HW 5

If you heat a gas so that collisions are continually bumping electrons to higher energy levels, when the electrons fall back to lower energy levels the gas produces

an emission line spectrum.

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

four times

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

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

infrared light

If you see the color red in an X-ray image from the Chandra X-Ray Observatory, it means:

it depends: the colors are chosen arbitrarily to represent something about the X rays recorded by the telescope.

Thermal radiation gets its name because __________.

its spectrum depends on the temperature of the object emitting it

Compared to a cold object, a hotter object of the same size emits most of its light at __________ wavelengths and emits _____ light overall.

shorter, more

Notice the numbered points on this diagram of a reflecting telescope. Which point represents the place where the starlight is in focus?

1

Notice the numbered points on this photo of the Gemini North reflecting telescope. Where is the secondary mirror located?

3

Choose the correct definition of a molecule.

A molecule is a group of two or more atoms bound together.

Choose the correct definition of an atom's atomic mass number.

An atom's atomic mass number is the number of protons plus the number of neutrons.

Choose the correct definition of an atom's atomic number.

An atom's atomic number is the number of protons it has in its nucleus.

Most continuous spectra are examples of what we also call thermal radiation spectra. Why do we call them "thermal" spectra?

Because the peak wavelength of the spectrum depends on the temperature of the object producing the spectrum.

Most interstellar clouds are made mostly of hydrogen (because hydrogen is the most common element in the universe). Why are these clouds usually dominated by the color red?

Because the strongest visible emission lines from hydrogen are red.

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.

Under what circumstances can energy level transitions occur?

Electrons can make a transition from one level to another by taking in or emitting a specific amount of energy. If too much or too little energy is offered, the electron cannot make the transition.

Which of the following statements about electrons is not true?

Electrons orbit the nucleus rather like planets orbiting the Sun.

Comte was proven wrong in his claim that we could never learn the composition of stars. What do we know today that Comte did not know when making his claim, and that makes it possible for us to learn the chemical compositions of stars?

Every chemical element produces a unique spectral fingerprint

Why do incandescent bulbs require more energy to shine with the same amount of visible light as LED bulbs?

Incandescent bulbs emit most of their energy as infrared light.

Why does Mars appear reddish in color?

It reflects most of the Sun's red light while absorbing most of its blue light.

Imagine being on the Moon and looking at the thermal radiation spectrum of Earth. How would it compare to the spectra shown on the graph in the video?

It would be very similar to the spectrum of the human.

This diagram shows the approximate depths to which different wavelengths of light penetrate Earth's atmosphere. Why does it show an airplane?

Much of the infrared spectrum can be observed from an airplane that flies above most clouds

Choose the correct statement describing, what will you see if you look at them with a telescope that has an angular resolution of 0.5 arcsecond.

One point of light that is the blurred image of both stars.

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.

This X-ray image was taken by the Chandra X-ray Observatory. Without knowing anything more about the object that is shown, what can you conclude from looking at this image?

Some parts of the object emit more X rays than others

Which of the following statements best describes the two principal advantages of telescopes over eyes?

Telescopes can collect far more light with far better angular resolution.

What do you see orbiting Earth in this photo?

The Hubble Space Telescope

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 "extraordinary" part of Comte's claim was his statement that we could never learn the composition of stars. Which of the following best summarizes the key lesson we should learn from the fact that his claim was ultimately proven wrong?

The advance of science and technology may someday provide ways to answer questions that seem unanswerable today

Suppose that Mars had a higher surface temperature. How would its spectrum be different?

The peak in the infrared would be at shorter wavelength.

Consider a planet orbiting another star that is very similar to our Sun. Assume the planet is about the size of Earth and has an Earth-like orbit around its star. Which of the following statements are true about the light coming from the star and planet?

The planet emits virtually all its light as infrared light. The star emits much more total light than the planet. The star's spectrum peaks in visible light.

The first telescopic photo shows what appears to be a single star. The second photo shows the same object, now revealed to be two distinct stars. What is the difference between the two photos?

The second photo has better (smaller) angular resolution than the first photo.

This graph shows a light curve for a star. What can you conclude from this graph?

The star periodically dims and brightens, with a brightness peak about once a year.

We can learn a lot about the properties of a star by studying its spectrum. All of the following statements are true except one. Which one?

The total amount of light in the spectrum tells us the star's radius.

This photo shows a single star photographed by the Hubble Space Telescope. Why doesn't the star appear as a single, sharp point of light?

The wave properties of light make this type of blurring an unavoidable feature of any telescope.

Choose the correct conditions, under which two atoms are different isotopes of the same element

Two atoms having the same number of protons and different numbers of neutrons

What do we mean when we say that energy levels are quantized in atoms?

We mean that the electrons can have only discrete values of electrical potential energy in atoms

For an object producing a thermal spectrum, a higher temperature causes the spectrum to have ___________.

a peak intensity located at shorter wavelength

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

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

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

lowest frequency

The twinkling of stars is caused by:

motion of air in our atmosphere

What kinds of light are these telescopes designed to detect? (big ass white ones)

radio waves

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

This photo shows a satellite TV dish on a house. In essence, the dish is _________.

the primary mirror of a radio telescope

Which of the following could not be measured by an observation that uses only imaging?

the rate at which a variable star brightens and dims

Which of the following could not be determined by an observation that uses only spectroscopy?

the size of a distant galaxy

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

visible light radio waves