AST 101: Lesson 3

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 draws the cloud inward __________ because __________.

(Blank 1) gradually becomes stronger (Blank 2) the strength of gravity follows an inverse square law with distance

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

(Blank 1) increases (Blank 2) gravitational potential energy being converted to thermal energy

As the cloud shrinks in size, its rate of rotation __________ because __________.

(Blank 1) speeds up (Blank 2) its total angular momentum is conserved

As you watch the video, notice that the size of the tidal bulges varies with the Moon's phase, which depends on its orbital position relative to the Sun. Which of the following statement(s) accurately describe(s) this variation?

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

Radio waves are:

a form of light

Electromagnetic radiation is always dangerous. (T/F)

false

Notice that the Sun's spectrum appears brightest (or most intense) in the yellow-green region. This fact tells us __________.

the approximate temperature of the Sun's surface (One of the two laws of thermal radiation (Wien's law) states that the peak wavelength of a spectrum is directly related to an object's temperature. A peak at yellow-green wavelengths corresponds to a temperature of about 5800 K.)

Compared to its angular momentum when it is farthest from the Sun, Earth's angular momentum when it is nearest to the Sun is

the same.

Any particular location on Earth experiences __________.

two high tides and two low tides each day

Which of the following forms of light can be observed with telescopes at sea level?

visible light and radio waves

As shown in the video, Earth has two tidal bulges at all times. Approximately where are these bulges located?

One faces the Moon and one faces opposite the Moon.

If the Moon were closer to Earth, high tides would

be higher than they are now

You have found that tides on Earth are determined primarily by the position of the Moon, with the Sun playing only a secondary role. 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 Submit

The set of spectral lines that we see in a star's spectrum depends on the star's:

chemical composition

A star whose spectrum peaks in the infrared is:

cooler than our Sun.

Compared to red light, blue light has higher frequency and

higher energy and shorter wavelength.

The James Webb Space Telescope is designed primarily to observe __________.

infrared light

Compared to an atom as a whole, an atomic nucleus:

is very tiny but has most of the mass.

Which of the six numbered features represents absorption lines?

5 - above infared

A planet with the same mass as Earth orbiting at a distance of 1 AU from a star with four times the Sun's mass.

6 months

Each of the following diagrams shows a spaceship somewhere along the way between Earth and the Moon (not to scale); the midpoint of the distance is marked to make it easier to see how the locations compare. Assume the spaceship has the same mass throughout the trip (that is, it is not burning any fuel). Rank the five positions of the spaceship from left to right based on the strength of the gravitational force that Earth exerts on the spaceship, from strongest to weakest.

Gravity follows an inverse square law with distance, which means the force of gravity between Earth and the spaceship weakens as the spaceship gets farther from Earth.

The following diagrams are the same as those from Part A. This time, rank the pairs from left to right based on the size of the acceleration the asteroid on the left would have due to the gravitational force exerted on it by the object on the right, from largest to smallest. - asteroid:sun - asteroid:earth - asteroid:moon - asteroid:asteroid - asteroid:hydrogen atom

According to Newton's second law, the asteroid with the largest acceleration will be the one that has the strongest gravitational force exerted on it by the object on the right. That is why the ranking here is the same as the ranking for Part A.

The following five diagrams show pairs of astronomical objects that are all separated by the same distance d. Assume the asteroids are all identical and relatively small, just a few kilometers across. Considering only the two objects shown in each pair, rank the strength, from strongest to weakest, of the gravitational force acting on the asteroid on the left. - asteroid:sun - asteroid:earth - asteroid:moon - asteroid:asteroid - asteroid:hydrogen atom

Because the distance is the same for all five cases, the gravitational force depends only on the product of the masses. And because the same asteroid is on the left in all five cases, the relative strength of gravitational force depends on the mass of the object on the right

Suppose we want to know what the Sun is made of. What should we do?

Compare the wavelengths of lines in the Sun's spectrum to the wavelengths of lines produced by chemical elements in the laboratory. (Each chemical element (or ion or molecule) produces a unique set of spectral lines; the wavelengths of these lines can be measured in the laboratory. If the Sun's spectrum contains the set of lines for some particular element, we conclude that the Sun contains that element. We determine the Sun's overall chemical composition by examining all the lines in its spectrum.)

Why is a sunflower yellow?

It reflects yellow light.

Most people are familiar with the rise and fall of ocean tides. Do tides also affect land?

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

Which of the six numbered features represents emission lines?

1 - above ultraviolet

A planet with twice Earth's mass orbiting at a distance of 1 AU from a star with the same mass as the Sun.

1 year

Which person is weightless?

A child in the air as she plays on a trampoline.

Suppose that the Sun were to collapse from its current radius of about 700,000 km to a radius of only about 6000 km (about the radius of Earth). What would you expect to happen as a result?

A tremendous amount of gravitational potential energy would be converted into other forms of energy, and the Sun would spin much more rapidly.

Each diagram below shows a pair of spectra with a set of spectral lines. The top spectrum always shows the lines as they appear in a spectrum created in a laboratory on Earth ("Lab") and the bottom spectrum shows the same set of lines from a distant star. The left (blue/violet) end of each spectrum corresponds to shorter wavelengths and the right (red) end to longer wavelengths. Rank the five stars based on the Doppler shifts of their spectra, from largest blueshift, through no shift, to largest redshift.

As your answer correctly indicates, lines that are shifted to the left (toward the blue/violet) compared to the laboratory spectrum represent blue shifts, and lines shifted to the right (toward the red) represent redshifts.

The diagrams below each show the motion of a distant star relative to Earth (not to scale). The red arrows indicate the speed and direction of the star's motion: Longer arrows mean faster speed. Rank the stars based on the Doppler shift that we would detect on Earth, from largest blueshift, through no shift, to largest redshift.

As your correct answer indicates, the star moving fastest toward Earth will have the greatest blueshift, the star moving across our line of sight will have no shift at all, and the star moving fastest away from us will have the greatest redshift.

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 following diagrams are the same as those from Part A. This time, rank the five positions of the spaceship from left to right based on the strength of the gravitational force that the Moon exerts on the spaceship, from strongest to weakest.

Gravity follows an inverse square law with distance, which means the force of gravity between the Moon and the spaceship increases as the spaceship approaches the Moon. Now continue to Part C for activities that look at the effects of both distance and mass on gravity.

Suppose that two asteroids are orbiting the Sun on nearly identical orbits, and they happen to pass close enough to each other to have their orbits altered by this gravitational encounter. If one of the asteroids ends up moving to an orbit that is closer to the Sun, what happens to the other asteroid?

It will end up on an orbit that is farther from the Sun. (Total energy must be conserved, so if one asteroid loses energy and moves to a closer orbit, the other must gain energy and move to a more distant orbit.)

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

Newton's second law of motion, F=ma, means that for a particular force F, the product mass x acceleration must always be the same. Therefore if mass is larger, acceleration must be smaller, and vice versa.

The following diagrams are the same as those from Part A. Again considering only the two objects shown in each pair, this time rank the strength, from strongest to weakest, of the gravitational force acting on the object on the right. - asteroid:sun - asteroid:earth - asteroid:moon - asteroid:asteroid - asteroid:hydrogen atom

Newton's third law tells us that the gravitational force exerted on the asteroid on the left by the object on the right will be equal in magnitude, but opposite in direction to the gravitational force exerted on the object on the right by the asteroid on the left. That is why the ranking here is the same as the ranking for Part A.

Part ALet's start with an example from history. Listed below are a series of claims regarding United States President John F. Kennedy (1917-1963). Classify each statement according to whether or not it is falsifiable. [Falsifiable:could be proven false] - Kennedy was the 35th president of the United States - Kennedy died from a bullet in his brain [Not falsifiable:could not be proven false] - Kennedy's death was the will of God - The murder of John F. Kennedy was an act of evil - If he'd lived, Kennedy would have ended the Vietnam War - Kennedy's murder was orchestrated by an undetectable shadow government of the United States

Note that both of the falsifiable claims in this example happen to be true. The claim about Kennedy being the 35th President is falsifiable because it can be checked against historical records. The claim that Kennedy died from a bullet in his brain is falsifiable because it could have been shown false by the medical examiner. The remaining claims are not falsifiable: Statements that call on any type of supernatural being are by definition out of the realm of science. Similarly, a claim of something being "undetectable" could not be falsified, and a claim about what Kennedy would have done if he had lived is a conjecture that cannot be disproven.

Classify each claim according to whether or not it is falsifiable.[Falsifiable:could be proven false] - The chemical content of the universe is mostly hydrogen and helium - Earth is at the center of the solar system - The Sun is at the center of the solar system - The observable universe contains approximately 100 billion galaxies [Not falsifiable:could not be proven false] - We are all playthings in a computer program created by advanced aliens - The laws of nature are magnificent and beautiful - The universe was created by God

Note that falsifiability alone does not make something science. However, scientific models must make predictions that can be tested, and in general we can only test claims or predictions that are falsifiable.

An important line of hydrogen occurs at a rest wavelength (as measured in a laboratory) of 656 nmnm (a nanometer (nmnm) is a billionth of a meter). Each diagram below has this line labeled with its wavelength in the spectrum of a distant star. Rank the motion of the stars along our line of sight (radial motion) based on their speed and direction, from moving fastest toward Earth, through zero (not moving toward or away from Earth), to moving fastest away from Earth

Notice that your correct answer ranks the stars in wavelength order. The first two stars are moving toward us, because their lines have wavelength shorter than the rest wavelength of 656 nm. The last two stars are moving away from us, because their lines have wavelength longer than the rest wavelength of 656 nm.

Which of the following procedures would allow you to make a spectrum of the Sun similar to the one shown, though with less detail?

Pass a narrow beam of sunlight through a prism. (The prism bends different wavelengths of light by different amounts, causing the white light from the Sun to spread out into a rainbow of colors. Absorption features appear as dark lines against the brighter background of the spectrum.)

Listed following are distinguishing characteristics and examples of reflecting and refracting telescopes. Match these to the appropriate category.

Reflecting Telescopes: most commonly used by professional astronomers today, The Hubble Space Telescope, world's largest telescope Refracting Telescopes:The world's largest is 1-meter in diameter, Galileo's telescopes, very large telescopes become "top- heavy", incoming light passes through glass

Which of the following best describes why the Sun's spectrum contains black lines over an underlying rainbow?

The Sun's hot interior produces a continuous rainbow of color, but cooler gas at the surface absorbs light at particular wavelengths. [The Sun's spectrum is an absorption line spectrum, which is produced when continuous light from a hot source (the Sun's interior) passes through a cooler cloud of gas (the gas that makes up the Sun's visible surface).]

How much greater is the light-collecting area of a 6-meter telescope than a 3-meter telescope?

The light-collecting area would be 4x greater on a 6-meter (which has 36) telescope than a 3-meter telescope (which has 9). The resolution of the 6-meter telescope would be half that of the 3-meter telescope because of the resolution formula.

One tidal bulge faces toward the Moon because that is where the gravitational attraction between Earth and the Moon is strongest. Which of the following best explains why there is also a second tidal bulge?

The second tidal bulge arises because gravity weakens with distance, essentially stretching Earth along the Earth-Moon line.

Any spectrum can be displayed either in photographic form as shown to the left or as a graph. Which of the following graphs could represent a portion of the Sun's visible light spectrum?

The smooth part of the curve represents the graph of the background rainbow of color; the dips in the curve represent the black lines where light is missing from the rainbow.

The Hubble Space Telescope obtains higher-resolution images than most ground-based telescopes because it is:

above Earth's atmosphere

If our eyes were sensitive only to X rays, the world would appear __________.

dark because X-ray light does not reach Earth's surface

Conservation of angular momentum and energy keeps the planets from falling into the Sun. (T/F)

false

Consider the statement "There's no gravity in space." This statement is:

false

Gravity is the strongest force in the universe. (T/F)

false

Newton's three laws of motion only apply on Earth. (T/F)

false

There is no gravity in space, so astronauts in the International Space Station float freely around the station. (T/F)

false

To make a rocket turn left, you need to:

fire an engine that shoots out gas to the right.

The gravitational potential energy of a contracting interstellar cloud

gradually transforms into other forms of energy. Submit

If you had only one telescope and wanted to take both visible-light and ultraviolet pictures of stars, where should you locate your telescope?

in space

Some nitrogen atoms have seven neutrons and some have eight neutrons. These two forms of nitrogen are:

isotopes of each other.

In the illustration of the solar spectrum, the upper left portion of the spectrum shows the __________ visible light.

lowest frequency [Red light is the longest wavelength visible light, and longer wavelength means lower frequency (because wavelength×frequency=speed of light wavelength×frequency=speed of light).]

Compared to their values on Earth, on another planet your

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

Would an x-ray telescope on an airplane be useful?

no

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

one-quarter as strong.

A spectral line that appears at a wavelength of 321 nm in the laboratory appears at a wavelength of 328 nm in the spectrum of a distant object. We say that the object's spectrum is:

redshifted