The Beginnings of Radar Astronomy
1 In 1946, scientists associated with the United States Army initiated Project Diana, named after the Roman goddess of the Moon, thereby launching the field of radar astronomy. █ In Project Diana, pulses of radio energy were surged through a specially made antenna aimed at the Moon, traveled at the speed of light to the dusty lunar surface, bounced off, and made the return trip to Earth, where they were detected with the same antenna, creating the first radar contact with a celestial body. █ The experiment was conducted to explore the use of the Moon as a passive reflector to beam radio signals toward different parts of Earth. █
2 Some thirty years after the first radar contact with the Moon, scientists used the largest circular radar antenna on Earth, at Arecibo, Puerto Rico, to bounce radio signals from some moons of Jupiter, which are about the same size as our Moon, but about seventeen hundred times farther away. █ Optical cameras were first used to photograph planetary objects, but radar astronomy has proved to be a valuable tool for
planetary scientists probing the nature of the surfaces of planets and their moons. Radar instruments have become an important component of several interplanetary spacecraft because they are configured to produce a map of the surface over which they are passing. These radar maps show properties of surface features not detectable in the ordinary light used by optical cameras. Furthermore, radar passes through clouds and hazes that are otherwise impenetrable with ordinary cameras. Scientists used radar on the Magellan spacecraft, which orbited Venus from 1990 to 1994, to map the entire surface of the planet, although the planet’s cloudy atmosphere is opaque to visible light .
3 From Earth, the Arecibo dish and other antennas have been used to make radar maps of the nearby planets Mercury and Venus, as well as the Moon, although these efforts have been constrained by the limited aspects of these bodies as seen from our planet, a view less complete than that from an orbit around the body itself. Both the Moon and Mercury have distinctive radar “signatures,” that is, the particular way their surfaces reflect radio frequency waves, and these signatures are different for different parts of the surface. Solid lava flows from volcanoes reflect radio waves differently than dusty plains, for example. When first exploring the radio signatures of various regions on the surface of Mercury, scientists found that the surface near the planet’s north pole reflected the radar signal much better than the other areas of the planet. Such high radar reflectivity had previously been seen only in similar observations of regions on Mars known to be icy and also on the icy moons of the outer planets (Jupiter, Saturn, Uranus, and Neptune). These observations led to the astonishing conclusion that in the polar regions of the planet nearest the Sun, ice is present in the permanently shaded walls of craters and other steeply inclined topography (surface features). Mercury’s surface temperature near the equator at high noon is about 425 degrees Celsius, while in the depth of night on the side facing away from the Sun, the temperature is about −173 degrees Celsius. This range occurs largely because there is no atmosphere to retain and distribute the daytime heat. Also, because Mercury’s rotation period is very slow, the days and nights are very long, taking 176 Earth days to fully rotate.
4 While Mercury’s icy polar regions were first detected from Earth-based radar observations, a close-range study was made with the Messenger spacecraft, which orbited Mercury between 2011 and 2015; it was intentionally crashed into the planet on April 30, 2015, after a highly successful mission of mapping the surface and studying the magnetic field. Messenger carried a mapping radar instrument that pinpointed the craters and surrounding areas at the planet’s poles where the water ice is preserved in places of permanent shadow.
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1 In 1946, scientists associated with the United States Army initiated Project Diana, named after the Roman goddess of the Moon, thereby launching the field of radar astronomy. █ In Project Diana, pulses of radio energy were surged through a specially made antenna aimed at the Moon, traveled at the speed of light to the dusty lunar surface, bounced off, and made the return trip to Earth, where they were detected with the same antenna, creating the first radar contact with a celestial body. █ The experiment was conducted to explore the use of the Moon as a passive reflector to beam radio signals toward different parts of Earth. █
According to paragraph 1, which TWO of the following were true of Project Diana? To receive credit, you must select TWO answer choices.
It established the first radar contact with the Moon.
It used an antenna to beam radio signals to the Moon’s surface.
It beamed radio signals from different parts of Earth to the Moon.
It used information about the Moon to explore other celestial bodies.
2
2 Some thirty years after the first radar contact with the Moon, scientists used the largest circular radar antenna on Earth, at Arecibo, Puerto Rico, to bounce radio signals from some moons of Jupiter, which are about the same size as our Moon, but about seventeen hundred times farther away. █ Optical cameras were first used to photograph planetary objects, but radar astronomy has proved to be a valuable tool for
planetary scientists probing the nature of the surfaces of planets and their moons. Radar instruments have become an important component of several interplanetary spacecraft because they are configured to produce a map of the surface over which they are passing. These radar maps show properties of surface features not detectable in the ordinary light used by optical cameras. Furthermore, radar passes through clouds and hazes that are otherwise impenetrable with ordinary cameras. Scientists used radar on the Magellan spacecraft, which orbited Venus from 1990 to 1994, to map the entire surface of the planet, although the planet’s cloudy atmosphere is opaque to visible light .
In paragraph 2, why does the author mention that Venus’ “ cloudy atmosphere is opaque to visible light ”?
To point out the difference between Venus’ surface and the surfaces of some of Jupiter’s moons
To suggest that the map of Venus’ surface produced by the Magellan spacecraft was not very accurate
To emphasize the significance of using radar instruments on interplanetary spacecraft to map the surfaces of planets
To demonstrate the improvements made to radar instruments in the 1990s
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2 Some thirty years after the first radar contact with the Moon, scientists used the largest circular radar antenna on Earth, at Arecibo, Puerto Rico, to bounce radio signals from some moons of Jupiter, which are about the same size as our Moon, but about seventeen hundred times farther away. █ Optical cameras were first used to photograph planetary objects, but radar astronomy has proved to be a valuable tool for
planetary scientists probing the nature of the surfaces of planets and their moons. Radar instruments have become an important component of several interplanetary spacecraft because they are configured to produce a map of the surface over which they are passing. These radar maps show properties of surface features not detectable in the ordinary light used by optical cameras. Furthermore, radar passes through clouds and hazes that are otherwise impenetrable with ordinary cameras. Scientists used radar on the Magellan spacecraft, which orbited Venus from 1990 to 1994, to map the entire surface of the planet, although the planet’s cloudy atmosphere is opaque to visible light .
According to paragraph 2, radar instruments are superior to optical cameras for which TWO of the following reasons? To receive credit, you must select TWO answer choices.
They can view planetary surfaces from a greater distance than optical cameras can.
They can be placed on interplanetary spacecraft.
They can detect surface features that optical cameras cannot.
They can produce maps of surfaces regardless of weather conditions.
4
3 From Earth, the Arecibo dish and other antennas have been used to make radar maps of the nearby planets Mercury and Venus, as well as the Moon, although these efforts have been constrained by the limited aspects of these bodies as seen from our planet, a view less complete than that from an orbit around the body itself. Both the Moon and Mercury have distinctive radar “signatures,” that is, the particular way their surfaces reflect radio frequency waves, and these signatures are different for different parts of the surface. Solid lava flows from volcanoes reflect radio waves differently than dusty plains, for example. When first exploring the radio signatures of various regions on the surface of Mercury, scientists found that the surface near the planet’s north pole reflected the radar signal much better than the other areas of the planet. Such high radar reflectivity had previously been seen only in similar observations of regions on Mars known to be icy and also on the icy moons of the outer planets (Jupiter, Saturn, Uranus, and Neptune). These observations led to the astonishing conclusion that in the polar regions of the planet nearest the Sun, ice is present in the permanently shaded walls of craters and other steeply inclined topography (surface features). Mercury’s surface temperature near the equator at high noon is about 425 degrees Celsius, while in the depth of night on the side facing away from the Sun, the temperature is about −173 degrees Celsius. This range occurs largely because there is no atmosphere to retain and distribute the daytime heat. Also, because Mercury’s rotation period is very slow, the days and nights are very long, taking 176 Earth days to fully rotate.
The word “ steeply ” in the passage is closest in meaning to
sharply
similarly
naturally
generally
5
3 From Earth, the Arecibo dish and other antennas have been used to make radar maps of the nearby planets Mercury and Venus, as well as the Moon, although these efforts have been constrained by the limited aspects of these bodies as seen from our planet, a view less complete than that from an orbit around the body itself. Both the Moon and Mercury have distinctive radar “signatures,” that is, the particular way their surfaces reflect radio frequency waves, and these signatures are different for different parts of the surface. Solid lava flows from volcanoes reflect radio waves differently than dusty plains, for example. When first exploring the radio signatures of various regions on the surface of Mercury, scientists found that the surface near the planet’s north pole reflected the radar signal much better than the other areas of the planet. Such high radar reflectivity had previously been seen only in similar observations of regions on Mars known to be icy and also on the icy moons of the outer planets (Jupiter, Saturn, Uranus, and Neptune). These observations led to the astonishing conclusion that in the polar regions of the planet nearest the Sun, ice is present in the permanently shaded walls of craters and other steeply inclined topography (surface features). Mercury’s surface temperature near the equator at high noon is about 425 degrees Celsius, while in the depth of night on the side facing away from the Sun, the temperature is about −173 degrees Celsius. This range occurs largely because there is no atmosphere to retain and distribute the daytime heat. Also, because Mercury’s rotation period is very slow, the days and nights are very long, taking 176 Earth days to fully rotate.
Which of the following can be inferred from paragraph 3 about radar signatures?
Radar signatures of the Moon and Mercury are easier to detect than those of other planetary bodies.
Radar signatures are unique to each planet.
Radar signatures vary according to surface conditions.
Radar signatures can be used to determine the temperature range of a planet.
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3 From Earth, the Arecibo dish and other antennas have been used to make radar maps of the nearby planets Mercury and Venus, as well as the Moon, although these efforts have been constrained by the limited aspects of these bodies as seen from our planet, a view less complete than that from an orbit around the body itself. Both the Moon and Mercury have distinctive radar “signatures,” that is, the particular way their surfaces reflect radio frequency waves, and these signatures are different for different parts of the surface. Solid lava flows from volcanoes reflect radio waves differently than dusty plains, for example. When first exploring the radio signatures of various regions on the surface of Mercury, scientists found that the surface near the planet’s north pole reflected the radar signal much better than the other areas of the planet. Such high radar reflectivity had previously been seen only in similar observations of regions on Mars known to be icy and also on the icy moons of the outer planets (Jupiter, Saturn, Uranus, and Neptune). These observations led to the astonishing conclusion that in the polar regions of the planet nearest the Sun, ice is present in the permanently shaded walls of craters and other steeply inclined topography (surface features). Mercury’s surface temperature near the equator at high noon is about 425 degrees Celsius, while in the depth of night on the side facing away from the Sun, the temperature is about −173 degrees Celsius. This range occurs largely because there is no atmosphere to retain and distribute the daytime heat. Also, because Mercury’s rotation period is very slow, the days and nights are very long, taking 176 Earth days to fully rotate.
According to paragraph 3, which of the following was surprising to scientists first exploring the radio signatures of various regions on the surface of Mercury?
The fact that they found different signatures in different areas
The high radar signal reflectivity of the north pole surface
The high surface temperature near the equator at high noon
The planet’s lack of an atmosphere to retain and distribute heat
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3 From Earth, the Arecibo dish and other antennas have been used to make radar maps of the nearby planets Mercury and Venus, as well as the Moon, although these efforts have been constrained by the limited aspects of these bodies as seen from our planet, a view less complete than that from an orbit around the body itself. Both the Moon and Mercury have distinctive radar “signatures,” that is, the particular way their surfaces reflect radio frequency waves, and these signatures are different for different parts of the surface. Solid lava flows from volcanoes reflect radio waves differently than dusty plains, for example. When first exploring the radio signatures of various regions on the surface of Mercury, scientists found that the surface near the planet’s north pole reflected the radar signal much better than the other areas of the planet. Such high radar reflectivity had previously been seen only in similar observations of regions on Mars known to be icy and also on the icy moons of the outer planets (Jupiter, Saturn, Uranus, and Neptune). These observations led to the astonishing conclusion that in the polar regions of the planet nearest the Sun, ice is present in the permanently shaded walls of craters and other steeply inclined topography (surface features). Mercury’s surface temperature near the equator at high noon is about 425 degrees Celsius, while in the depth of night on the side facing away from the Sun, the temperature is about −173 degrees Celsius. This range occurs largely because there is no atmosphere to retain and distribute the daytime heat. Also, because Mercury’s rotation period is very slow, the days and nights are very long, taking 176 Earth days to fully rotate.
According to paragraph 3, which of the following suggested to scientists that ice was present in Mercury’s north polar regions?
Similarities between the reflectivity of Mercury’s north polar regions and some regions of Mars
The presence of craters with shaded walls
Mercury’s night temperature on the side facing away from the Sun
Mercury’s very slow rotation period
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4 While Mercury’s icy polar regions were first detected from Earth-based radar observations, a close-range study was made with the Messenger spacecraft, which orbited Mercury between 2011 and 2015; it was intentionally crashed into the planet on April 30, 2015, after a highly successful mission of mapping the surface and studying the magnetic field. Messenger carried a mapping radar instrument that pinpointed the craters and surrounding areas at the planet’s poles where the water ice is preserved in places of permanent shadow.
The word “ preserved ” in the passage is closest in meaning to
formed
hidden
seen
maintained
9
1 In 1946, scientists associated with the United States Army initiated Project Diana, named after the Roman goddess of the Moon, thereby launching the field of radar astronomy. █ In Project Diana, pulses of radio energy were surged through a specially made antenna aimed at the Moon, traveled at the speed of light to the dusty lunar surface, bounced off, and made the return trip to Earth, where they were detected with the same antenna, creating the first radar contact with a celestial body. █ The experiment was conducted to explore the use of the Moon as a passive reflector to beam radio signals toward different parts of Earth. █
2 Some thirty years after the first radar contact with the Moon, scientists used the largest circular radar antenna on Earth, at Arecibo, Puerto Rico, to bounce radio signals from some moons of Jupiter, which are about the same size as our Moon, but about seventeen hundred times farther away. █ Optical cameras were first used to photograph planetary objects, but radar astronomy has proved to be a valuable tool for
planetary scientists probing the nature of the surfaces of planets and their moons. Radar instruments have become an important component of several interplanetary spacecraft because they are configured to produce a map of the surface over which they are passing. These radar maps show properties of surface features not detectable in the ordinary light used by optical cameras. Furthermore, radar passes through clouds and hazes that are otherwise impenetrable with ordinary cameras. Scientists used radar on the Magellan spacecraft, which orbited Venus from 1990 to 1994, to map the entire surface of the planet, although the planet’s cloudy atmosphere is opaque to visible light .
The United States military successfully used the moonbounce communication technique in 1960 to establish a link between Hawaii and Washington, D.C.
Where would the sentence best fit? Click on a square [█] to add the sentence to the passage.
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Project Diana launched the field of radar astronomy in 1946.
A)Scientists using special antennas on Earth conducted early research in radar astronomy by bouncing radio signals first from the Moon and years later from some moons of Jupiter back to Earth.
B)Earth-based antennas were used for creating complete maps of nearby bodies such as Mercury, Venus, and the Moon, but it was impossible to reach all areas of more distant bodies.
C)The missions in radar astronomy conducted with Mercury were successful largely because the planet’s slow rotation helped create more favorable atmospheric conditions for study.
D)Without the limitations of Earth-based antennas and optical cameras, radar instruments on spacecraft in orbit around planetary bodies were able to completely map their surfaces.
E)A comparison of the radar signatures of the Moon and Mercury with those of Mars and the moons of Jupiter. Saturn. Uranus, and Neptune revealed the presence of ice in areas of the bodies nearest the Sun.
F)Earth-based radar observations detected Mercury’s icy polar regions, and the Messenger spacecraft mapped the surface, indicating the areas of the poles where the ice is located.
