Chapter 28 Assessmentp. 772 - 773

1. What is a planet’s backward motion in the sky called?b. retrograde motion

2. What point in a planet’s orbit is closest to the Sun?d. perihelion

3. What model of our solar system did Copernicus propose?a. a heliocentric model

4. A planet’s average distance from the Sun is also what part of the orbital ellipse?

a. summer solstice

5. Which of the following provides evidence that the Earth is rotating?b. The plane of a Foucault pendulum, appears to shift its orientation.

6. Which of the following is in correct order?b. waxing gibbous, full moon, waning gibbous, third quarter

7. List the various forms of electromagnetic radiation according to wavelength, from shortest to longest.

In order of shortest to longest wavelength, the forms of electromagnetic radiation are: gamma rays, X rays, ultraviolet radiation, infrared radiation, microwaves, and radio waves.

8. Why must some telescopes be launched into space? Recall that the ultimate goal of telescopes, and of astronomers, is to be

able to observe and analyze all forms of electromagnetic radiation, not solely visible light, which is what the human eye perceives. The Earth’s atmosphere blocks either entirely, or at least in part, other forms of electromagnetic radiation, such as infrared and ultraviolet radiation, gamma rays, etc. When the atmosphere allows such wavelengths past, the images produced are blurred. Thus, telescopes must be launched into space to perceive these radiations.

9. List the types of shadows as well as the types of eclipses that will be seen by an observer on the unlit side of Earth.

The first diagram (top) illustrates a total lunar eclipse. Where the Moon enters the Earth’s umbra in its entirety. An observer on Earth will witness a reddish colored moon, which occurs as a result of the refracting effect of the Earth’s atmosphere upon sunlight that in the end reaches the Moon.

The second diagram (bottom) illustrates a partial lunar eclipse, where only half the Moon enters the Earth’s umbra. In such a situation, half the Moon (the one in the penumbra) will be slightly more visible than the other half (the one in the umbra).

10. What is electromagnetic radiation? Electromagnetic radiation is a type of radiation, which is emitted by

celestial objects. It is comprised of electric and magnetic radiation, and includes several different types, such as infrared and ultraviolet radiation, radio waves, microwaves, X rays, and gamma rays.

11. How was the lunar regolith formed?The lunar regolith was a layer of loose, ground-up rock that formed

around 3.8 and 4.6 billion years ago, early in the Moon’s history, during the formation of one of its most prominent features – the highlands. During the first 8000 million years of the Moon’s history, the celestial object was heavily bombarded, and impact craters began to appear as a result. The heavy bombardment caused in the breaking and heating of rocks on the surface of the Moon, which in turn caused the formation of a layer of regolith – a layer of loose, ground-up rock. The regolith formed averages several meters in thickness; although it varies considerably, depending on location.

12. Describe how a lunar month is defined. How long is it? A lunar month is otherwise the term for a complete cycle of the

Moon’s phases, and it takes about 29. 5 days, this is noteworthy as it is longer than the 27.3 days it takes for a lunar revolution.

13. Of all types of electromagnetic radiation, which can the human eye detect?

The humane ye only possess the ability of perceiving visible light.

14. How did the mountain ranges around the maria on the Moon form? Around 3.1 – 3.8 billion years ago in lunar history, during the

formation of its maria, the previous bombardment caused lava to well up to the Moon’s surface from its interior. The lava filled up all the impact basins caused by the impact craters, save for the rims of these basins. These rims later became the mountain ranges characteristic of lunar maria.

15. Why are the temperature fluctuations on the surface of the Moon so extreme compared to those on Earth?

The extreme lunar temperature fluctuations are due to the absence of a lunar atmosphere. In presence of the Sun, the lunar surface may be heated up to around 400 K, where as it may cool down to -173 K in the Sun’s absence.

16. What are the Moon’s positions relative to the Sun and Earth when we observe a full moon and a new moon?

In its new moon phase, the Moon is between the Sun and the Earth. In a full moon stage, the Moon is “behind” or “to the left” of both Earth and the Sun.

17. Why does the Sun’s altitude in the sky change throughout the year? The Sun’s altitude changes in the sky as a result of Earth’s axial tilt,

and its motion around the Sun. This is the reason why the Sun appears higher in the sky during the northern hemisphere’s summer than during its winter.

18. If the Moon rotated twice on its axis for every one time it orbited Earth, would it be in synchronous rotation? Explain.

No, it would not. Recall that synchronous rotation is the state at which orbital and rotational periods are equal. The rotational period of the Moon (27.3 days) equals the time it takes for it to spin around its axis (also 27. 3 days). If it were to rotate twice on its axis every time it orbited Earth, it would only take 13.65 days to complete that rotation – half of its orbital period. Because of the difference in its orbital and rotational periods, it would no longer be in synchronous rotation.

19. Suppose the Moon’s orbital plane were exactly aligned with Earth’s orbital plane. How often would eclipses occur?

20. Why is it best to get away from the city lights to view the nighttime sky? In cities, light pollution is present. This pollution, caused by over

illumination in urban areas and buildings, reduces the contrast between the stars in the sky, and the sky itself, making it extremely more difficult to see the faintest of stars.

21. How would Earth’s surface look if Earth did not have an atmosphere? Take, for example, the inner planet, Venus. Its densely clouded

atmosphere prevents us from seeing many of its surface features from Earth. The Earth’s atmosphere, in contrast, is not as cloudy as that of Venus, and thus, it is possible to see its most prominent features (e.g. oceans, continents).

22. Why did one-half of the Moon’s surface remain hidden from human sight until the era of space probes, which started in 1959?

This is because of the Moon’s synchronous rotation – it rotates on its axis at the same rate it goes around its orbit. Thus, people on Earth always saw the same side of the Moon in the night sky. Space probes

allowed astronomers to go beyond this side of the Moon to its far side, which we never see.

23. When observers on Earth can see a total lunar eclipse, what kind of eclipse can be seen by an observer on the Moon?

An observer on the Moon will see a total solar eclipse. This is because in a lunar eclipse, the Earth ends up being in front of the Sun to an observer on the Moon; thus, a solar eclipse would be witnessed, as the Earth would block out the Sun much the same way the Moon would in a solar eclipse witnessed from Earth.

24. In some maria, there are craters. Which are younger, the maria or the craters?

The craters are younger than the maria. The maria formed between 3.1 – 3.8 billion years ago, after the initial 800 million-year-long period of bombardment, which was what resulted in these impact craters.

25. How would the topography of the Moon be different if the Moon had an atmosphere?

Once again, take the inner planet Venus as an example. The densely clouded atmosphere of the planet prevents us from being able to see many of its ruface features without actually touching down on its surface. Thus, if the Moon had an atmosphere, its features would be less visible, blurred, or not visible at all (depending on the cloudiness in its atmosphere [whether it is dense or not]).