Question 1

An inferior planet moves more or less directly toward Earth at greatest eastern elongation. What does this mean for an observer is watching the night-by-night motion of this planet against the background stars?

Accepted Answer

At greatest eastern elongation, an inferior planet (one that orbits closer to the Sun than Earth, such as Mercury or Venus) appears to pause in its motion against the background stars from Earth's perspective. This is because it is transitioning from moving eastward relative to the stars (direct motion) to moving westward (retrograde motion), creating a moment where its motion relative to the stars appears to halt.

Question 2

How did Copernicus know Jupiter's orbit around the Sun was larger than that of Earth?

Accepted Answer

Copernicus knew Jupiter's orbit around the Sun was larger than that of Earth because it can be high in the sky at midnight, indicating it is on the opposite side of Earth from the Sun, which would only be possible if its orbit is larger than Earth's.

Question 3

Greatest elongation in a planetary orbit occurs when the angle from the

Accepted Answer

The answer of Greatest elongation in a planetary orbit occurs...

Question 4

When a planet is seen at opposition, it is always at its

Accepted Answer

When a planet is seen at opposition, it means it is directly opposite the Sun from Earth's perspective, making it at its closest point to Earth.

Question 5

Where and when would Jupiter be seen from Earth when it is at opposition?

Accepted Answer

When Jupiter is at opposition, it is directly opposite the Sun from Earth's perspective, meaning it rises as the Sun sets and is visible all night, reaching its highest point in the sky at local midnight.

Question 6

Which of these planetary configurations is impossible for an inferior planet?

Accepted Answer

An inferior planet, such as Mercury or Venus, cannot be at opposition because opposition occurs when a planet is on the opposite side of the Earth from the Sun, which is only possible for superior planets.

Question 7

The eastern elongation of Mercury's orbit

Accepted Answer

The eastern elongation of Mercury's orbit depends on both Mercury's and Earth's positions in their respective orbits, as these positions determine the angle at which Mercury is observed from Earth.

Question 8

At what position in its orbit does an inferior planet appear to be moving (for a day or two) more or less directly toward Earth? See Figure 2-4.

Accepted Answer

The answer of At what position in its orbit does...

Question 9

Which of these planetary configurations is NOT possible for the planet Mercury?

Accepted Answer

Mercury, being an inferior planet (one that orbits closer to the Sun than Earth does), cannot be in opposition to Earth. Opposition occurs when a planet is on the opposite side of the Earth from the Sun, which is only possible for superior planets (those that orbit farther from the Sun than Earth does).

Question 10

When Venus is at superior conjunction, it is

Accepted Answer

At superior conjunction, Venus is on the opposite side of the Sun from Earth, which places it at its greatest distance from Earth.

Question 11

When Mars is at opposition, it is

Accepted Answer

When Mars is at opposition, it is directly opposite the Sun in the sky, meaning it is highest in the sky at midnight.

Question 12

In what direction is Venus moving when it is at greatest elongation?

Accepted Answer

The answer of In what direction is Venus moving when...

Question 13

Which of these describes a configuration in which Venus could be seen from Earth when it is at greatest elongation?

Accepted Answer

Venus, when at its greatest elongation, is farthest from the Sun from Earth's perspective, making it visible in the sky either just after sunset or just before sunrise, depending on its position in its orbit. When it is visible just after sunset, it appears in the western sky, because it is then setting after the Sun from the observer's viewpoint on Earth.

Question 14

When Saturn is at its farthest distance from Earth, it is at

Accepted Answer

Conjunction occurs when Saturn is on the opposite side of the Sun from Earth, making it the farthest from Earth.

Question 15

In which part of the sky could Venus appear at sunset when it is at greatest elongation?

Accepted Answer

Venus can appear in the western part of the sky at sunset when it is at its greatest elongation as an "evening star." This is because it is positioned in its orbit in such a way that it is visible above the horizon after the Sun has set.

Question 16

The time from one inferior conjunction of Mercury to the next inferior conjunction of Mercury is 116 days. The time from one superior conjunction of Mercury to the next superior conjunction is

Accepted Answer

The time from one superior conjunction of Mercury to the next is also 116 days, just like the time from one inferior conjunction to the next. This is because both types of conjunctions are part of Mercury's synodic period, which is the time it takes for Mercury to return to the same position in the sky as seen from Earth.

Question 17

The planet Venus can never reach which planetary configuration when viewed from Earth?

Accepted Answer

Venus, being an inferior planet (one that orbits the sun closer than Earth), can never be in opposition, which is a configuration where the Earth is directly between the sun and the planet. This configuration is only possible for superior planets (those that orbit the sun further out than Earth).

Question 18

The BEST time(s) to see inferior planets from Earth is (are) when these planets are at positions of

Accepted Answer

Greatest elongation is the best time to view inferior planets (Mercury and Venus) from Earth because it is when these planets are farthest from the Sun in the sky, making them visible either in the evening or morning sky without being outshone by the Sun.

Question 19

What is the angle between the line from Earth to Mercury and the line from Mercury to the Sun when Mercury is at greatest elongation?

Accepted Answer

At greatest elongation, the angle between the line from Earth to Mercury and the line from Mercury to the Sun is 90°. This is because greatest elongation occurs when Mercury appears farthest from the Sun in the sky, which geometrically corresponds to a right angle from our viewpoint on Earth.

Question 20

How did Copernicus know Mercury was closer to the Sun than Earth?

Accepted Answer

Mercury is always observed close to the Sun in the sky, indicating it orbits closer to the Sun than Earth does.

Quiz 2: Gravitation and the Motion of the Planets