Mastering Astronomy Unit 3 (Chapter 5 and 6)

Suppose you want to determine the chemical composition of a distant planet or star. Which of the following will be most useful to have?

high spectral resolution

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

infrared and radio

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

infrared light Its location in space allows it to observe infrared wavelengths that do not penetrate our atmosphere to the ground.

What is the wavelength of a radio photon from an "AM" radio station that broadcasts at 1400 kilohertz? What is its energy?

lambda=210m E=9.3x10^-28 J

Choose the correct definition of a molecule.

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

Rank the forms of light from left to right in order of increasing speed. To rank items as equivalent, overlap them.

All the same: uv, gamma, x, light, red, radio

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 absorption line spectrum shows what we see when we look at a hot light source (such as a star or light bulb) directly behind a cooler cloud of gas. Suppose instead that we are looking at the gas cloud but the light source is off to the side instead of directly behind it. In that case, the spectrum would __________.

be an emission line spectrum

Rank the forms of light from left to right in order of increasing frequency. To rank items as equivalent, overlap them.

radio waves infrared visible light ultraviolet X rays gamma rays Notice that the frequency order is the opposite of the wavelength order from Part A. You can understand why if you recall that wavelength times frequency always equals the speed of light. Because the speed of light is a constant, longer wavelengths must mean lower frequencies, and vice versa.

What type of visible light spectrum does the Sun produce?

an absorption line spectrum

An important line of hydrogen occurs at a rest wavelength (as measured in a laboratory) of 656 nm (a nanometer (nm) 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.

(1.) 646 nanometers. (2.) 650 nanometers. (3.) 656 nanometers. (4.) 657 nanometers. (5.) 663 nanometers.

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?

(Smooth up and down dips)

If your bill says you used 600 kilowatt-hours, how much energy did you use in joules?

2.16x10^9 J

Finding for Keck telescope light collecting

3.14xDistance^2/ 4

Your electric utility bill probably shows your energy use for the month in units of kilowatt-hours. A kilowatt-hour is defined as the energy used in 1 hour at a rate of 1 kilowatt (1,000 watts); that is, 1 kilowatt-hour = 1 kilowatt × 1 hour. Use this fact to convert 1 kilowatt-hour into joules

3.60×10^6 J

How much greater is the light-collecting area of one of the 10-meter Keck telescopes than that of the 5-meter Hale telescope?

4

Suppose observers at Earth's North Pole and South Pole use a transit of the Sun by Venus to discover that the angular diameter of Earth as viewed from Venus would be 62.8 arcseconds. Earth's radius is 6378 km.Estimate the distance between Venus and Earth in km and AU.

4.2×107 kmk m

Shown following are the primary mirror arrangements and total light-collecting area of five different telescopes. Notice that although the arrangements look similar to those in Part B, the light-collecting areas are not the same. Also listed is an amount of time (exposure time) that each telescope will be pointed at the same distant galaxy. Again assume that the quality of these mirrors, the detectors, and the observing conditions are identical. Rank the telescopes from left to right based on the brightness of the image each telescope will take of the galaxy in the time indicated, from brightest to dimmest. To rank two (or more) telescopes as equal, drag one on top of the other(s).

All are equal As your answer correctly indicates, it is the product of the light-collecting area and the exposure time that determines the total amount of light collected from a distant object.

Shown following are the primary mirror arrangements and total light-collecting area of five different telescopes. Each mirror uses a different segmented arrangement, but assume that they are all equivalent in quality and in their ability to focus light. Also assume that the telescopes use identical detectors and have the same observing conditions. Rank the telescopes from left to right based on their ability to detect very dim objects, from greatest to least. To rank two (or more) telescopes as equal, drag one on top of the other(s).

All equal If all else is equal (such as mirror quality, detector, and observing conditions), the ability to detect dim objects depends only on light-collecting area. Because all the telescopes shown have the same light-collecting area, they all can detect dim objects equally well. The arrangement of the mirrors does not matter, as long as they are arranged and shaped so they bring light to a perfect focus.

The circles in the diagrams below represent energy levels in an atom, and the arrows show electron (blue dot) transitions from one energy level to another. (The spacing between circles represents differences in energy: A larger spacing means a greater difference in energy.) Assuming that the transitions occur as photons are emitted, rank the atoms based on the photon energy, from highest to lowest.

As your answer correctly shows, the emitted photon must have exactly the same amount of energy that the electron loses in moving from the higher to the lower energy level. Therefore the ranking of the photon energies must be in the same order as the amounts of energy lost by the electrons, and longer arrows mean greater changes in energy.

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.

Wavelength from energy formula

E= hc/ lambda 6.626x10^-34x2.998x10^8/ wavelength

Jupiter Most of the surface of ____________ is covered with liquid water.

Earth

The diagrams below are the same as those from Part A. This time, rank the atoms based on the wavelength of the photon emitted as the electrons change energy levels, from longest to shortest.

From Part A, you already know the ranking of the photons by energy. Because higher energy means shorter wavelength, you have correctly found that the ranking for Part B is the reverse of that from Part A.

Sort each of the astronomical questions below into the appropriate bin based on the type of observation you would need to perform to answer it.

Imaging: How large is the Andromeda Galaxy? What are the major surface features of Mars? Are stars in the Orion Nebula surrounded by gas? Spectroscopy: What is the chemical composition of the Crab Nebula? What is the temperature of Jupiter's atmosphere? Is the star Vega moving toward us or away from us? Timing: Does the star Mira vary in brightness? Is the X-ray emission from the galactic center steady or changing? The three questions that require imaging are ones in which we are actually looking for something, while the two that require time monitoring both involve how something changes with time. We use spectroscopy to learn about chemical composition, temperature, and Doppler shifts that tell us about an object's motion.

Which of the following statements about Pluto is true?

It has more in common with comets in the Kuiper belt than it does with terrestrial planets like Earth

The planet that orbits closest to the Sun is________

Mercury

___________is about 30 times as far from the Sun as our own planet.

Neptune

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.

The planet with the lowest average density is________

Saturn

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.

What does angular resolution measure?

The angular size of the smallest features that the telescope can see.

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.

Choose the correct description of how deeply each portion of the electromagnetic spectrum penetrates Earth's atmosphere and if space telescopes are important to our understanding of the universe.

The only wavelengths that make it all the way to the ground are the narrow range of visible light (and a very small amount of the ultraviolet that is nearest in wavelength to visible light) and the radio wavelengths. A few other wavelengths can be detected from high mountains or from aircraft, but in order to observe most wavelengths,we must put telescopes in space, which is why space-based astronomy is so important.

Suppose you watch a leaf bobbing up and down as ripples pass it by in a pond. You notice that it does two full up and down bobs each second. Which statement is true of the ripples on the pond?

They have a frequency of 2 hertz.

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.

Study the graph of the intensity of light versus wavelength for continuous spectra, observing how it changes with the temperature of the light bulb. Recall that one of the laws of thermal radiation states that a higher-temperature object emits photons with higher average energy (Wien's law). This law is illustrated by the fact that for a higher temperature object, the graph peaks at __________.

a shorter wavelength

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

above Earth's atmosphere.

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

lowest frequency

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

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.

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.

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

visible light radio waves Both visible light and radio waves pass almost freely through Earth's atmosphere, and therefore are easily observed with ground-based telescopes. The only other light that can be observed with ground-based telescopes is infrared, but it can be detected only at high altitudes (such as mountaintops) and even then only in selected portions of the infrared spectrum.

wavelength equation

λ=c/f (speed of sound), (frequency)

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.

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.

The diagrams below show the same set of energy levels as in Parts A and B, but with a different set of electron transitions (notice that the arrows are now different). Assuming that these electron transitions were caused by the absorption of a photon, rank the atoms based on the energy of the absorbed photon, from highest to lowest.

As your answer correctly indicates, the atom in which the electron leaves (the atom is ionized) corresponds with the highest-energy photon, and the atom with the shortest arrow indicates the case where the absorbed photon had the lowest energy.

Each of the following statements describes an astronomical measurement. Place each measurement into the appropriate bin based on the type of telescope you would use to make it.

Infrared telescope: Determine the surface temperature of Venus. Steady a dense cloud of cold gas in space. Visible Light telescope: Obtain a spectrum of the sunlight reflected by Mars. Measure the brightness of a star that is similar to our Sun. X-ray telescope: Observe the hot (1-million K) gas in the Sun's corona. Look for high-energy radiation from a supernova. Cool objects emit in the infrared. The Sun and similar stars emit mostly in the visible; reflected light from Mars is therefore also visible light. Very hot gas emits X rays, which have very high energy (with only gamma-ray photons having more energy for light).

Listed following are the names and mirror diameters for six of the world's greatest reflecting telescopes used to gather visible light. Rank the telescopes from left to right based on their light-collecting area from largest to smallest. For telescopes with more than one mirror, rank based on the combined light-collecting area of the mirrors.

Largest> Large . Binocular Telescope (Two 8.4-m mirrors) Keck I (One 10-m mirror) Hobby-Ebberly (One 9.2-m mirror) Subaru (One 8.3-m mirror) Gemini North (One 8-m mirror) Magellan II (One 6.5-m mirror) >Smallest Larger mirrors have a larger light-collecting area. Remember that the light-collecting area is proportional to the square of the mirror diameter. For example, if Mirror A has twice the diameter of Mirror B, then Mirror A has 2x2 = 4 times the light-collecting area of Mirror B.

The only rocky planet to have more than one moon is _________

Mars

This photograph was taken on the surface of another world in our solar system. What world is it?

Mars

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.

Listed following are various physical situations that describe how light interacts with matter. Match these to the appropriate category.

Transmission: Visible light meets clear glass. Cell phone signals pass through walls. Absorption: Visible light does not pass through a black wall. Blue light hits a red sweatshirt. Reflection or scattering: Red light hits a red sweatshirt.White light hits a white piece of paper. Emission: Light comes from your computer screen. Light comes from a light bulb.

_________has a rotational axis that is tilted so much it lies nearly in the plane of its orbit.

Uranus i

________is the planet with the highest average surface temperature.

Venus.

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

dark because X-ray light does not reach Earth's surface Because X rays from the Sun do not reach Earth's surface, eyes that were sensitive only to X rays would have nothing to see.

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 While visible light can be observed from the ground, ultraviolet light can be easily observed only from space. Indeed, the capability of observing ultraviolet light is a major advantage of the Hubble Space Telescope over larger ground-based telescopes.

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.

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.

Click "show" for the emission line spectrum, then click "choose gases" and study the emission line spectrum for neon. The neon "OPEN" sign appears reddish-orange because __________.

neon atoms emit many more yellow and red photons than blue and violet photons

Thermal radiation is defined as _________.

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

We divide the electromagnetic spectrum into six major categories of light, listed below. Rank these forms of light from left to right in order of increasing wavelength. To rank items as equivalent, overlap them.

radio waves infrared visible light ultraviolet X rays gamma rays Notice that these wavelengths span an enormous range. The wavelengths of gamma rays can be smaller than the size of an atomic nucleus, while the wavelengths of radio waves can be many meters (or even kilometers) long. Visible light spans only a very narrow range of wavelengths, from about 400 nanometers at the blue (violet) end to about 700 nanometers at the red end.

Rank the forms of light from left to right in order of increasing energy. To rank items as equivalent, overlap them.

radio waves infrared visible light ultraviolet X rays gamma rays

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.