Astronomy Ch. 5
Which of the following statements about thermal (or blackbody) radiation is always true.
A hot object emits more radiation per unit surface area than a cool object.
Recall one of the laws of thermal radiation stating that a higher-temperature object emits photons with a 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 -Wien's law states that the thermal radiation from a hotter object peaks at a shorter wavelength.
Notice the sun's spectrum appears brightest (or more intense) in the yellow-green region. This fact tell 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 temp of about 5800 K.
Which of the following statements is true of green grass?
-It absorbs the red light and reflects green light -(green lawn reflects (scatters) green but absorbs all other colors.
What are advantages to the Hubble Space Telescope overground-based telescopes?
-Stars do not twinkle when observed from space -It can observe infrared and ultraviolet light, as well as visible light. -It never has to close because of cloudy skies. NOT AN ADVANTAGE: it is closer to the stars-distance to the stars has absolutely nothing to do with it, as should be apparent if one considered the solar system and the distances to stars to scale.
Studying a spectrum from a star can tell us a lot. These following statements support this.
-The peak of the star's thermal emission tells us its temperature: hotter stars peak at shorter (bluer) wavelengths. -We can identify chemical elements present in the star by recognizing patterns of spectral lines that correspond to particular chemicals. -Shifts in the wavelengths of spectral lines compared to the wavelengths of those same lines measured in a lab on Earth can tell us the star's speed toward or away from us.
Which of the following is true about X rays and radio waves?
-X rays have a higher frequency than radio waves -X rays have shorter wavelengths than radio waves -X rays and radio waves are both forms of light, or electromagnetic radiation
What type of visible light spectrum does the Sun produce?
An absorption line spectrum -The sun can simplistically be pictured as a hot interior light source surrounded by a thin, cooler layer of gas (the Sun's photosphere). The interior produces a continuous spectrum, while the overlying gas acts like a cloud to produce absorption lines.
Each of the following describes an "Atom 1"and an "Atom 2". In which case are the two atoms different isotopes of the same element?
Atom 1: nucleus with 7 protons and 8 neutrons surrounded by 7 electrons Atom 2: nucleus with 7 protons and 7 neutrons surrounded by 7 electrons Because both atoms have the same atomic number but different atomic mass numbers.
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 lab. -Each chemical element (or ion or molecule) produces a unique set of spectral lines; the wavelengths of these lines can be measured in the lab. I f the sun's spectrum contains the set of lines for some particular element, we conclude that the sun contains that element. We determ. the sun's overall chem comp by ecamining all the lines in its spectrum.
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.
Betelgeuse is the bright red star representing the left shoulder of the constellation Orion. All the following statements about Betelgeuse are true. Which one can you infer from its red color?
Its surface is cooler than the surface of the Sun. -Red light has lower energy than yellow or white light, so the red color of Betelgeuse tells us that its peak thermal radiation comes at lower energy than the peak thermal radiation of the yellow/white sun. A lower energy of peak radiation means a lower temperature.
Why does neon appear based of the Emission Spectrum?
Neon atoms emit many more yellow and red photons than blue and violet photons. -The many more lines in the yellow and red parts of the spectrum are what make "pure" neon lights look red or orange. (When you see "neon lights" glowing with other colors (besides reddish-orange) it is generally because they contain additional elements (besides neon) making them glow. )
In a solar spectrum what color has the lowest frequency in visible light
Red light is the longest wavelength visible light and longer wavelength means lower frequency because wavelength x frequency = speed of light.
Supposed you built a scale-model atom in which the nucleus is the size of a tennis ball. About how far would the cloud of electrons extend?
Several kilometers
Suppose that the angular separation of two stars is 0.1 arcseconds, and you photograph them with a telescope that has an angular resolution of 1 arcsecond. How will the stars appear in the photograph?
Since their angular separation is smaller than the telescope's angular resolution, your photograph will seem to show only one star rather than two.
Suppose that Star X and Star Y both have redshifts, but Star X has a larger red shift than Star Y. What can you conclude?
Star X is moving away from us faster than Star Y.
Which of the following conditions lead you to see an absorption line spectrum from a cloud of gas in interstellar space?
The cloud is cool and lies between you and a hot star.
If an electron at level 1 in a hydrogen atom absorbs 10.2 eV of energy, it moves to level 2. What typically happens next?
The electron returns to level 1 by emitting an ultraviolet photon with 10.2 eV of energy. (Electron typically return to the ground state unless something interferes with this return.)
Lowest energy to highest energy:
The energy of a photon of light is proportional to its frequency: energy = Planck's constant x frequency
Which of the following best describes why we say that light is an electromagnetic wave?
The passage of a light wave can cause electrically charged particles to move up and down.
Passing a narrow beam of sunlight through a prism causes:
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.
From lab measurements, we know that a particular spectral line formed by hydrogen appears at a wavelength of 486.1 nanometers (nm). The spectrum of a particular star shows the same hydrogen line appearing at a wavelength of 486.0 nm. What can we conclude?
The star is moving towards us. -The wavelength is shifted from 486.1 to 486.0 nm, which means a shift to a shorter wavelength. A shorter wavelength means a shift to the blue end of the spectrum (a blueshift) so that the object is moving towards us.
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'd 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)
Studying a spectrum from a star can tell us a lot. 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. (We cannot measure radius from a spectrum without a lot of other info)
Which of the following is 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. -since "true colors" make sense only for visible light, not X rays.
The Chandra X-ray Observatory must operate in space because:
X Rays do not penetrate the Earth's atmosphere. -to detect X-rays, the observatory must be above Earth's atmosphere.
Which of the following statements about X rays and radio waves is NOT true?
X rays travel through space faster than radio waves because all light travels at the same speed.
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 what 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 spectrum -B/c the cloud absorbs light from the hot source, conservation of energy demands that it must re-emit light with the same total amount of energy. However, this re-emitted light is sent in all directions, not just along the direction from which it originally came. Therefore, if we view the cloud from a location from which we can see only the light that the cloud itself emits, we will see an emission line spectrum.
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.
Shortest wavelength to longest wavelength:
gamma rays, X-rays, ultraviolet, visible light, infrared and radio waves -the waves 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.
Lowest frequency to highest frequency:
radio waves, infrared, visible light, ultra violet, x-rays and 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. B/c the speed of light is a constant, longer wavelengths must mean lower frequencies and vice versa.
lowest speed to highest speed:
they all have the same speed -the speed of light is a constant (in empty space) for all forms of light, meaning that all forms of light travel at the same speed, regardless of wavelength, frequency, or energy
which of the following forms of light can be observed with telescopes at sea level?
visible light and 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.
