7th Grade Science Chapter 20 Answers

  1. AU represents the average distance between the Earth and the Sun as it orbits the Sun. p538
  2. The distance between the stars is measured in Light-years.
  3. The 2 groups of planets are called the inner planets and the outer planets. P539
  4. The differences between the inner and outer planets include their size, the materials they are made of and the inner planets are more closely spaced than the outer planets.
  5. The inner planets are called the terrestrial planets.
  6. The inner planets are as follows: Sun (not a planet), Mercury, Venus, Earth and Mars
  7. The inner planets are small, dense and rocky.
  8. The outer planets are mostly made of gases, with the exception of Pluto.
  9. The time it takes for an object to rotate once on its axis is its Period of Rotation
  10. A year is the amount of time it takes for a planet to go around the sun once.
  11. The motion of a body as it orbits another body in space is its Revolution
  12. The time it takes an object to revolve around the sun is its Period of Revolution
  13. Prograde rotation is revolution or spin in a counterclockwise direction. Retrograde rotation is a revolution or spin in a clockwise direction. The Earth has a Prograde Rotation, along with 5 of the other planets. Venus, Uranus, and Pluto all have a Retrograde Rotation.
  14. Earth’s twin is Venus p540-
  15. Earth Venus are similar in size, mass & density. However, Venus is much hotter, the sun rises in the west sets in the east the two rotate in opposite directions. Venus is Retrograde and Earth is Prograde.
  16. Venus has an average temperature of 464 degrees Celsius, making it the hottest planet. This is due to the Greenhouse Effect – This is where the CO2 in the atmosphere traps the thermal energy from the sunlight.
  17. Earth is able to sustain life because it is just the right distance from the sun. The temperature is not too hot and not too cold, giving the Earth the ability for water to exist in a liquid form. P541
  18. Mars is the Red Planet p542
  19. Our solar system consists of 8 planets and Pluto which is classified by most scientists as a Dwarf Planet.
  20. The pressure on the surface of Mars is so low that water simply boils away, making life unable to exist.
  21. The outer planets are called the Gas Giants, except Pluto p544
  22. The outer planets are very large, made of gases, and have no known solid surface.
  23. The order of the outer planets: Jupiter, Saturn, Uranus, Neptune, and Pluto.
  24. The gas giants
  25. Jupiter’s Great Red Spot is a long-lasting storm system. This spot is = to 1 ½ times that of Earth.
  26. False: Jupiter Saturn actually radiate more energy than they receive from the sun. For Jupiter it’s because energy is continuously moving between its layers within the atmosphere interior. For Saturn scientists believe the extra energy comes from helium raining out of the atmosphere sinking to the core.
  27. Saturn is the 2nd largest planet with the largest set of rings. P 545
  28. Yes, all of the gas giants have rings, although Saturn’s are the largest.
  29. Uranus is tipped over on its side, the axis of rotation is tilted almost 90o, and it lies almost in the plane of its orbit. Scientists believe this may have been the result of a hit from a massive object early on. P546
  30. Neptune’s interior releases energy to its out layers. This allows warm gases to rise and the cool gases sink, setting up the wind patterns in the atmosphere. P 547
  31. Most scientists classify Pluto as a dwarf planet. It is the smallest of “planets” and half the size of Mercury.
  32. Pluto is actually made of rock and ice, not gases. P 548
  33. Satellites are natural or artificial bodies that revolve around larger bodies like planets. P 549
  34. moons p 549
  35. No, Mercury and Venus do not have natural satellites.
  36. We call the Earth’s moon Luna.
  37. Scientist’s knowthe surfaces of bodies that have no atmosphere, like our moon, preserve a record of almost all the impacts they have had with other objects. P549
  38. Scientists believe the Earth’s moonor “Luna” and the Solar System are approximately 4.6 billion years old. Scientists have examined lunar rocks brought back to Earth & noticed that they have not changed since they were formed. From these rocks scientists were able to calculate the age of the moon and our solar system. Additionally, we know that surfaces of bodies that have no atmosphere preserve a record of almost all impacts. By combining this knowledge scientists can calculate the age of other surfaces. P 549
  39. The Earth’s moon is believed to have formed as a result of a Mars-sized object colliding with the Earth while the Earth was still forming, about 4.6 billion years ago. Scientists believe that the blast was so significant that a giant piece of the Earth’s mantle was blasted into orbit around the Earth. P550
  40. Our moon has a lower density than the Earth, therefore it has a lower percentage of heavy elements. Additionally, the composition of the lunar rocks that have been collected, suggest that the moon is similar to that of the Earth’s mantle, but also has part of the object that collided with the Earth. P 549
  41. Phases refer to the different appearances of the moon due to its changing position. The moon has a number of phases, all due to the amount of sunlight on the side of the moon that faces the Earth. P 551
  42. We see the different appearances (phases) of the moon due to the moons changing position with respect to the Earth and the sun. As the moon revolves around the Earth, the amount of sunlight on the side of the moon that faces the Earth changes. P 551
  43. Waxing means the amount of sunlight we see on the moon is getting larger leading to a Full Moon. Waningis the amount of sunlight we see on the moon is growing smaller leading to a New Moon. p 551
  44. An eclipse occurs when the shadow of one celestial body falls on another. A lunar eclipse happens when the Earth comes between the sun and the moon. As a result the shadow of the Earth falls on the moon. A solar eclipse happens when the moon comes between the Earth and the sun and the shadow of the moon falls on the Earth. P 552
  45. An annular eclipse is when a solar eclipse occurs during which the outer ring of the sun can be seen around the moon.P 552
  46. The moon’s orbit around the Earth is tilted, about 5o, with respect to the orbit of the Earth around the sun. This tilt causes the moon to fall out of the Earth’s shadow for most full moons. The tilt also causes the Earth to be out of the moons shadow for most of the new moons. P 553
  47. Solar eclipse occurs during a New Moon.
  48. We always see the same side of the moon because the period of rotation for the moon is the same as its period of revolution. Meaning, the time it takes to rotates one time on its axis is equal to the time it takes the moon to revolve around the Earth, leaving us to see the same side of the moon.
  49. Yes, all of the outer planets have multiple moons. P 554 & 556
  50. Jupiter has 28 moons total. Io is one of its 4 largest and is the most volcanically active natural satellite in the solar system. P544
  51. Scientists study Titan because the atmosphere on the moon now is similar to the atmosphere that the Earth may have had before life began forming. P 555
  52. True, Triton does revolve in a retrograde, or backward orbit. P 556
  53. A comet is a small body of ice, rock, and cosmic dust loosely packed together. P 557
  54. Comets consist of a nucleus (solid center), ion tail (electrically charged particles called ions), a dust tail.
  55. All comets orbitin an ellipse or a stretched out circle. P 558
  56. The Oort cloud is a spherical region that surrounds our solar system. Scientists believe this cloud is the origin to most comets. P 558
  57. The Kuiper belt is another region recently discovered where comets exist. It is outside the orbit of Neptune.
  58. Asteroids are small, rocky bodies in orbit around the sun. P 559
  59. The asteroid belt is the wide region that orbits the sun located between the orbits of Mars and Jupiter.
  60. No, the position of the asteroid in the belt determines its composition. The outermost region is dark reddish brown indicating rich organic material. Closer to the sun they are dark gray, indicating carbon and the innermost asteroids are light gray and are stony or metallic in composition. P 559
  61. A meteoroid is a small, rocky body orbiting the sun (meteoroid = out in space!)
  62. A meteor is the bright streak of light that is caused when a meteoroid or comet dust burns up in the Earth’s atmosphere. (meteor = atmosphere)
  63. A meteorite is the meteoroid that strikes the Earths surface. (meteorite = Earth’s surface).
  64. A meteor shower occurs when the Earth passes through the dusty debris left behind in the orbit of a comet.
  65. Meteorites are composed of different materials. The three major types are stony, metallic, and stony-iron.
  66. They use these to study the solar system and its early beginnings.
  67. So we can learn about other planets and our solar system yesterday, today and into the future. Scientists try to predict when and how often they may occur. Powerful ones may occur every few thousand years, but a destructive one may be once every 30-50 million years.