Tumbleweed Observatory's

Astronomy Hints



Observing Comets -- Equipment Required and Viewing Tips

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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 interest.

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.

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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 Comet
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 sun.

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
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 equipment.

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

Bushnell Binoculars

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 comet enjoyment.

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 view.

Photographing Comets

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.

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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.

Piggyback Camera 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.