do with two. I like the 7x50 pair for
locating comets, and observing those with well developed tails. I use either of
the other two pair to get closer views of comets like 17P/Holmes, which don't
become so extensive.
You could also get a short focus, wide field telescope for viewing less
distinct comets, or for better viewing of the center cloud of comets. I use a
6" f/5 Newtonian telescope. The Holmes comet fits nicely in the field of view
of the short telescope. Longer focus instruments generally have too narrow of
fields of view to let you enjoy the beauty of a comet.
Instruments that work well are the 3 inch and larger short refractors now
available, and short focus 4 to 6 inch Newtonian telescopes. Longer focal ratio
telescopes tend to have fields of view that are rather narrow for the extensive
views most suited to comets. While short ratio Newtonians of larger apertures
are certainly available, they too began to have limited sized fields of view for
You can use the following table to see telescopes that work well for
observing comets. In the table, concentrate on examples in the lower-left
portion. These are small to moderate sized instruments with wide fields of
Comets are actually among the easier targets for astrophotographers. This
is because you don't need a powerful instrument, and you do not generally
take high magnification photos of comets.
You need a camera, and often you can don't even need a camera with
a telephoto lens. A 35mm works well, and is probably the cheapest
alternative. You need one that will let you take time exposures. If it
can take telephoto lenses, that's a plus.
Use this astro-customized search engine to find cameras, telescopes, and
accessories for astrophotography.
One simple device you can make to help you photograph constellations,
interesting regions of the Milky Way, and comets is a thing called a Barn Door
mount. A barn door mount is basically a pair of boards fastened together by a
large hinge, with a tangent arm motor drive that opens or closes the hinge at
the same rate the Earth rotates.
By aligning the hinge axis with Polaris, this simple device allows a
camera to be kept pointed at a particular point in the sky long enough for
a time exposure. Since often a normal camera lens is sufficient for catching
a comet, this is probably the simplest approach.
A couple of websites that give simple instructions for making a barn door
mount are A "Barn Door" Mount and Barndoor Mount.
If you have a clock driven telescope, you can also use piggyback
photography. At left you see the setup I use to do wide field astrophotography.
This is a piggyback mount affixed to my 6 inch f/5 Discovery EQ telescope.
Since the telescope has a clock drive, I simply lock open the shutter on
my camera and use the telescope to be sure I stay on target.
Check out my Piggyback Photography page for more information.