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057

comets

OLogy Series
astronomy
card
057

comets

OLogy Series
astronomy

Comets are like "dirty snowballs" that have orbited the Sun since our Solar System formed, billions of years ago. A comet is really just a round chunk of ice and dust. The ball-like part of the comet is called the nucleus, and its long "tail" is called the coma. The coma forms as tiny bits of the nucleus break down and fall off. As solar winds sweep away this dust the whole comet appears to glow.

The Most Famous Comet in History
Halley's Comet has been seen by generations of people. This famous short period comet can be seen every 76 years and is named for the astronomer Edmund Halley. He was the first to notice that three different comets that were documented in 1531, 1607, and 1682 all had the same orbit. He boldly declared that all three were actually the same comet and that it would return again in 1758. He was correct! Too bad for Edmund -- this was 16 years after he died. In honor of his amazing discovery, the comet was named Halley's Comet. Halley's Comet will pay our solar system another visit in the year 2061. Maybe you'll see Halley's Comet with your grandchildren!

A comet's life can end when:

it runs out of food and water

it loses its map of the Universe

the gravity of other planets causes it to break

Are you right?

Correct!

Sometimes comets "die" when they are broken apart by the gravitational pull of other planets. Shoemaker-Levy 9 was a comet that was pulled apart by Jupiter's gravity in 1994.

Where are most of the comets in the solar system found?

under the kitchen sink

hiding in Martian craters

in the Oort Cloud

Are you right?

Correct!

The Oort Cloud is a ring of comets at the solar system's edge. We only see a comet from Earth if it leaves the Oort Cloud when it orbits the Sun. Only 135 comets do this more than once in 200 years. We call them short-period comets.

A comet's tail always points towards the Sun.

Fact
or
Fiction
?

Fiction

Actually, the opposite is true. Gas and dust in the coma are pushed away from the Sun by the solar wind.

The coma, or the part of the comet that is surrounded by gas and dust, can grow to be hundreds of thousands of miles in length.

Fact
or
Fiction
?

Fact

The Great Comet of 1811 was one of the largest comets recorded. Scientists believe that the coma reached lengths of over 800,000 miles across!

Number of Comets: 750 identified, about 10 trillion others
Where: in the Oort Cloud
Types: Short-period and long-period comets
Typical size: 6 miles wide
Composition: lumps of ice, dust, and rock
Significance: give astronomers clues to how the solar system formed

Image credits: A Star Cluster Through Hale-Bopp's Tail, A. Dimai, R. Volcan, D. Ghirardo (Col Druscie Obs., ACC).