Module 5 HW 30/30

Study the figure, which shows how someone on Earth can view Jupiter's moon's eclipses when Earth is closer to or farther from Jupiter, and determine which of the following are correct.

-If light has infinite speed, an eclipse would be seen to happen at the same time regardless of how far away Earth is from Jupiter. -If light has finite speed, it would take longer for it to travel from Jupiter to Earth when Earth is farther from Jupiter.

In a vacuum, light travels 300,000 km every second. Examine the following figure, which shows how long it takes for light to travel particular distances, and then scroll down to the question at the end. Based on the time frames given in the above figure, which of the following are implications of the finite speed of light? Could be more that one correct answer. Based on the time frames given in the above figure, which of the following are implications of the finite speed of light?

-If the light of the Sun were suddenly extinguished, we wouldn't notice it from Earth for over 8 minutes. -There would be a noticeable delay in communications at the speed of light between Earth and astronauts on the Moon. -When we gaze at the Andromeda Galaxy, we are looking back in time to the way it used to appear millions of years ago.

Which of the following can astronomers determine directly from the spectrum of an object?

-Temperature -Speed toward or away from an observe -Composition

One emission line of hydrogen occurs at λ_rest=656.3 nm. Suppose you observe this emission line occurring at different wavelengths in four different stars. Which emission line corresponds with the star that is moving the fastest?

659.3 nm

Electrons prefer to be in the lowest ground state energy level and will therefore spontaneously fall back to this state when excited, releasing the excess energy in the form of light emitted in a random direction. Given this, what would observer 2 (who does not see the star through the gas) observe in the spectrum of the cloud of gas in the picture above? Select the appropriate spectrum below.

A

Select the spectrum that most closely matches the one you would expect to observe from the light source at the end of the Explanation in the AstroTour, after the light has passed through the hypothetical gas.

A

Suppose you observe four stars to have four different Doppler shifts, indicating four different radial velocities. Which star is moving the fastest?

Star 𝛽, 𝑣_𝑟=−50 𝑘𝑚/𝑠

How does the spectrum of a distant star reveal the star's chemical composition?

Dark lines, also called absorption lines, within the spectra are "fingerprints" for the different atoms and molecules within a star's atmosphere

As wavelength increases, the energy of a photon __________ and its frequency __________.

Decreases; decreases

Suppose you have a very hot cloud of gas that is in the process of cooling down. What type of spectrum would you observe?

Emission

Which part of the electromagnetic spectrum has the highest frequency?

Gamma

The nature of light is rather unique: It acts like both a particle (called a photon) and a wave that can propagate energy even through empty space. Choose all of the effects that would automatically happen if the wavelength of light were increased.

-The frequency of the light would decrease -The energy of the light would decrease

Astronomers may describe certain objects as being redshifted or blueshifted. Select all true statements about this phenomenon from those listed below.

-These objects are exhibiting the Doppler effect -Wavelengths of light from the objects differ from expected (rest) wavelengths because the object is moving away from (redshifted) or toward (blueshifted) the observer

Identify where each type of light belongs on the electromagnetic spectrum

1 - E. Radio wave 2 - G. Infrared 3 - F. UV light 4 - D. Gamma Ray

Rank the following in order of decreasing wavelength.

1. Radio waves 2. Infrared 3. Visible 4. Ultraviolet 5. Gamma rays

When an electron moves from a higher energy level to a lower energy level in an atom

A photon is emitted

Which star is hottest?

A star that radiates mostly blue light

Refer to the spectrum of hydrogen in the figure above. Why is the excited hydrogen gas in the image of Gum 41 glowing red?

Because of its atomic structure, hydrogen gas has a transition between excited states that produces red light

Why are the young stars blue?

Because they are relatively hot stars

When you look at the sky on a dark night and see stars of different colors, which are the hottest?

Blue

The bright, colorful "stripes" of a rainbow such as the one shown here follow a particular order. Rank each color of the rainbow by how much energy is carried by its electromagnetic waves, from highest to lowest.

Blue - 1. Most energy Yellow - 2 Orange - 3 Red - 4. least energy

The image provided shows a light source moving relative to three different observers: Fred, Velma, and Daphne. If the light source is emitting green light and moving with sufficient speed, identify which colors each person could possibly see.

Fred - Red light Velma - Blue light Daphne - Green light

How do we know the Sun is made of mostly hydrogen, instead of mostly carbon?

Hydrogen produces unique absorption lines in the Sun's spectrum that no other element can

Doubling a star's temperature will change its flux by how much?

It will increase 16 times as much

Suppose the Earth were to suddenly move to twice its current distance from the Sun. How would the energy received from the Sun change?

It would decrease by ¼

When you turn on a lightbulb in a room, the entire room appears to flood with light at the same time. Your eyes cannot perceive light originating at the bulb and then moving outward from it. This either means that light has infinite speed (appears everywhere instantaneously), or it moves so fast that it is difficult to tell the difference. How might you improve your chances of detecting the motion of light if it moves at finite speed?

Move farther away from the light source

Two stars are of equal luminosity. Star A is 3 times as far from you as star B. Star A appears _________ star B.

One-ninth as bright as

When less energy is radiated from a terrestrial planet, its __________ increases until a new __________ is achieved.

Temperature; equilibrium

Observations of excited gas in the lab show that every element, molecule, and ion has its own unique set of possible electron energy levels, as shown in the emission spectra below. Based on this fact, what can we find from the wavelengths of absorption lines seen in the spectrum of a star?

The composition of any gas between the light-emitting "surface" of the star and the observer

What distinguishes one element (such as hydrogen) from a different element (such as carbon)?

The number of protons in the nucleus