Not since comet Hale-Bopp wowed observers in 1997 has a bright comet graced our skies. But that’s changing: 2013 brings us two comets, Pan-STARRS and ISON, and both may be visible to the unaided eye.
The first, comet Pan-STARRS, will be observable from the Northern Hemisphere in March, having already beguiled sky watchers in the southern half of our planet. Prime viewing days are predicted to be March 12 and 13. You’ll need a clear view of the western horizon away from light pollution. Look for the comet at twilight, low on the horizon and not far from the sliver of the moon.
You should see a bright point of light (predicted to be as bright as the stars in the Big Dipper) with a fuzzy tail pointing straight up—although you’ll likely need binoculars to see the tail. For comet enthusiasts, the chance to see a comet “naked eye” is a thrill—and a notable experience for anyone—but binoculars are a good idea nonetheless. As the month progresses and Pan-STARRS moves farther from the sun, it will become increasingly difficult to see, even with binoculars or a small telescope. But in April, it may be visible in the northern sky during the night.
If Pan-STARRS is exciting, ISON could be breathtaking. It’s a large comet and a “sungrazer” as well. On November 28 it will pass within about 600,000 miles (1,000,000 km) from the surface of the sun—which, as cometary orbits go, is quite close. It’s possible that it will be as bright as the moon, visible even during the day. And a huge tail to awe nighttime spectators may make it “the comet of the century” as some folks have already dubbed it.
But ISON’s close approach to the sun courts danger as well as glory. The sun’s radiation and tidal forces have completely shattered comets that ventured too near. If ISON leaves the solar atmosphere unscathed, however, it will be seen for months in the Northern Hemisphere’s night sky.
Comets: The Basics
The body of a comet, called the nucleus, is a mixture of dust particles, water ice, and ices of several gases. Comets travel around the sun in orbits that are mostly highly elliptical. If they near the sun, the solar heat releases gas and dust from the nucleus, which form a large temporary cloud, called the coma, around it. Solar radiation can push dust away from the coma, while the solar wind can push gases in a slightly different direction, creating tails that can extend for millions of miles.
Where Comets Come From
An immense number of comets reside in the outer reaches of the solar system—in the Kuiper Belt and the Oort Cloud—but only a few of them ever come our way. Of those that do, many show up only once in thousands or millions of years. Comets Pan-STARRS and ISON are both first-time visitors. Others are frequent guests of the inner solar system such as Halley’s comet, which appears, on average, every 76 years, and Encke’s comet, which goes around the sun about every 3 years.
Why Comets Matter
Apart from the spectacular light show that a great comet provides, comets are scientifically important. Scientists think that comets were formed during our solar system’s birth. Inhabiting the frigid fringes of the solar system, far from the sun and immune to the evolutionary changes that the earth and other planets have experienced, they may well contain the best-preserved record of our solar system’s beginnings.
But that’s not all. A current study (published in the Astrophysical Journal March 10, 2013) has found that biological compounds can develop in space. The authors suggest that the seeds of life, rather than originating on earth, may have been delivered to our young planet by bombarding comets, which also provided life-supporting water.
Video about the Current Comets
For additional information about the 2013 comets, see this Science @NASA video.