Mastering Astronomy: Homework Two

Which of the following is not true about a scientific theory?

A theory is essentially an educated guess.

When Einstein's theory of gravity (general relativity) gained acceptance, it demonstrated that Newton's theory had been

incomplete.

Find the perihelion distance of Mars

1.382 a.u.

Find the aphelion distance of Mars.

1.666 a.u.

Match the following names and the major roles played in overturning the ancient belief in an Earth-centered universe.

Copernicus developed a model in which planets move around the Sun along perfectly circular orbits. Tycho provided a large amount of data from astronomical observations and suggested model in which the Sun orbits Earth while all other planets orbit the Sun. Kepler described the laws of planetary motion for the heliocentric model, according to which planets move around the Sun along elliptical orbits. Galileo answered the ancient objections to the heliocentric model, developed an enhanced telescope, and provided evidence in favor of the heliocentric model.

Earth is closer to the Sun in January than in July. Therefore, in accord with Kepler's second law:

Earth travels faster in its orbit around the Sun in January than in July.

The dwarf planet Eris orbits the Sun every 557 years. What its average distance (semimajor axis) from the Sun?

Eris's semimajor axis = 67.7 a.u.

Which of the following was not a major advantage of Copernicus's Sun-centered model over the Ptolemaic model?

It made significantly better predictions of planetary positions in our sky.

According to Kepler's third law,

Jupiter orbits the Sun at a faster speed than Saturn.

Which of the following is not true about scientific progress?

Science advances only through the scientific method.

Summarize the development of the Greek geocentric model through Ptolemy. How did the Ptolemaic model account for apparent retrograde motion?

The Ptolemiac model was able to explain retrograde motion by having the planets move on smaller circles attached to the larger circles on which they went around Earth.

In the Greek geocentric model, the retrograde motion of a planet occurs when:

The planet actually goes backward in its orbit around Earth.

When I looked into the dark lanes of the Milky Way with my binoculars, I saw what must have been a cluster of distant galaxies.

This statement does not make sense, because we cannot see through the band of light we call the Milky Way to external galaxies; the dark fissure is gas and dust blocking our view.

The dwarf planet Eris orbits the Sun every 557 years. How does its average distance compare to that of Pluto?

aEris/aPluto = 1.72

You are an astronomer on planet Tirth, which orbits a distant star. It has recently been accepted that Tirth is spherical in shape, though no one knows its size. One day, you learn that on the equinox your sun is directly overhead in the city of Tyene, located 400 kilometers due north of you. On the equinox, you go outside in Alectown and observe that the altitude of your sun is 87 ∘. What is the circumference of Tirth?

circumference of Tirth = 4.8×104 km

Galileo's contribution to astronomy included:

making observations and conducting experiments that dispelled scientific objections to the Sun-centered model.

When it is summer in Australia, the season in the United States is

winter

There are 360∘ in a full circle. What is the Moon's angular size in arcseconds?

θMoon = 1800 ′′

There are 360∘ in a full circle. The Moon's angular size is about 12∘. What is this in arcminutes?

θMoon = 30 ′

There are 360∘ in a full circle. How many arcseconds are in a full circle?

θ◯ = 1296000 ′′

There are 360∘ in a full circle. How many arcminutes are in a full circle?

θ◯ = 21600 ′