# Astronomy Homework2

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### What practical value did astronomy offer to ancient civilizations?

It helped them keep track of time and seasons, and it was used by some cultures for navigation.

### Scientific thinking is _________.

based on everyday ideas of observation and trial-and-error experiments

### What is Kepler's first law?

Kepler's first law states that the orbit of each planet is an ellipse with the Sun at one focus

### What is Kepler's second law?

Kepler's second law states that as a planet orbits the Sun, it sweeps out equal areas in equal times

### What is Kepler's third law?

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=a3.

### We never see a crescent Jupiter from Earth because Jupiter __________.

An object must come between Earth and the Sun for us to see it in a crescent phase, which is why we see crescents only for Mercury, Venus, and the Moon.

### In Ptolemy's Earth-centered model for the solar system (not shown), Venus's phase is never full as viewed from Earth because it always lies between Earth and the Sun. In reality, as Galileo first recognized, Venus is __________.

full whenever it is on the opposite side of the Sun from Earth, although we cannot see the full Venus because it is close to the Sun in the sky

at noon

at noon

### When would you expect to see Venus high in the sky at midnight?

never; For Venus to be high in the sky at midnight, it would have to be on the opposite side of our sky from the Sun. But that never occurs, because Venus is closer than Earth to the Sun.

### In Ptolemy's Earth-centered model for the solar system (not shown), Venus always stays close to the Sun in the sky and, because it always stays between Earth and the Sun, its phases range only between new and crescent. The following statements are all true and were all observed by Galileo. Which one provides evidence that Venus orbits the Sun and not Earth?

We sometimes see gibbous (nearly but not quite full) Venus.

### How did the Ptolemaic model explain the apparent retrograde motion of the planets?

The planets moved along small circles that moved on larger circles around the Earth.

### When Copernicus first created his Sun-centered model of the universe, it did not lead to substantially better predictions of planetary positions than the Ptolemaic model. Why not?

Copernicus used perfect circles for the orbits of the planets.

### According to Kepler's third law (p2 = a3), how does a planet's mass affect its orbit around the Sun?

A planet's mass has no effect on its orbit around the Sun.

### The Muslim fast of Ramadan occurs

during the ninth month of a 12-month lunar cycle.

### The Metonic cycle is the

19-year period over which the lunar phases occur on about the same dates.

### The Jewish calendar is kept roughly synchronized with a solar calendar by

adding a thirteenth lunar month to 7 out of every 19 years.

False

true

true

true

true

### Which of the following statements expresses what we mean by a scientific theory?

A simple model that explains a wide variety of phenomena and that has survived repeated tests

### Which of the following is the reason for the solar day being longer than a sidereal day?

the combined effect of the rotation of Earth and its orbit about the Sun

### When did humans first learn that Earth is not the center of the universe?

within the past 500 years

### The principle of Occam's Razor states that

in explaining natural phenomena, the simplest explanation consistent with the observations is to be preferred.

### From Kepler's third law, an asteroid with an orbital period of 8 years lies at an average distance from the Sun equal to

4 astronomical units.

### Kepler's second law, which states that as a planet moves around its orbit it sweeps out equal areas in equal times, means that

a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun.

### One of the "nails in the coffin" for the Earth-centered universe was

Galileo's observations of the moons of Jupiter.

### How did Eratosthenes estimate the size of Earth in 240 B.C.?

by comparing the maximum altitude of the Sun in two cities at different latitudes

### What do we mean by a geocentric model of the universe?

A model designed to explain what we see in the sky while having the Earth located in the center of the universe.

### If the Sun rises precisely due east:

it must be the day of either the spring or fall equinox.

### Refer to the data in the introduction. Rank the seasons for the Northern Hemisphere based on Earth's distance from the Sun when each season begins, from closest to farthest.

winter, spring, fall, summer

### Refer to the data in the introduction. Rank the seasons for the Southern Hemisphere based on Earth's distance from the Sun when each season begins, from closest to farthest.

summer, fall, spring, winter

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