Question 1 refers to the following information.
Modern astronomy is said to have started with Nicolaus Copernicus in the sixteenth century. He pointed out that the Sun, not Earth, was the central body in the solar system. This knowledge gave later scientists, like Tycho Brahe, a basis for describing the motions of the bodies in the system.
Johannes Kepler studied Brahe’s data and formulated three laws of planetary motion:
Planetary orbits are elliptical.
The closer a planet is to the Sun, the faster it moves around the Sun.
The size of a planet's orbit is related to the amount of time it takes to orbit the Sun. The larger the orbit, the longer one full revolution takes.
Kepler did not try to explain the forces that acted on planets. In the seventeenth century, Isaac Newton explained why the planets move as they do by writing his laws of motion and gravitation.
Questions 2 through 4 refer to the following information.
Returning a spacecraft to Earth intact is a difficult operation. How can the craft be slowed down for landing? The ideal method would be to use braking rockets similar to those used to launch the craft. Unfortunately, this type of braking system would require putting a gigantic rocket into orbit simply to land the spaceship.
All spacecraft so far have used an aerodynamic system—one that uses Earth’s atmosphere as a brake. This method relies on the physical law that an object will come to rest only when its kinetic energy—energy of motion—is converted to some other form of energy, such as light, sound, or heat.
A spacecraft moving 18,000 miles per hour contains an enormous amount of kinetic energy. This energy is converted mainly into heat as the craft plows back into Earth’s atmosphere, and friction with the air begins to slow it down. Space engineers developed several ways to remove this heat so that the spacecraft would not burn up: (1) A heat shield in front of the craft heats up to several hundred degrees Celsius and radiates heat back into the air. (2) Part of the outside shell of the craft is burned off as the shell absorbs the heat. (3) The surface of the craft heats up the air in contact with it, leaving behind a stream of hot air.
Although the aerodynamic landing system is not ideal, it will be used for a long time because it is less costly and more fuel-efficient than other braking systems.
Question 5 refers to the following information.
A meteor is usually a small rock from space that enters Earth’s atmosphere and burns up, causing a bright streak of light across the sky. The graph shows the number of meteors a group of amateur astronomers observed during one night.
Questions 7 and 8 refer to the following information.
It may sound odd, but scientists can tell what gases surround a planet by looking for light that isn’t there! The visible light from the Sun is a mixture of wavelengths. It produces a continuous band of colors from red and orange through yellow and green and on to blue and violet. Scientists use instruments called spectrographs to study the light from planets. The spectroscope separates white light into the colors that make up the light. However, there are usually dark lines in the spectrum of a planet. The dark lines show which wavelengths of light are absorbed by the gases in a planet’s atmosphere. A spectrum with these identifying dark lines is called an absorption spectra. Each element produces a specific, unique, pattern of dark lines. Below are a continuous spectrum and an absorption spectrum for hydrogen.
The hydrogen spectra has dark lines at the violet end of the spectrum at 4.1 × 10-5 cm, 4.3, × 10-5 cm, a blue-green line at 4.8 × 10-5 cm and a line in the red part of the spectrum at 6.6 × 10-5 cm.
Questions 9 and 10 refer to the following information.
Space may still be vast, but it can no longer be called "empty." At the beginning of this century, space was crowded with junk and garbage left behind by forty years of space exploration. Items as large as abandoned satellites and as small as nuts and bolts have been dumped into space. The biggest problem is that this junk is moving—it travels at speeds up to 7.5 kilometers per second, fast enough that a collision can vaporize metal. Even a 0.5-centimeter paint flake could punch a fist-sized hole in the shuttle’s crew compartment or wing.
Radar systems on the ground can detect debris larger than a volleyball. When it looks as if debris might collide with the space station or other occupied satellite, astronauts maneuver their ships to avoid collision. While researchers design ways to remove the junk from space, the international community is currently taking steps to send less junk into space in the first place.