7th Grade Assessment – Unit 4 – RI.7.1, RI.7.2, RI.7.3, RI.7.4, RI.7.5, RI.7.8
Justice February 10, 2015
Read this article. Then answer questions 1 through 7.
Asteroids, Meteoroids, Comets
by Kenneth C. Davis
Where do asteroids like to hang out?
Asteroids, or “minor planets,” can be found all over the solar system, but most orbit the
Sun in an asteroid belt between Mars and Jupiter. Asteroids are space rocks that never
formed into a planet when the solar system was born. This is probably because of the
gravitational effects of Mars and Jupiter. Even if the asteroids had become a planet,
5 it would be less than one-quarter the size of Earth.
How many asteroids are out there?
Astronomers have found more than 20,000 asteroids since 1801 and discover more
every year. The largest asteroid, Ceres, was the first one found. Ceres is almost 600 miles
(970 km) across, or about one-quarter of the size of our Moon. But that’s pretty unusual.
Though a few asteroids are 150 miles (240 km) across or more, most are less than a few
10 miles wide and many are smaller than a car. There are more small asteroids than large
ones because the space rocks often crash into each other and break into smaller pieces.
(The little pieces become meteoroids, some of which are sent on a path toward Earth.)
That’s also why most asteroids are lopsided and full of craters.
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I have a head and a tail. I can move around, but you can’t take me for a walk. What am I?
A comet. Comets are dirty, rocky snowballs
15 that orbit the Sun. They spend most of their
lives far away from us, but when a comet’s
orbit brings it near the Sun, part of its frozen
“head” defrosts into a dusty, gaseous “tail”
millions of miles long. Then the comet appears as a
20 brilliant streak we can see in the sky for
weeks or even months. Since the pressure of
the Sun’s radiation—which is what pushes the
dust and gas away from the comet—always flows
away from the Sun, the comet’s tail always points
25 away from the Sun, too. That means that
sometimes the comet seems to travel backward,
with the tail leading the head!
Where do comets come from?
Most astronomers think that comets come from two places: the Oort Cloud, a huge
icy ring around the edge of the solar system, and the Kuiper Belt, a ring of planetary
30 leftovers inside the Oort Cloud. Comets that come in our direction have probably been
pulled in slowly because of the gravitation tugs of planets or passing stars.
All comets orbit the sun in a predictable period, or amount of time. Short-period
comets orbit at least once every 200 years and probably come from the Kuiper Belt.
Long- period comets take more than 200 years and most likely come from the Oort Cloud.
Edmond Halley (1656–1742)
As a student at Oxford University in England, Edmond Halley (rhymes with valley) was so excited about astronomy that he left school to map the stars in the Southern Hemisphere’s skies. Halley is best known for his groundbreaking work on comets, especially the one that bears his name. Halley was the first to say that comets sighted in 1531, 1607, and 1682 were actually the same comet returning every 76 years. He predicted the comet’s return in 1758, though he knew he wouldn’t live to see the prediction come true. When it did, the comet was named in his honor.
Astronomy was just one of Edmond Halley’s many strengths. Among countless other things, he developed the first weather map and studied Earth’s magnetic field. The multitalented Halley was England’s Astronomer Royal from 1719 until he died in 1742 at Greenwich Observatory in England.
Who’s coming to visit in 2062?
35 Halley’s Comet, the most famous of them all. Halley’s visits have been connected to
several historic events. The Chinese saw the comet in 240 B.C. and blamed it for the death
of an empress. The Romans recorded it in 12 B.C. and thought it was connected to the
death of one of their statesmen. In 1066, the Normans of France believed the comet
marked the invasion of England by William the Conqueror. (The comet is even shown on
40 the Bayeaux Tapestry, which records William’s victory.) Halley’s Comet also came through the
years the famous American writer Samuel Clemens—also known as Mark Twain—was born and died.
