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Set 4



DIRECTIONS: The passage in this test is followed by several questions. After reading the passage, choose the best answer to each question and WRITE THE ANSWER IN YOUR NOTEBOOK. You may refer to the passage as often as necessary. To have the questions open in a new browser window, CLICK HERE

After you have finished answering ALL of the questions, check your answers by clicking on the letter you have chosen. COUNT THE NUMBER OF ANSWERS YOU GOT CORRECT ON THE FIRST TRY, MARK IT DOWN, AND TELL ME THE SCORE



NATURAL SCIENCE: This passage is adapted from Mark
Littman's Planets Beyond: Discovering the Outer Solar System
(©1990 by John Wiley & Sons).



















     [From the surface of the planet Pluto,] we look up
at Charon in the sky, 20 times closer to Pluto than our
Moon is to Earth. It is an impressive sight. Charon may
rank twelfth in size among moons in the solar system,
but it is so close to Pluto—only 11,650 miles (18,800
kilometers) above Pluto's equator—that it appears
larger than any other moon appears from the surface of
its planet. Charon covers almost 4 degrees in Pluto's
sky—eight times as wide as our Moon appears from
Earth. On our planet, you can hold a pea out at arm's
length and completely eclipse our Moon. On Pluto, to
block Charon from view, you would need a billiard

     It was no surprise that Charon rotates in the same
period of time as it revolves so that it always presents
the same hemisphere to Pluto. All the inner satellites
and all the major satellites in the solar system have syn-
chronous rotation and revolution because they are
tidally coupled to their planets. A planet's gravity cre-
ates a slight tidal bulge in its moons and pulls on that
bulge so that the moons cannot turn it away from the
planet. One side of the satellite always faces the planet
and the other side always faces away while the planet
rotates rapidly, so that the moon rises and sets for all
parts of the planet.

     But Pluto furnished a surprise. Pluto and Charon
are so close to twins in size and so close together that
Charon's gravity induces a bulge in Pluto. The bulge is
great enough that Pluto is tidally coupled to Charon just
as Charon is tidally coupled to Pluto. Thus, Pluto
always shows the same face to Charon just as Charon
always shows the same face to Pluto. It is the only
example of mutual tidal coupling in the solar system.
The result is that for an astronaut standing on Pluto,
Charon is either always visible or never visible.

     The shadows we see on Charon reveal an uneven,
cratered landscape. Like Pluto, Charon is light gray,
although somewhat darker and more even in color than
Pluto, as was known from measurements made from
Earth using the Pluto-Charon eclipses. The very
slightly reddish brown hue of Pluto is missing from
Charon—or at least from Charon's Pluto-facing side,
that is the only side we get to see from the surface of
Pluto. Missing too from Charon is the methane frost
which partially covers Pluto. With Charon's smaller
mass and therefore weaker gravity, whatever methane
ice there was at the surface has evaporated. Perhaps this
in part explains why Charon is less reflective. The
escaping methane has exposed frozen water to view.

     On Earth, we are used to the rising and setting of
the Sun, Moon, and stars as our planet turns. On Pluto,
the Sun rises and sets, if somewhat slowly, but Charon
stays fixed in the sky. It never rises or sets, thanks to
tidal coupling. As Charon revolves once around Pluto
in 6.4 days, Pluto spins once around on its axis in that
same period of time. The result is that Charon hangs
almost stationary in the sky while the Sun and stars
glide slowly past in the background. Because Charon is
so large in the sky, stars are frequently blocked from
view. These stellar occultations are the only eclipses
visible during the 120-year gap between seasons of
solar and lunar eclipses.

     From the vantage point of Earth, Pluto and Charon
pass in front of and behind one another very rarely. The
Earth experiences solar and lunar eclipses at least four
times and sometimes as many as seven times a year.
Because of Pluto's axial tilt and Charon's position over
Pluto's equator, the pair go for almost 120 years
without their shadows ever falling upon one another.
Then, in a period roughly six years long, Charon's orbit
is nearly edge on to Earth and every 6.39-day orbit
Charon makes carries it across the face of Pluto and
then around behind Pluto. The result is an eclipse
frenzy. Serendipitously, that eclipse season began in
1985, soon after Charon was discovered.

     During an eclipse of the Sun on Pluto, Charon
would look like a giant dark hole in the sky, marked
only by the absence of stars. It would be dark but not
black because it would be illuminated by reflected light
from Pluto. The corona—the outer atmosphere of the
Sun, which makes solar eclipses seen from Earth so
beautiful—would be visible only just after the Sun van-
ished and just before it reappeared. At mid-eclipse, the
disk of Charon covers the entire orbit of the Earth. The
corona is far too faint at that distance from the Sun to
peer around the edges of Charon.



The passage states that Charon never sets because of:

A. an eclipse frenzy.
B. stellar occultations.
C. tidal coupling.
D. escaping methane.



The passage asserts that Charon's relationship with Pluto is unique in our solar system in regard to:

F. frequency of eclipses.
G. mutual tidal coupling.
H. synchronous rotation.
J. axial tilt.



The main point of the first paragraph is that:

A. Charon is more similar to Earth's moon than you might expect.
B. Charon is surprisingly similar to Pluto.
C. Charon's closeness to Pluto makes it appear huge from the surface of its planet.
D. in terms of size, the Earth is to Pluto as a billiard ball is to a pea.



As it is defined in the passage, the Sun's corona is:

  I. the Sun's outer atmosphere.
  II. illuminated by reflected light.
  III. reflected light.

F. I only
G. III only
H. I and III only
J. I, II, and III



The long spans of time that elapse between periods of eclipse frenzy on Pluto are the result of:

  I. Pluto's axial tilt.
  II. methane escaping Charon's surface.
  III. Charon's position relative to Pluto's equator.

A. I only
B. III only
C. I and II only
D. I and III only


The passage asserts that one feature of Pluto that is lacking on Charon is:

F. escaping methane.
G. noticeable gravity.
H. a cratered landscape.
J. methane frost.



It can reasonably be deduced from the first paragraph that the number of degrees in the Earth's sky taken up by our Moon is roughly:

A. 0.5 degree.
B. 1.0 degree.
C. 4.0 degrees.
D. 8.0 degrees.



The passage states that the methane ice on Charon evaporated because of that moon's:

  I. smaller mass.
  II. weaker gravity.
  III. axial tilt.

F. II only
G. I and II only
H. I and III only
J. I, II, and III



The passage states that all major satellites in our solar system have in common the fact that they have:

A. axial tilt and somewhat noticeable mutual tidal coupling.
B. closer proximity to their respective planets than our Moon has to Earth.
C. synchronous rotation caused by tidal coupling to their planets.
D. periods of eclipse that are frenzied and also serendipitous.



The passage suggests that the discovery of Charon was made even more interesting for scientists because that discovery coincided with:

F. the discovery of the synchronous rotation of satellites.
G. a large number of eclipses occurring on Pluto.
H. the realization that our Moon is identical to Charon.
J. a demonstration of tidal coupling by Earth and its Moon.

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