Astronomy Midterm #2 Units 3 and 4

The mathematical form of Kepler's third law measures the period in years and the ______________ in astronomical units (AU).

semimajor axis

A planet is discovered orbiting the star 51 Peg with a period of four days (0.01 years). 51 Peg has the same mass as the Sun. Mercury's orbital period is 0.24 years, and Venus's is 0.62 years. The average orbital radius of this planet is

less than Mercury's.

The Moon takes roughly 28 days to complete one orbit around Earth. If the orbital radius of the Moon were twice its actual value, its orbital period would be

more than 56 days.

According to Kepler's second law, Pluto will be traveling fastest around the Sun when at

perihelion

Why are astronauts (and other objects) weightless inside the International Space Station as it orbits Earth?

they are in free-fall

As a comet orbits around the Sun, its maximum speed is twice its minimum speed. What can we say about its orbit?

The comet is twice as far from the Sun at aphelion as at perihelion.

According to Kepler's second law, Jupiter will be traveling most slowly around the Sun when at

aphelion

Suppose you drive from home to your child's school, pick her up, and drive back home, covering a total distance of 25 miles in 1 hour. Which of the following statements are true?

Your average speed for the trip is 25 miles per hour. Your velocity is different on the return home than it is on the way to school. You must accelerate when you reach the school.

Why do the planets orbit the Sun (i.e. why don't they crash into the Sun)?

Although the planets experience a force of gravity from the Sun, since they are moving, their trajectories bend around the Sun rather than lead directly into the Sun.

Suppose two comets, comet A and comet B, were orbiting the Sun, having the same average orbital radii. If comet A had a higher eccentricity than comet B, which comet would, during some portion of its orbit, have the highest orbital speed?

Comet A.

Kepler's third law states that a planet's orbital period, p, is related to its average (semimajor axis) orbital distance, a, according to the mathematical relationship p2=a3p2=a3. Which of the following statements describe a characteristic of the solar system that is explained by Kepler's third law?

Inner planets orbit the Sun at higher speed than outer planets Venus orbits the Sun faster than Earth orbits the Sun.

If an astronomer claims to have discovered an object with a very eccentric orbit, which of the following best describes the orbital trajectory of the object?

It looks like a very squashed oval.

Two planets are observed going around a star. Planet Xoron has an orbital period that is twice as long as planet Krypton. Which planet has a shorter average orbital radius?

Planet Krypton

The extent to which Mars' orbit differs from a perfect circle is called its

eccentricity

Earth orbits in the shape of a/an ________ around the Sun.

elipse

Earth is located at one ________ of the Moon's orbit.

focus

If Earth's orbit were very eccentric, but the average distance from the Sun were still 1 AU, its orbital period

would still be one year.