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How many known planets are in our solar system?

What dwarf planet was downgraded from planetary status in 2006?

How are the outer planets different from the inner planets aside from their location?

Why does a nebula spin faster as it contracts?

According to the nebular theory, did the planets start forming before or after the Sun ignited?

What happens to the amount of the Suns mass as it burns?

What are sunspots?

What is the solar wind?

How does the rotation of the Sun differ from the rotation of a solid body?

What is the age of the Sun?

Why are the days on Mercury very hot and the nights very cold?

What two planets are evening or morning stars?

Why is Earth called the blue planet?

What gas makes up most of the Martian atmosphere?

What evidence tells us that Mars was at one time wetter than it presently is?

What surface feature do Jupiter and the Sun have in common?

Which move faster: Saturns inner rings or the outer rings?

How tilted is Uranuss axis?

Why is Neptune bluer than Uranus?

Why doesnt the Moon have an atmosphere?

Where is the Sun located when you view a full Moon?

Where are the Sun and the Moon located at the time of a new Moon?

Why dont eclipses occur monthly, or nearly monthly?

How does the Moons rate of rotation about its own axis compare with its rate of revolution around Earth?

Between the orbits of what two planets is the asteroid belt located?

What is the difference between a meteor and a meteorite?

What is the Kuiper belt?

What is the Oort cloud, and what is it noted for?

What is a falling star?

What causes comet tails to point away from the Sun?

Find a Ping-Pong ball on the next clear day when the Moon is out. Hold the Ping-Pong ball with your arm stretched out toward where the Moon is so that the ball overlaps the Moon. Look carefully at how the ball is lit by the Sun. Notice that this is the same way the Moon is lit by the Sun! For an example, see the photograph accompanying Exercise 67. To see the different phases that the Moon would have if it were elsewhere in the sky, move your Ping-Pong ball around. Note as you bring the ball closer to the Sun, the crescent on the ball gets thinner. The same thing happens with the Moon. This activity is a great way of really experiencing the roundness of the Moon.

Simulate the lunar phases. Insert a pencil into a Styrofoam ball. This will be the Moon. Position a lamp (representing the Sun) in another room near the doorway. Hold the ball in front and slightly above yourself. Slowly turn yourself around, keeping the ball in front of you as you move. Observe the patterns of light and shadow on the ball. Relate this to the phases of the Moon.

When viewed from the North Pole, Earth spins counterclockwise, which is toward the east. This means that the stars appear to move in the opposite direction, which is toward the west. This is just like when youre sitting in a train that begins moving eastward. The only way you know that youre moving eastward is because things outside your window give the appearance of moving westward. Just as Earth spins counterclockwise, the Moon revolves around us counterclockwise, though not as fast as we spin. Look where the Moon is located one night at, say, 11:00. Look for the Moon the next night at the same time, and youll see that it has moved eastward (a counterclockwise direction) from where it was on the previous night.

The crescent Moon always points toward the Sun. You can use this fact to estimate your latitude. Down by the equator (0 latitude), the setting crescent Moon lies flat on the horizon, while up close to the North Pole (90 latitude), the crescent Moon stands on its end. Deviations to this can arise because of Earths 23 tilt and because the Moons orbit lies 5 outside the ecliptic. Nonetheless, those who live in Alaska see a crescent Moon that is much more upright than those who live in Hawaii. With this in mind, next time you see the crescent Moon close to the horizon, look carefully at its angle and try correlating that angle to your local latitude.

The planets of our solar system orbit in roughly the same plane, which is the plane of our solar system. We can identify the plane of our solar system in the night sky by noting the positions of the planets, which, from our point of view on Earth, appear in a roughly straight line relative to one another. This straight line, which is a cross-section of our solar system, always intersects with the Sun and often with the position of our Moon. On a clear evening after sunset, several planets can often be seen in the western sky forming a line that points directly toward the Sun. Upon finding this alignment, you are looking directly at the plane of our solar system. Check it out! How might this line look different if viewed from the North Pole versus the equator?

The dates of meteor showers are rather predictable as listed in Table 26.2. How intense the shower might be, however, is still somewhat of a guess. So keep your eye to the nighttime sky for these meteor showers. While doing so, review in your mind the distinctions among meteoroids, meteors, meteorites, and comets. Also notable in our nighttime skies are the lunar eclipses, which can seen by anyone who happens to be on the nighttime side of Earth during the eclipse (assuming skies are clear). Here are the dates for upcoming lunar eclipses viewable in North America. Date Type Dec. 10, 2011 Total Jun. 4, 2012 Partial Apr. 15, 2014 Total Oct. 8, 2014 Total Sep. 28, 2015 Total Jan. 21, 2019 Total

Knowing that the speed of light is 300,000 km/s, show that it takes about 8 min for sunlight to reach Earth.

How many days does sunlight take to travel the 50,000 AU from the Sun to the outer reaches of the Oort cloud?

The light-year is a standard unit of distance used by astronomers. It is the distance light travels in one Earth year. In units of light-years, what is the approximate diameter of our solar system, including the outer reaches of the Oort cloud? (Assume that 1 light-year equals 63,000 AU.)

The nearest star to our Sun is Alpha Centauri, which is about 4.4 light-years away. Assume that it too has an Oort cloud about 1.6 light-years in diameter. Show that there is enough space between us and it to fit about 1.75 solar systems.

If the Sun were the size of a beach ball, Earth would be the size of a green pea 110 m away. Show that the nearest star, Alpha Centauri (4.4 light-years away), would be about 30,000 km distant. (Hint: Find the distance to Alpha Centauri in units of AU.)

Rank these planets in order from longest to shortest year: (a) Mercury, (b) Venus, and (c) Earth.

Rank these planets in order of increasing number of moons: (a) Mars, (b) Venus, and (c) Earth.

Rank in order of increasing average density: (a) Jupiter, (b) Saturn, and (c) Earth.

Rank in order of increasing pressure at the center of each planet: (a) Jupiter, (b) Saturn, and (c) Earth.

Rank in order of decreasing number of people who have seen a: (a) solar eclipse, (b) lunar eclipse, and (c) new Moon.

Rank in order of decreasing number of people who have seen a: (a) solar eclipse, (b) lunar eclipse, and (c) new Moon.

According to nebular theory, what happens to a nebula as it contracts under the force of gravity?

What happens to the shape of a nebula as it contracts and spins faster?

A TV screen is normally light gray when not illuminated. How is the darkness of sunspots similar to the black parts of an image on a TV screen?

When a contracting ball of hot gas spins into a disk shape, it cools. Why?

If Earth didnt spin on its axis but still revolved around the Sun, how long would an Earth day be?

If Earth didnt spin on its axis but still revolved around the Sun, would the Sun set on the eastern or western horizon or not at all?

The greenhouse effect is very pronounced on Venus but doesnt exist on Mercury. Why?

What is the cause of winds on Mars (and also on almost every other planet)?

Why is there so little wind on the surface of Venus?

If Venus were somehow transported into the habitable zone, would conditions once again become favorable for life?

Mercury and Venus are never seen at night straight up toward the top of the sky. Why not?

What is the major difference between the terrestrial and jovian planets?

What does Jupiter have in common with the Sun that the terrestrial planets dont? What differentiates Jupiter from a star?

When it comes to celestial bodies, such as planets and stars, why doesnt a larger size necessarily mean a larger mass?

Why are the seasons on Uranus different from the seasons on any other planet?

Earth rotates much faster than Venus. How does the giant impact theory of the Moon account for this fact?

Why are many craters evident on the surface of the Moon but not on surface of Earth?

Why is there no atmosphere on the Moon? Defend your answer.

Is the fact that we see only one side of the Moon evidence that the Moon spins or that it doesnt spin? Defend your answer.

Photograph (a) shows the Moon partially lit by the Sun. Photograph (b) shows a Ping-Pong ball in sunlight. Compare the positions of the Sun in the sky when each photograph was taken. Do the photos support or refute the claim that they were taken on the same day? Defend your answer.

We always see the same face of the Moon because the rotation of the Moon on its axis matches the rate at which it revolves around Earth. Does it follow that an observer on the Moon always sees the same face of Earth?

If we never see the back side of the Moon, would an observer on the back side of the Moon ever see Earth?

In what alignment of the Sun, the Moon, and Earth does a solar eclipse occur?

In what alignment of the Sun, the Moon, and Earth does a lunar eclipse occur?

What does the Moon have in common with a compass needle?

If you were on the Moon and you looked up and saw a full Earth, would it be nighttime or daytime on the Moon?

If you were on the Moon and you looked up and saw a new Earth, would it be nighttime or daytime on the Moon?

Earth takes 365.25 days to revolve around the Sun. If Earth took this same amount of time to spin on its axis, what might we note about the Suns position in the sky?

Do astronomers make stellar observations during the full Moon part of the month or during the new Moon part of the month? Does it make a difference?

Nearly everybody has witnessed a lunar eclipse, but relatively few people have seen a solar eclipse. Why?

Because of Earths shadow, the partially eclipsed Moon looks like a cookie with a bite taken out of it. Explain with a sketch how the curvature of the bite indicates the size of Earth relative to the size of Moon. How does the tapering of the Suns rays affect the curvature of the bite?

Which of the three orientations of the Moon at sunset is most correct?

Assuming the illustrations depict a sunset, within 24 hours of when this scene is depicted will the Moon appear to be farther from or closer to the Sun?

Is the sailboat sailing at a location closer to the North Pole or closer to the equator? How can you tell?

Where and how would the Moon be positioned if the scenes were close to the North Pole?

In what sense is Pluto a potential comet?

Smaller chunks of asteroids are sent hurling toward Earth much more frequently than larger chunks of asteroids. Why?

Why are meteorites so much more easily found in Antarctica than in other continents?

A meteor is visible only once, but a comet may be visible at regular intervals throughout its lifetime. Why?

What would be the consequence of a comets tail sweeping across Earth?

Chances are about 5050 that in any night sky there is at least one visible comet that has not been discovered. This keeps amateur astronomers busy looking night after night, for the discoverer of a comet gets the honor of having it named for him or her. With this high probability of comets in the sky, why arent more of them found?

Project what human civilization would be like if Earth had no Moon.

What are the chances that microbial life forms might one day be found elsewhere in our solar system? How much effort should we spend on searching for such life forms, and what precautions should we take upon such a discovery?