PHY 109

semimajor axis

half of the distance across the ellipse in its longest direction, which is also the planet's average distance from the Sun

Consider a planet with an elliptical orbit around the Sun. Its average distance from the Sun is __________.

half the distance along a line from the nearest to the farthest points in its orbit

As a giant cloud of gas collapses due to gravity, you would expect its rate of rotation to

increase

As an object heats up, its thermal energy __________.

increases

As the cloud shrinks in size, its central temperature __________ as a result of its __________.

increases ; gravitational potential energy being converted to thermal energy

falsifiable

it could potentially be proven false

Why wasn't the Sun-centered model of Copernicus immediately adopted after he proposed it?

it was not noticeably more accurate than the old Ptolemaic model

We describe a location on Earth's surface by stating its _________.

latitude and longitude

As the cloud shrinks in size, its rate of rotation --------- because ________________________

speeds up; its total angular momentum is conserved

If the Sun were to shrink, its angular momentum would __________.

stay the same

As an object shrinks in size, its mass __________. (Assume the object is not ejecting any mass and that no mass is coming in from beyond the object.)

stays the same

The gravitational attraction between Earth and the Sun is __________ the gravitational attraction between Earth and the Moon.

stronger than

The shadow cast by a simple stick or obelisk allowed ancient people to

tell the time of day

How far away is the Andromeda Galaxy?

2.5 million light years

The Andromeda Galaxy is faintly visible to the naked eye. When you look at the Andromeda Galaxy, the retina of your eye is absorbing light that has traveled through space for ______ to reach you.

2.5 million years

Suppose that someone in the Andromeda galaxy had a super-telescope through which they were looking at Earth right now. They would see Earth ______.

2.5 million years ago

What is the earth's tilt?

23.5 degrees

The distance between the center of the Milky Way Galaxy and our solar system is approximately __________.

28,000 light years

What is stellar parallax?

It is the slight back-and-forth shifting of star positions that occurs as we view the stars from different positions in Earth's orbit of the Sun.

Essentially all chemical elements heavier than hydrogen and helium, including carbon and oxygen, were made __________.

by nuclear fusion in massive stars

meridian

A half-circle extending from your horizon due north, through your zenith, to your horizon due south

Earth has two tidal bulges at all times. Approximately where are these bulges located?

One faces the Moon and one faces opposite the Moon.

During the time that a planet is in its period of apparent retrograde motion: _________

Over many days or weeks, the planet moves westward relative to the stars, rather than the usual eastward relative to the stars

circumpolar

Part complete Stars that are visible in the local sky on any clear night of the year, at any time of the night

What is the saros cycle?

The roughly 18-year cycle over which the pattern of eclipses repeats

As a gas cloud collapses, shrinking in size, its total gravitational potential energy __________.

decreases

According to Newton's second law, the greater the force exerted on an object, the greater the object's _____.

acceleration

As the universe expands, its overall temperature _________.

decreases

Radiative energy is __________.

energy carried by light

Where along its orbit would the Moon also have its daylight side on the right and its night side on the left?

everywhere along its orbit

Part complete Lunar eclipses can occur only during a _________

full moon

The video shows a collapsing cloud of interstellar gas, which is held together by the mutual gravitational attraction of all the atoms and molecules that make up the cloud. As the cloud collapses, the overall force of gravity that draws the cloud inward _______________ because the strength of gravity follows _______________ with distance.

gradually becomes stronger; an inverse square law

The gravitational potential energy of a contracting interstellar cloud

gradually transforms into other forms of energy.

The orbital energy of an asteroid orbiting the Sun is the sum of its _________.

gravitational potential energy and kinetic energy

The star Betelgeuse is about 600 light-years away. If it explodes tonight...

we won't know about it until 600 years from now.

The point directly over your head is called _________.

zenith

a perfect circle has an eccentricity of...

zero

The Moon's orbital period around Earth is roughly __________.

1 month

three things that are consistent with the hallmarks of science

1. A scientific model must make testable predictions. 2. Science progresses through the creation and testing of models that explain observation as simply as possible. 3. Scientific explanations should be based solely on natural causes.

three statements about ellipses

1. An ellipse with a large eccentricity looks much more elongated (stretched out) than an ellipse with a small eccentricity. 2. The semimajor axis of an ellipse is half the length of the longest line that you can draw across an ellipse. 3. A circle is considered to be a special type of ellipse.

Three facts about the motion of the Earth

1. Earth and our solar system moves with the Milky Way galaxy relative to other galaxies in our Local Group. 2. Earth orbits the Sun. 3. Earth moves with the Sun on an orbit around the center of the Milky Way galaxy.

Two things about tides

1. High tides are highest at both full moon and new moon. 2. Low tides are lowest at both full moon and new moon.

three hallmarks of science

1. Science progresses through the creation and testing of models of nature that explain the observations as simply as possible. 2. Modern science seeks explanations for observed phenomena that rely solely on natural causes. 3. Models must make testable predictions that will force us to revise or abandon the model if they do not agree with observations.

two things true in the Northern Hemisphere

1. Sun reaches highest point in local sky on June solstice 2. At high latitudes, Sun never rises on December solstice

Three things that are true about the universe:

1. The average distance increases with time between galaxies in the universe. 2. observer in any galaxy sees more distant galaxies moving away faster 3. galaxies stay roughly the same size as the universe expands

Galileo refuted these three ideas...

1. Venus orbits Earth. 2. heavenly bodies are perfect. 3. objects require an external force to keep moving.

three things true in the Southern Hemisphere:

1.Sun is above horizon for the longest time on 2.December solsticeSun traces shortest path across local sky on June solstice 3. At high latitudes, Sun never sets on December solstice

four statements about the phases of the moons:

1.if it is full moon, the Moon will rise around sunset 2.the time between new moon and full moon is about two weeks 3.at new moon, we see only the "night" side of the Moon 4.at new moon, the half of the Moon facing the Sun is fully illuminated

Part complete If Earth were twice as far from the Sun, the force of gravity attracting Earth to the Sun would be

1/4 as strong

The disk of the Milky Way galaxy has a diameter of approximately

100,000 light years

What is the Earth's diameter?

12,800 km

what is the moon's diameter?

3500 km

How old is our solar system?

4.5 billion years ago

The sun rises and sets each day because

Earth rotates once each day

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.

What is really happening in space during the periods when we see Mars going through apparent retrograde motion?

Earth is passing by Mars in its orbit around the Sun.

According to the law of universal gravitation, what would happen to Earth if the Sun were somehow replaced by a black hole of the same mass?

Earth's orbit would not change.

The ecliptic plane is defined by...

Earth's orbital path around the Sun.

Each choice below describes how a few astronomical phenomena are related to time periods. Which list is entirely correct?

Earth's rotation defines a day. The cycle of the Moon's phases takes about a month. Earth's orbit defines a year. Earth's cycle of axis precession takes 26,000 years.

Where does the Sun remain above the horizon all day (never setting) on the December solstice?

Everywhere between the Antarctic Circle (latitude 66.5°S) and the South Pole

T/F: Everywhere on the earth Sun reaches zenith (altitude 90 degrees) every day at noon

False

Suppose you have already calculated the gravitational force, which we will call Fg , attracting Earth and the Moon. Then the amount of acceleration of Earth due to this force is __________.

Fg divided by the mass of the Earth

Rank largest to smallest: Sun, Solar System, Galaxy, Earth

Galaxy> Solar System > Sun > Earth

If you are located in the Northern Hemisphere, which of the following correctly describes a relationship between the sky and your location?

The altitude of the north celestial pole equals your latitude.

what do astronomers mean when they say that the universe is expanding?

The average distance between galaxies is increasing with time

what do we mean by the Milky Way in our sky?

The patchy band of light that outlines the plane of the Milky Way Galaxy as seen from Earth.

Ecliptic

The path the Sun appears to trace around the celestial sphere each year

Which of the following best describes why we have seasons on Earth?

The tilt of Earth's axis causes different portions of the Earth to receive more or less direct sunlight at different times of year.

Rank largest to smallest: Milk Way, local group, Jupiter, our solar system, local supercluster, universe, Sun, Earth

The universe>the local supercluster>the local group>the Milky Way galaxy>our solar system>the Sun>Jupiter>Earth

Why did the Greeks conclude that the Earth was stationary, and that the Sun and the planets orbited around the Earth?

They did not observe any change in the separation of stars during Earth's orbit

What is true about Tycho, Kepler, and Newton?

Tycho collected the data, Kepler provided the model in the form of laws, Newton explained the model in terms of gravity.

If stars existed but galaxies did not:

We would not exist because we are made of material that required recycling in galaxies.

Do tides affect Earth's atmosphere?

Yes, because atmospheric gas has mass.

Do tides also affect land?

Yes, though land rises and falls by a much smaller amount than the oceans.

About how many stars are visible to the naked eye on a clear, dark night away from city lights?

a couple thousand

eccentricity

a measure of how "stretched out" an ellipse is.

We cannot see a new moon in our sky because _________.

a new moon is quite near the Sun in the sky

Kepler's third law states that for any planet orbiting the Sun, the orbital period squared (p2 ) is equal to the average orbital distance cubed (a3), or p2=a3 . This implies that __________.

a planet with a large average distance from the Sun has a longer orbital period than a planet with a smaller average distance from the Sun

constellation

a region in the sky as seen from Earth.

The Orion Nebula is __________.

a star-forming cloud located far outside our solar system

Galaxy

a very large collection of stars held together by gravity

When is the birth of the universe? When did the Big Bang occur?

about 14 billion years ago

If we have a new moon today, when we will have the next full moon?

about two weeks

Kepler's first law tells us that the orbit of a planet must be...

an ellipse with the Sun at one focus

How far away is Alpha Centauri from the Earth?

approximately four light-years

According to Kepler's second law, as a planet or other object moves around its orbit, it sweeps out equal __________ in equal __________.

areas; times

Why does the Moon play a greater role in causing tides than the Sun?

because the gravitational attraction between Earth and the Moon varies more across Earth than does the gravitational attraction between Earth and the Sun

We say that the force of gravity follows an inverse square law with distance. This means that the force attracting two objects _________ as two objects come closer together.

becomes stronger

Consider a time when Mars is in the middle of one of its periods of apparent retrograde motion. During this time, Mars appears ________ in our night sky and crosses the meridian around ________.

brightest; midnight

Kepler's third law tells us that for a planet orbiting the Sun, the planet mass...

does not affect the orbital period

the moon is always illuminated by the sun except for ....

during a lunar eclipse

At most times, Mars appears to move _________ relative to the stars. The exceptions are during its periods of apparent retrograde motion, when Mars appears to move _________ relative to the stars.

eastward, westward

As seen from Earth, the Sun appears to follow the annual path that we call the __________ around the celestial sphere.

ecliptic

Compared to their values on Earth, on another planet your

mass would be the same but your weight would be different.

Two stars that are in the same constellation:

may actually be very far from each other

To calculate the gravitational force between two objects we __________, and then multiply by the gravitational constant G.

multiply the two masses, divide by their distance squared

Perihelion

nearest point to the sun in the orbit of a heavenly body

According to Kepler's second law, planets or other objects orbiting the Sun move fastest when they are __________.

nearest to the sun

a total solar eclipse can only happen during what lunar phase?

new

Galileo challenged the idea that objects in the heavens were perfect by ________.

observing sunspots on the Sun and mountains on the Moon

According to the Greek Earth-centered model of the universe, apparent retrograde motion __________.

occurred because planets moved in small circles that in turn moved in larger circles around Earth

sidereal

of or related to stars

the seasons in Australia is ______ of the United States

opposite

The time a planet takes to complete one orbit is called its __________.

orbital period

If you wanted to document the apparent retrograde motion of Mars, you would need to measure and record Mars's ________ ________ _________ _________ over a period of __________ __________.

position among the constellations ; several months

A rock starting from rest on a high cliff, then moving faster and faster as it falls represents a change from ...

potential energy to kinetic energy

Explanations

provide possible reasons for what we measure or observe, not necessarily correct

celestial sphere

representation of how the entire sky looks as seen from Earth.

Consider Earth and the Moon. As you should now realize, the gravitational force that Earth exerts on the Moon is equal and opposite to that which the Moon exerts on Earth. Therefore, according to Newton's second law of motion __________.

the Moon has a larger acceleration than Earth, because it has a smaller mass

The fact that we always see the same face of the Moon tells us that

the Moon's rotation period is the same as its orbital period.

Astronomical Unit (AU)

the average distance between Earth and the sun, about 150 million km

Lightyear (ly)

the distance light travels in one year

The word "apparent" in apparent retrograde motion is meant to imply that __________.

the motion appears backward as we see it from Earth, but it is not really backward in space

What is Alpha Centauri?

the nearest star (or star system) besides our Sun, about 4 light-years away

An original observation of Galileo's that helped to overturn the ancient Earth-centered model was

the phases of Venus

Aphelion

the point in a planet's orbit that is farthest from the Sun.

if the distances between pairs of objects are all the same, then the strength of gravity depends only on __________.

the product of the two object masses (M1×M2)

In January, Earth's rotation axis points in the direction of...

the star Polaris

In July, Earth's rotation axis points in the direction of...

the star Polaris

The force of gravity follows an inverse square law, meaning that ...

the strength of the force declines with the square of the distance between two masses

According to Newton's third law...

the strength of the force that the object on the left exerts on the object on the right has to be exactly the same (but in an opposite direction) as the force the object on the right exerts on the object on the left

universe

the sum total of all matter, energy, space, and time

Rank these from oldest to youngest: dinosaurs go extinct nuclear fusion begins in the sun the universe begins to expand earliest humans earliest life on year elements such as carbon and oxygen first exist

the universe begins to expand elements such as carbon and oxygen first exist nuclear fusion begins in the sun earliest life on year dinosaurs go extinct earliest humans

The key discovery that led to the idea of the Big Bang was that __________.

the universe is expanding

which two properties of distant galaxies do astronomers have to measure to show that we live in an expanding universe?

their distances and speeds

Observations

things that we can directly see or measure.

A week after full moon, the Moon's phase is:

third quarter

When we say that a quantity is conserved, we mean that its value does not change. Which of the following are examples of quantities that are conserved for a system of objects?

total energy, total angular momentum, total momentum

On Dec. 21, the Sun is directly above the ____________.

tropic of Capricorn

Any particular location on Earth experiences __________.

two high tides and two low tides each day