It makes conversions between units easy.
All astronomical distances are expressed in metric units.
It makes it easy to write big or small numbers.
All of the above
1 million km
1 million miles
1 light year
1 billion km
1 AU from Earth
More than 100 times the diameter of Earth
All of the above
Lots of gas and dust but very few stars.
Gas, dust, and stars, and a lot of dark matter.
A single star and planets.
Thousands of superclusters.
A force is needed to keep the moon in motion.
The moon moved at a constant velocity
A force is needed to pull the moon outward
A force is needed to pull the moon away from straight-line motion
All of the above
The deferent and the epicycle have to be attached to the sun and not the Earth.
The speed of a planet in its orbit depends on the size of the epicycle.
The mass of the planet determines how far the planet is from the sun.
A planet should move at its greatest speed when it is closest to the sun.
The most massive planets will have the greatest speed in their orbits.
A planet moves at a constant speed at all points in its orbit.
Uniform circular motion is adequate to describe the motion of all planets.
The distance between the planet and the sun changes as the planet orbits the sun.
The distance that a planet is from the sun depends on the mass of the planet.
Planets closer to the sun than Earth will show retrograde motion
Will decrease as the square of the distance between the two masses increases.
Will increase as the distance between the two masses increases.
Will cause the two masses to orbit each other
Will cause the two masses to move in a straight line.
Will cause the two masses to move away from each other.
The planets traveled in elliptical orbits about the Earth.
The center of the universe was the Sun with the Milky Way representing other distant planets.
The Earth was at the center of the universe.
The Sun was at the center of the universe.
Not visible in the night sky.
At the midpoint in the sky between east and west at sunrise.
At the midpoint in the sky between east and west at sunset.
At the midpoint in the sky between east and west at midnight.
At the midpoint in the sky between east and west at noon.
Travel in circular orbits with uniform motion
Were allowed to travel backwards in their orbits.
The planets orbited the Sun.
Traveled in elliptical orbits.
Traveled on epicycles whose centers followed orbits around the Sun
The smaller the orbit, the longer its orbital period
The larger the orbit, the longer its orbital period.
The smaller the diameter of a planet, the faster its rotational period
The orbital period of a planet is directly proportional to the diameter of the planet
Depends only on the speed of light
Depends only on the mass of the photon
Depends on both the mass and speed of the photon
Is proportional to the wavelength of the light.
Is inversely proportional to the wavelength of the light.
Will have a greater energy than short wavelength visible light
Will have a speed that is faster than short wavelength light.
Will appear blue in color to the average human eye
Will appear red in color to the average human eye
Has a higher frequency than short wavelength visible light
Have a greater energy than photons of red light
Have a greater energy than photons of ultraviolet light
Have a longer wavelength than photons of red light
Have a lower frequency than photons of red light
Travel at a greater speed than photons of red light
A unit of frequency
A unit of energy
A unit of mass
A unit of resolving power
A unit of length
Wavelength decreases from blue light to red light
Wavelength increases from blue light to red light
All colors of light have the same wavelength
Wavelength depends on intensity not color
One proton and one neutron
One proton and one electron
One proton, one neutron, and one electron
An isotope and an ion
There are about 10^11 stars in the Milky Way Galaxy, but there are ten times more stars that are made of dark matter
There are about 10^11 stars in the Milky Way Galaxy, but the mass of the Milky Way is about 10^12 times that of the Sun
There are about 10^13 stars in the Milky Way Galaxy, but the mass of the Milky Way is about 10^14 times that of the Sun
There are about 10^10 stars in the Milky Way Galaxy, but the mass of the Milky Way is about 10^12 times that of the Sun
125 million years
125 billion years
450 million years
225 million years
We find fossils in sedimentary layers, and no sediments were deposited until just a few hundred million years ago.
Life was far less abundant prior to a few hundred million years ago
Fossils could not form before there was oxygen in the atmosphere
Early organisms lacked skeletons and other hard structures that are most likely to be fossilized
From the current expansion rate we can work backward to estimate temperature and densities at various times in the early universe.
By looking all the way to the cosmological horizon, we can see the actual conditions that prevailed all the way back to the first instant of the Big Bang
The conditions in the very early universe must have been much like those found in stars today, so we learn about them by studying stars
We can only guess at the conditions, since we have no way to calculate or observe what they were.
"freezing out" was a term coined by particle physicists who think that the Big Bang theory is the ultimate theory for the Universe
These forces are important only at temperatures below the freezing point of water --- a temperature that the universe reached at an age of about 10^-35 seconds.
Prior to this time, the electroweak and strong forces were indistinguishable from each other, but after this time they behaved differently from each other
Following this time, neither the strong nor electroweak forces are ever important in the universe again
3: gravity, the strong force, and the electroweak force
1 force that represented the unification of all four forces that operate today
2: the strong force and the electroweak force
2: gravity and a single force that later became the strong, weak, and electromagnetic forces
Contains about 100 billion stars.
Is the largest known object in the universe.
Is about 200 light-years in diameter.
The mass of each object
The distance each object is from Earth.
The distance between two objects.
The speed of light.