Life In the Universe Two

Second Chapter

Why did ancient Greek anatomist believe that other worlds with life must exist?

They believed the universe was made from an infinite number of atoms.

Halving the distance between M1 and M2 would cause the gravitational force to?

increase by four

Increasing the distance between M1 and M2 by 10 would cause the gravitational force between them to?

Decrease by a factor of 100

Doubling the distance between M1 and M2 would cause the gravitional force between them to?

Decrease by a factor of four.

Who was Ptomley?

He developed a detailed, Earth centered model that remained in use for more than a thousand years.

Nicolaus Copernicus contributed by?

Creating a model with the sun rather then earth as the center.

Galileo observed..?

Phases of Venus

Mountains and valleys on the moon

four moons orbiting Jupiter

What are scientific models used for?

To make specific predictions that can be tested through observations or experiments

What is stellar parallax?

The slight back-and-forth shifting of a stars position relative to more distance stars that occurs over the course of a year.

In what way do planets move through our sky differently than the stars?

Over a few weeks, we see planets more relative to the stars, but we do not see The stars more relative to one another.

Lack of observable stellar parallax was interpreted to mean that?

Earth is at the center of the universe.

Suppose you want to observe the apparent retrograde motion of Mars, how long will it take?

Many months.

Retrograde motion is?

Instead of going west to east, planets appear to stop and go backwards from east to west.

How did Ptolemaic model explain the apparent retrograde motion of the planets. .

The planets moved along small circles that moved on larger circles around earth.

How did Kepler discover the laws of planetary motion?

Planetary orbits are elliptical rather than circular.

Copernicus model did not make to better predictions of planetary positions than the Ptolemaic model. Why?

He used perfect circles for the orbits of the planets.

Kepler third law, p² = a² tells us what?

More distant planets orbit the sun more slowly.

Mars move faster in its orbit when it is closer to the sun than when it is further from the sun. Which of Kepler's law explains this?

The second ( planets move faster when it closer and slower when it is further from the sun)

How does Venus appear in the sky to our naked eye

1. Sometimes shines brightly in the western sky shortly after sunset.

2. Venus sometimes shines brightly in the Easter sky shortly before dawn.

Suppose that Venus orbited earth as described in Ptolemy’s earth -centered model. When would Venus appear directly behind the sun as seen from earth?

Never

Science progresses through the creation and testing of models that explain observations as simply as possible. - What is this?

Hallmark of science

Suppose there were s Star with a parallax angle of one arc-second. How far away would it be?

3.26 light-years

Based on their inability to detect stellar parallax, the ancient Greeks concluded that _________.

either Earth is the center of the universe or stars are extremely far away

If the ancient Greeks had measured stellar parallax, they would have known that their belief in an Earth-centered universe was wrong. Why didn't the ancient Greeks measure stellar parallax?

Even for the nearest stars, parallax angles are too small to measure with the naked eye.

Why does stellar parallax occur?

We view nearby stars from different positions in Earth’s orbit at different times of the year.

Observations of stellar parallax provide direct evidence of what?

1. Some stars are more distant then others.

2. Earth orbits the sun.

Why did people have a hard time accepting Copernican model?

It is difficult because it is moving through space.

Even though the heliocentric model of Copernicus had advantages over Ptolemaic model, it suffered from the assumption of what?

Planets moved in perfect circles about the sun.

You discover an asteroid that orbits the Sun with the same 1-year orbital period as Earth.

The asteroid's average (semimajor axis) distance from the Sun is 1AU.