Stars & Galaxies Chapter 5 & 6

Currently, the largest optical telescope mirrors have a diameter of

10 m

An atom of the element iron has an atomic number of 26 and an atomic weight of 56. If it is neutral, how many protons, neutrons, and electrons does it have?

26 protons, 30 neutrons, 26 electrons

Suppose you look at a spectrum of visible light by looking through a prism or diffraction grating. How can you decide whether it is an emission line spectrum or an absorption line spectrum?

An emission line spectrum consists of bright lines on a dark background, while an absorption line spectrum consists of dark lines on a rainbow background

Without telescopes or other aid, we can look up and see the Moon in the night sky because it

reflects visible light

What is the purpose of interferometry?

It allows two or more small telescopes to achieve the angular resolution of a much larger telescope.

What is the purpose of adaptive optics?

It reduces blurring caused by atmospheric turbulence for telescopes on the ground.

What do astronomers mean by light pollution?

Light pollution refers to lights from human sources that make it difficult to see the stars at night.

Which of the following statements about X rays and radio waves is not true?

Neither X rays nor radio waves can penetrate Earth's atmosphere

Suppose we see two stars: a blue star and a red star. Which of the following can you conclude about the two stars? Assume that no Doppler shifts are involved.

The blue star has a hotter surface temperature than the red star

Which of the following is always true about images captured with X-ray telescopes?

They are always shown with colors that are not the true colors of the objects that were photographed

Which of the following best describes the fundamental difference between two different chemical elements (such as oxygen and carbon)?

They have different numbers of protons in their nucleus

The Chandra X-ray observatory must operate in space because

X rays do not penetrate Earth's atmosphere

Which of the following statements about thermal radiation is always true?

a hot object emits more X rays than a cool object

What is an artificial star?

a point of light in Earth's atmosphere created by a laser for the purpose of monitoring atmospheric fluctuations

Which of the following statements about electrical charge is true?

a positive charge and a negative charge will attract each other

According to the laws of thermal radiation, hotter objects emit photons with _________.

a shorter average wavelength

If we say that a material is opaque to ultraviolet light, we mean that it _________.

absorbs ultraviolet light

The frequency of a wave is

all of the above

An electron-volt is

an amount of energy much smaller than a joule.

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

Consider an atom of carbon in which the nucleus contains 6 protons and 7 neutrons. What is its atomic number and atomic mass number?

atomic number = 6, atomic mass number = 13

Which of the following wavelength regions cannot be studied with telescopes on the ground?

both B and C

Which of the following statements about electrons is not true?

electrons orbit the nucleus rather like planets orbiting the Sun

When an electron in an atom goes from a higher energy state to a lower state, the atom

emits a photon of a specific frequency

From shortest to longest wavelength, which of the following correctly orders the different categories of electromagnetic radiation?

gamma rays, X rays, ultraviolet, visible light, infrared, radio

Spectra from neutral atoms compared with spectra from ionized atoms of the same element

have different sets of spectral lines

The spectra of most galaxies show redshifts. This means that their spectral lines

have wavelengths that are no longer than normal

Which of the following objects is not a close approximation of a thermal emitter?

hot, thin gas

Which forms of light are lower in energy and frequency than the light that our eyes can see?

infrared and radio

An atom that has fewer electrons than protons is called a/an _________.

ion

When an atom loses an electron, it becomes

ionized

Which of the following is not an advantage of the Hubble Space Telescope over ground-based telescopes?

it is closer to the stars

How can an electron in an atom lose energy to go from a higher energy level to a lower energy level?

it releases a photon equal in energy to its own energy drop

How are wavelength, frequency, and energy related for photons of light?

longer wavelength means lower frequency and lower energy

How many atoms fit across the period at the end of this sentence?

millions

A gas heated to millions of degrees would emit

mostly X rays.

Compared to the size of its nucleus, the size of the atom is about

one hundred thousand times greater

When considering light as made up of individual pieces, each characterized by a particular amount of energy, the pieces are called

photons

Why do astronomers need different telescope designs to observe across the electromagnetic spectrum?

photons of different energy behave differently and require different collection strategies

Thermal radiation is defined as

radiation with a spectrum whose shape depends only on the temperature of the emitting object

In what part of the electromagnetic spectrum do the biggest telescopes on Earth operate?

radio

From lowest energy to highest energy, which of the following correctly orders the different categories of electromagnetic radiation?

radio, infrared, visible light, ultraviolet, x rays, gamma rays

We can see each other in the classroom right now because we

reflect visible light

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

telescopes can collect far more light with far better angular resolution

How does light-collecting area of an 8 meter telescope compare to that of a 2 meter telescope?

the 8 meter telescope has 16 times the light collecting area of the 2 meter telescope

Consider an atom of gold in which the nucleus contains 79 protons and 118 neutrons. What is its atomic number and atomic mass number?

the atomic number is 79, and the atomic mass number is 197

The wavelength of a wave is

the distance between two adjacent peaks of the wave.

Everything looks red through a red filter because

the filter transmits red light and absorbs other colors.

If we observe one edge of a planet to be redshifted and the opposite edge to be blueshifted, what can we conclude about the planet?

the planet is rotating

From laboratory measurements, we know that a particular spectral line formed by hydrogen appears at a wavelength of 121.6 nanometers (nm). The spectrum of a particular star shows the same hydrogen line appearing at a wavelength of 121.8 nm. What can we conclude?

the star is moving away from us

Suppose you want to know the chemical composition of a distant star. Which piece of information is most useful to you?

the wavelengths of spectral lines in the star's spectrum

Which of the following is not a good reason to place observatories on remote mountain tops?

to be able to observe at radio wavelengths

If a material is transparent, then it

transmits light well

The stars in our sky twinkle in brightness and color because of

turbulence in earth's atmosphere