2. A star shines when energy from nuclear reactions occurring in its core makes it to the star’s surface.

3. An astronomical unit is the average distance between Earth and the Sun (~150 000 000 km).

4. A light-year is the distance travelled by light in one year.

5. There are four different types of galaxies: spiral, barred spiral, elliptical, and irregular

6. Students’ sketches should look like Figure 7.16 on student book page 269. At its widest point the galaxy is about 100 000 ly across and the distance through the galactic bulge is 2000 ly.

7. More than 90% of the mass of the universe is thought to be made up of dark matter.

8. Two pieces of evidence that support the Big Bang theory of the formation of the universe: (i) the universe is expanding, as shown by all galaxies moving away from each other; (ii) cosmic background radiation, believed to be the afterglow of the initial moments of the formation of the universe, has been mapped.

9. Stars are “born” in nebulas.

10. Students’ sketches should look like Figure 8.4 student book page 296.

11. To cause a high-mass star to turn into a supernova, the star must first run out of fuel, which then causes it to collapse in on itself very rapidly, resulting in a large explosion.

12. A neutron star is noted for being made of the densest material known.

14. Two ways that the Sun’s energy interacts with Earth’s atmosphere:

(i) the Sun’s radiation heats Earth’s atmosphere; (ii) solar storms send waves of high-energy particles towards Earth, causing auroras and sometimes interfering with electronic equipment.

15. The temperature of sunspots is lower than the rest of the photosphere because magnetic fields around a sunspot slow convection and prevent the plasma from mixing. This, in turn, lowers the temperature.

16. The aurora borealis is caused when high-energy particles from the Sun interact with Earth’s magnetic field.

17. According to the theory of how the solar system formed, a cloud of gas and dust began spinning. Most of the material accumulated in the centre, eventually contracting into a body called the Sun. The leftover debris continued spinning and contracting in orbit around the Sun and eventually formed the planets.

18. (a) The image shows a comet and its tail.

(b) Energy from the Sun causes materials on the comet to effervesce and the solar winds push this material away from the Sun, creating the appearance of a tail.

19. Because Earth is rotating on its axis in a west-to-east direction, from the perspective of someone on Earth’s surface, it appears that the Sun is rising in the east (though the Sun is not moving, only Earth is).

20. Both the rotation and revolution of Earth are part of what causes the seasons. Earth rotates at a fixed angle as it revolves around the Sun. Seasons result because of the angle of Earth’s axis. When the northern hemisphere is tilted towards the Sun we experience summer, and when the northern hemisphere is titled away from the Sun, we experience winter.

21. (a) Students’ sketches should look like the full phase shown in Figure 8.35 of student book page 326. The Sun is to the right of the illustration.

(b) Students’ sketches should look like the new phase shown in Figure 8.35 of student book page 326. The Sun is to the right of the illustration.

22. Early people studied space to mark time, predict seasons, navigate, monitor migration patterns for hunting and fishing, and mark annual celebrations.

23. (a) Summer solstice is the day in the year with the greatest number of daylight hours.

(b) Winter solstice is the day in the year with fewest number of daylight hours.

(c) Equinox refers to the two days of the year with an equal number of daylight and night hours.

24. Retrograde motion means the apparent reversal of a planet’s direction of motion across the sky relative to a starry backdrop.

25. Saturn has a greater orbital radius than Mars because Saturn lies farther from the Sun than Mars does.

26. Galileo was able to use the early telescope to observe, for the first time, mountains on the Moon, four moons orbiting Jupiter, and Venus in full phase.

27. The shape of planets’ orbits in the solar system is elliptical.

32. (a) The gravitational condition shown in the image is microgravity.

(b) In microgravity, the gravitational forces that act on a mass are greatly reduced. When humans experience this condition, they feel weightless.

(c) Microgravity affects the human body by resulting in loss of bone density, depletion in production of red blood cells, loss of muscle mass, and heart pumping irregularities.

33. Examples of physical hazards that put a spacecraft at risk: cosmic radiation, solar radiation, and natural and human-made space debris.

34. If the Sun were part of a binary star system, we would see two suns from Earth.

35. The star exploded 55 million years ago.

36. Astronomers think that the farthest galaxies we can see may also be the oldest in the universe because the universe has been expanding since its formation, with all galaxies moving away from each other. Therefore, those galaxies farthest away are likely to be the oldest.

37. Students’ answers will vary but should end with Solar System, Milky Way Galaxy, Local Group, Local Cluster, Local Supercluster.

38. (a) Supergiants have high luminosity and lower temperature.

(b) Red giants have medium luminosity and lower temperatures.

(c) White dwarfs have low luminosity and high temperature.

39. (a) Life cycle of a low mass star: birth, red dwarf, white dwarf

(b) Life cycle of a medium mass star: birth, red giant, brown dwarf

40. A coronal mass ejection can affect satellite and telecommunication technologies on Earth.

41. The solar wind contributed to the formation of the solar system by blowing gas and dust away from the nebula in which the Sun formed, far enough away not to fall into the protostar, but to continue orbiting the Sun and forming into a thin disk.

42. The gravitational pull from Jupiter prevents the material in the asteroid belt from forming into a planet.

43. Had Jupiter been a little larger and the pressure in its core greater, nuclear fusion may have been triggered at its centre and the planet might have become a second star in our solar system.

44. The planets in the solar system appear brighter to us than the stars we see in the night sky because the planets (and their reflected light) are located much closer to Earth than any star other than the Sun is.

45. The length of year for a planet depends on how long it takes to make one revolution of the Sun. Each planet lies a different distance from the Sun and therefore its length of year is different.

46. Examples of astronomical phenomena observable from Earth for which early peoples would not have understood the scientific cause include retrograde motion of planets, aurora borealis, solar and lunar eclipses, the changing phases of the Moon, comets, and meteors

49. The statement is not correct (i.e., that humans had no tools to study celestial motion or objects until they invented the telescope) because early people used a whole range of tools and means – including their eyes, sundials, merkhets, astrolabes and cross-staffs – to monitor celestial motion. In addition, great monuments were built to help track the regularly changing positions of celestial objects in the sky.

50. (a) A radio telescope detects and collects radio signals.

(b) Radio telescopes detected cosmic background radiation, providing a vital piece of evidence in support of the Big Bang theory.

54. (a) 9.0 × 1013

(b) 1.5 × 1011

(c) 2.48 × 107

55. (a) (i) Rigel, blue; (ii) the Sun, yellow; (iii) Aldebaran, red

(b) Betelgeuse is 10 000 times brighter than the Sun.

(c) Procyon A is 6000°C.

(d) Yellow stars have a higher surface temperature than red stars.

(e) Red stars such as Betelgeuse can be brighter than other stars because of the red stars’ large size and closeness to Earth.

56. To find the North Star, a person should locate the two stars that make up the outside of the Big Dipper (about the middle of the bear’s back in the constellation Ursa Major) and then follow those “pointers” upwards to find Polaris.

57. Edwin Hubble’s spectral analysis helped show that the farther away a galaxy was, the greater was the red shift in its light spectrum. This suggested that the universe has been expanding since the time it formed.

58. By observing the motion and position of other star-and-planet systems that have been discovered, astronomers are able to see similarities with our own solar system and so verify the theory of how the solar system formed.

59. The Sun has a greater effect on Earth than the Moon does. Although the Moon causes the tides, the Sun provides the radiation that heats Earth’s atmosphere and has allowed life to form on the planet.

60. Space exploration requires an enormous investment of time, resources, and money. The decision to explore space must therefore be made only after the benefits, costs and hazards have been weighed. Questions about whether the investment would be better made improving the lives of people on Earth must be asked, and whether there is a limit to how far humans can expect to go into space.

61. Students’ answers will vary, but possible responses include:

(a) It is advantageous for Canada to contribute space technologies to international projects rather than to pursue space exploration by itself because on its own Canada could not afford on its own the high costs associated with space exploration.

(b) The study of space is so complicated, costly and timeconsuming that scientific knowledge and technologies related to the study of space cannot effectively develop and advance without nations sharing information.

(c) Not sharing scientific knowledge gained from research might be a better decision than sharing it in cases where a country believes the information could be used by other nations for unethical purposes, such as weapons deployment.