UWM Astronomy 103- Exam 2
Assume that a star behaves as a blackbody. If the temperature of that star doubles, then the peak wavelength of the radiation from the star will be ______ times the original wavelength.
0.5
Two important things a wavelength will tell you:
1. Hotter objects have more radiation at all wavelengths. 2. The radiation from hotter objects peaks at shorter wavelengths.
What can we learn from an objects light?
1. If the object radiates a continuous spectrum like a blackbody, we can determine its temperature 2. From an object's absorption or emission spectrum we can determine its elemental composition 3. If the object is moving toward or away from us, from the Doppler effect we can measure its speed
The atmosphere limits how clearly we can see from Earth. How can we solve this problem?
1. Put telescopes on mountains 2. Fix it with adaptive optics 3. Put telescopes in space
Human body temperature is roughly 300K. Model the body as a blackbody. At what wavelength would people radiate the most energy?
10^4 nm
The two brightest stars in the constellation Orion are the red star Betelgeuse and the blue star Rigel. The temperature of Betelgeuse is 1/3 of the temperature of Rigel. The peak wavelength of the radiation from Betelgeuse is ______ times the peak wavelength of the radiation from Rigel.
3
Plutoids
Balls of ice and rock in the Kuiper belt
When source light is moving toward you, its light is:
Blueshifted
Which terrestrial planets have magnetic field and which don't?
DO: Earth and Mars DON'T: Mercury and Venus
Which terrestrial planets have moons? Which don't?
DO: Earth and Mars DON'T: Mercury and Venus
The surface of Venus is mostly low density rock, but the average density of Venus is similar to that of Earth. The interior of Venus is therefore:
Denser than the average density of Earth
The following statement about the terrestrial planets is false:
Earth's atmosphere allows the Sun's infrared radiation in but doesn't allow much visible light to escape, resulting in the greenhouse effect.
11. Will the light given off by Earth's surface easily travel back through the atmosphere to space, or will it be absorbed by molecules in the atmosphere?
Earth's surface gives off infrared light, much of which is absorbed by the atmosphere. This means that it will not easily travel back through the atmosphere and out into space.
The Sun is approximately 6000 K at the surface and has an energy distribution that peaks at visible wavelengths; Earth's surface is much cooler at about 288 K. What type of light do you think Earth's surface primarily gives off: ultraviolet, visible, or infrared?
Earth's surface primarily gives off infrared radiation. It is cooler than the surface of the Sun, which has an energy distribution that peaks at visible wavelengths, so its energy distribution must peak at longer wavelengths. Among the three choices, only infrared light has longer wavelengths than visible light.
Compared to the largest earthbound telescopes, the Hubble space telescope has:
Finer resolution
Mars
Half the radius of Earth Mass is 10% of Earths Thin atmosphere Extinct volcanoes Called red planet because of its iron oxide reactions (rust) Has permanent caps which contain frozen water Canyons Used to be hot, cooled down
Mercury's atmosphere is weak or nonexistent because of its: I. small mass II. high density III. high surface temperature
I and III
Comets
Ice and rocks
Advantage of space telescopes:
Images are not blurred by the atmosphere
Which TWO forms of light account for the majority of energy coming from the Sun: ultraviolet, visible, or infrared?
Infrared and visible light account for most of the energy. Infrared has the largest share at 48%, and visible accounts for 44%.
Comparing visible and infrared light, which experiences more absorption?
Infrared light experiences more absorption.
Comparing ultraviolet and infrared light, which would you say has an easier time getting through our atmosphere?
Infrared light gets through the atmosphere more easily than ultraviolet light.
You are gradually heating a lump of rock in an oven to an extremely high temperature. As it heats up, the lump emits nearly perfect blackbody radiation, meaning that it:
Is both brighter and bluer when hotter
The surface of Mercury:
Is heavily cratered because it is geologically long dead
What are adaptive optics?
It is.a simulator with a laser that excites sodium atoms in the upper atmosphere to create an "artificial star." It monitors distortions of atmosphere by looking at changes in image of the artificial star.
If a terrestrial planet were to have a cratered surface like the Moon's what would you conclude about the planet?
It must have little or no atmosphere.
Why does Mars appear red-orange?
Its rocks have suffered "rusting" and contain reddish-orange iron oxides.
What does a photons ability to be absorbed by Earths surface depend on?
Its wavelength
Name the Jovian planets and some properties:
Jupiter, Saturn, Uranus, Neptune Made of gases, have a lower density, are larger
Compared to terrestrial planet, all Jovian planets are:
Larger and less dense
Due to the light absorbed by Earth's surface that was emitted by Earth's atmosphere, is Earth's temperature near the surface going to be warmer or cooler than it would be without this absorbed light?
Light absorbed by Earth's surface that was emitted by Earth's atmosphere makes the tem- perature near the surface warmer than it would be without this light. Light absorbed from the atmosphere accounts for a large fraction of the energy that heats the Earth.
Which of the terrestrial planets have atmospheres?
Mars, Venus, and Earth
What is the primary method that scientist use to study the interior structure of the Earth?
Measuring the speed of seismic waves (earthquaked) and determining whether or not they pass through Earth
Name the terrestrial planets and some properties:
Mercury, Venus, Earth, Mars They are made of rock, have a high density, and are relatively small
How does the music on your phone get communicated to your earbuds so that you can listen to your Pandora playlist while jogging on the treadmill? First your music is converted into a signal that can be sent to your earbuds. That signal is light, and bluetooth uses light with a frequency of about 2.45 Gigahertz, which is 2.45x10^9 Hz, to transmit the encoded music. When your earbuds "see" that light, they then re-convert the encoded information into an audio signal that you can hear. According to Table 5.1 from the book, what type of light is Bluetooth using? You may find helpful that the speed of light is about 3x10^8 meters per second.
Microwaves
NASA's Jet Propulsion Laboratory (JPL) in Pasadena California is the central hub of the "Deep Space Network," a network of telescopes used for communicating with all of our satellites and spacecraft we have sent around our solar system. All communication is achieved by encoding messages in light waves and emitting those light waves at our satellites. These satellites have their own "telescopes" which "see" the messages (i.e. antenna). To design an effective Earth based communication network, what is the best type of light we should use for communication? It should be ideally low in energy, and must be able to transmit from the ground into space. (Hint: consider the effect our atmosphere has on telescopes).
Microwaves
The average density of the Earth is about:
Midway between the density of rock and the density of iron
When an electron in an atom emits light, it:
Moves closer to the nucleus
The Earth's atmosphere is primarily:
Nitrogen and Oxygen
Mercury
No atmosphere No volcanoes Has a magnetic field Extreme temperature difference
Which one of the following statements about the greenhouse effect, Earth, and Venus is false?
No greenhouse effect currently occurs on Earth, and this is a good thing for humans.
(b) Which of these three stars, if any, will give off light that appears to be redshifted? Explain your reasoning.
None of the stars will appear to be redshifted, since we are moving toward all of them.
Stars A, B, and C are moving toward Earth. Star A is a blue star that is closer to Earth than the other two. Star B is a red star that is the farthest away of the three. Star C is a yellow star halfway between Stars A and B.
None of the three
Auroras
Occur during heightened solar activity when the sun's charged particles break through Earth's magnetic field and hit the upper atmosphere.
Explain the process of how light is absorbed and emitted back into space.
Once visible light from the Sun reaches the surface of Earth, some of the light is reflected back toward space as visible light, and the remaining light is absorbed by the ground. Reflected light does not change the temperature of the surface, whereas absorbed light causes the temperature of the surface to increase. Earth's heated surface then gives off infrared light to Earth's atmosphere. As an example, on a hot day, black asphalt absorbs more visible light and gives off more infrared light than does a white crosswalk.
Why is ultraviolet light NOT an important energy source for heating the surface of the Earth?
Only a small fraction of the energy from the Sun is in the form of ultraviolet light, and most of this light is then blocked by the atmosphere.
Meteoroids
Pebbles from comets ejected when comets came close to the Sun, fragments of asteroids
How can you tell on a diagram that a star is moving faster than the rest?
Pick out the resting star, and compare it to the star that has the widest shift. (and for the opposite-aka slowest- it shows by which shift lines are closest to the star).
Radio telescopes are large in part to improve their resolution, which is poor because:
Radio light has a long wavelength
Which light form is observed by earthbound telescopes?
Radio waves and visible light
What do optical telescopes do?
Read into visible light emitted from space. It reads light from 400-700nm.
A star with a continuous spectrum shines through a cool interstellar cloud composed primarily of hydrogen. The cloud is falling inward toward the star (and away from Earth). Which best describes the spectrum seen by an Earthbound observer?
Red shifted absorption lines
Asteroids
Rocky, mostly between Mar and Jupiter
Give qualities of Venus:
Similar in mass of Earth About the same density as earth Very thick atmosphere Many volcanic features NO magnetic field Weak convection Atmosphere with clouds of sulfuric acid- traps heat via the greenhouse effect May have had water at some point and it evaporated
Which of the stars are giving off light that appears blueshifted on a number chart?
Since a blueshift is a shift to shorter wavelengths, all of the stars for which the line appears at wavelengths less than 656 nm are giving off blueshifted light.
Explain temperature in relation to wavelength:
The coldest objects give off the longest wavelengths, and the hottest objects have the shortest wavelengths.
When multiple radio telescopes are used for interferometry (linked together), resolving power is most improved by increasing
The distance between telescopes
What type of light (ultraviolet, visible or infrared) primarily heats Earth's surface and where does this light come from? What type of light primarily heats Earth's atmosphere and where does this light come from?
The figure shows that the largest portion of light absorbed by Earth's surface comes from the atmosphere (324 watts per square meter). This is infrared light. The figure also shows that most of the energy that heats the Earth's atmosphere is emitted by Earth's surface. This is also infrared light.
Compared to an atoms absorption lines, it's emission lines are:
The same wavelength
In the Sun, the transition of an electron from level 4 to level 2 of hydrogen produces light with a wavelength of 486.1 nm. In a star twice as hot as the Sun, this transition would produce photons with:
The same wavelength
Suppose that two observers look at the spectrum of a cloud of gas in a laboratory from different points of view. The first observer reports seeing emission lines from the cloud, and the second reports seeing absorption lines from the cloud. How can this best be explained?
The second observer sees the gas against a hot background
What is redshift?
The shifting of the lines in the spectrum of an object to longer wavelengths, due to its motion away from the observer. Long=Red
Resolving Power (resolution)
The smallest angle that can be seen with a given telescope. Larger telescopes have a higher resolution. The resolving power of all earthbound optical telescopes is limited by the turbulence of the air.
What causes light from a star to be Doppler-shifted?
The speed of the star toward or away from us
Which star is giving off light that appears shifted by the greatest amount? Is this light shifted to longer or shorter wavelengths on a number chart?
The star giving off light shifted by the greatest amount is the star in which the line appears farthest from 656 nm. To figure this out we calculate the difference from 656 nm for each of the stars.
One of the spectral lines of hydrogen has a laboratory wavelength of 656 nm. If you observe this line at a wavelength of 653 nm in the spectrum of a star, which of the following is true
The star is moving toward you
Which star is moving the fastest? Is it moving toward or away from the observer on a number chart?
The star that is moving fastest is the star with the largest shift. ts light is blueshifted to shorter wavelengths, and therefore it is moving toward the observer.
Most of the solar systems mass is in:
The sun
If you were going to design a pair of glasses for seeing animals at night, you would want them to convert:
infrared photons to optical photons
Rules to be a planet:
•Be in orbit around only the Sun •Have a nearly round shape, i.e. have enough mass that gravity has pulled it into a sphere •Have "cleared the neighborhood" around its orbit
What are the cons of refractors?
•Lenses are heavy, can only be supported at edges •Gather less light than mirrors •Light traveling through a lens is refracted differently depending on wavelength (chromatic aberration) •Lens needs two optically acceptable surfaces, mirror only needs one (but mirror surfaces have to be more precise) •Lenses tend to be more expensive
How do we measure the solar system?
•Planet rotation period known from observations •Rotation period + Kepler's laws gives us planet's distance from Sun •Planet radii known from angular size (using telescopes) •Planet masses known from Newton's laws •Density can be calculated knowing radius and mass
The following statements about terrestrial planets are true:
-Despite being one of the closest planets to the sun, some parts of Mercury have a surface temperature far below freezing point -Long ago, Mars probably had a thicker atmosphere than it does now, which sufficiently high temperatures and pressures to allow liquid water to exist on its surface. -Venus is the hottest planet in our solar system, mainly due to an elevated greenhouse effect. -Earth's atmosphere plays a central role in keeping our planet from freezing cold temperatures.
Jupiter
79 moons Mostly hydrogen and helium Multicolored bands in the atmosphere Bands are caused by convective cells that are stretched by rotation Most prominent feature is the Great Red Spot Belts are high and low pressure regions, which we also have on Earth Because of the Jupiter's rapid rotation and thick atmosphere, the belts stretch around the planet rather than being localized Jupiter's rapid rotation, strong convection and conducting metallic hydrogen give it a very strong magnetic field, 20,000 times stronger than that of Earth
Uranus
98 degree tilt
Consider two stars A and B. A is bright at ultraviolet (UV) wavelengths and dim in at infrared (IR) wavelengths, while B is dim in the UV and bright in the IR. Which star is hotter?
A
What is a blackbody?
A "blackbody" is an idealized object which absorbs all light. This causes the object to heat up and emit light based on its temperature. Nothing is a perfect black-body, but in astronomy blackbodies are good estimates for stars - the light they emit and their temperatures.
Nebula
A diffuse cloud of gas and dust
How did our solar system form?
A nebula attracts gravitationally (Newton's law of gravity) and begins to "coalesce." As the cloud coalesces it tends to start spinning. Most of the mass will go into a central star, but additional "seeds" can to form, which eventually become planets.
Which of the stars are giving off light that appears redshifted on a number chart?
A redshift is a shift to longer wavelengths, so all of the stars for which the line appears at wavelengths greater than 656 nm are giving off redshifted light.
Refraction telescope
A telescope that uses a converging lens to collect light. The large lens gathers and bends light, while the small lens magnifies and focuses light for your eyes.
Reflection telescopes
A telescope with a small mirror at the top that reflects light and image into eyepiece. The large mirror gathers and reflects light.
Imagine you observe a planet orbiting another star outside of our solar system, and that from your perspective, you are able to see the light from that star pass through the planet's surrounding atmosphere and into your telescope. Studying the ____ spectra of this filtered light should tell you about the atomic and molecular composition of that planet's atmosphere. (Note, astronomers today are actively attempting to perform measurements just like this of observed exoplanets to learn more about their atmospheres!).
Absorption
Is more energy absorbed by Earth's surface in the form of light coming from the Sun or from light emitted by Earth's atmosphere?
According to the figure, the amount of sunlight absorbed by the Earth's surface is 168 watts per square meter, and the amount of energy emitted by the atmosphere that is absorbed by Earth's surface is 324 watts per square meter. So the surface of the Earth absorbs more energy from the atmosphere than from the Sun.
Why are satellites used to detect x-rays?
Air absorbs x-rays
Compared to Jovian planets, terrestrial planets:
All spin slower
If an atom absorbs light:
An electron jumps to a higher energy level
If an atom emits light:
An electron jumps to a lower energy level
If an atom is ionized:
An electron leaves its atom
What is the Doppler shift?
An increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move toward (or away from) each other. The effect causes the sudden change in pitch noticeable in a passing siren, as well as the redshift seen by astronomers.
What is blueshift?
As source approaches you the wavelength gets shorter and lines in spectrum shift to the blue, frequency increases. Short=Blue
The plot above shows planets plotted according to their atmospheres' temperature and pressure, with the position of Earth shown by its photo. Which position marks Venus? A B Sun---------earth C D
B
What are the TWO greenhouse gases most responsible for absorbing infrared light in Earth's atmosphere?
Carbon Dioxide (CÓ) and Water Vapor (H2O)
The primary greenhouse gases in the Earth's atmosphere are:
Carbon dioxide and Water Vapor
Can you tell the color of the star from how it is moving?
The motion of a star makes only a small change in the wavelength of the light it emits, not enough to change its overall color. The color of a star is determined by its temperature, you can't tell from the color whether or not it's moving. You have to look at he shift in wavelength of the lines in the star's spectrum to determine whether it's moving toward or away from you.
Why do all of the planets have orbits that lie in nearly the same plane and that are in the same direction -- counterclockwise looking down on the solar system from far above the Earth's North Pole?
The planets and Sun all formed from a cloud of gas and dust that contracted as it cooled. As the cloud contracted, its spin increased and it flattened. By the time the planets formed, the cloud was a flat spinning disk.
How does the total amount of energy coming from the Sun compare to the total amount of energy leaving Earth to space?
The total amount of energy coming from the Sun is 342 watts per square meter. To figure out how much energy is leaving Earth to space, we need to add the contributions that are reflected from Earth's surface (30), reflected from Earth's atmosphere (77), emitted by Earth's surface (40), and emitted by Earth's atmosphere (195). Adding these numbers together gives 342 watts per square meter. So the total amount of energy coming from the Sun is the same as the total amount of energy leaving Earth to space.
Why is the following statement correct? Earth's visible light is just reflected sunlight. Earth's surface is much cooler than the Sun and mostly gives off energy closer to the kind that our bodies give off — infrared light. I think the surface radiates infrared light during both the daytime and the nighttime based on its temperature.
The visible light we see from the surface of the Earth is just reflected light from the Sun. The light the surface itself radiates is at longer wavelengths, corresponding to its temperature which is cooler than the Sun.
Why do we put telescopes on mountains?
To avoid some of the blurring effects of the atmosphere
Comparing ultraviolet and infrared light, which would you say experiences more absorption?
UV light experiences more absorption.
Which light form accounts for the least amount of energy coming from the Sun?
Ultraviolet light accounts for the least energy at 7%.
What gas molecules are primarily responsible for the absorption of each of the following types of light in our atmosphere?
Ultraviolet- Ó and Ǒ Visible- none Infrared- H2O, CÓ
Comparing visible and infrared light, which would you say has an easier time getting through our atmosphere?
Visible light has an easier time getting through our atmosphere.
What do you think would happen to the temperature of the Earth's surface if the amounts of water vapor and carbon dioxide in Earth's atmosphere were reduced?
Water vapor and carbon dioxide are the molecules in the atmosphere that absorb and re-emit infrared light, so if their amounts were reduced, the amount of energy absorbed and re-emitted by the atmosphere would decrease. This would remove some of the energy heating the Earth's surface, and its temperature would decrease.
c) Which of these three stars, if any, will give off light that appears to have no shift? Explain your reasoning.
We are moving toward all the stars, so no stars will appear to have no shift.
Imagine our solar system is moving toward a group of three stars. Star A is a blue star that is slightly closer to use than the other two. Star B is a red star that is farthest away from us. Star C is a yellow star that is halfway between Stars A and B. (a) Which of these three stars, if any, will give off light that appears to be blueshifted? Explain your reasoning.
We are moving toward all three stars, and therefore the light from all three stars, A, B and C, will be blueshifted. The Doppler shift depends only on how the observer and an object are moving with respect to each other, not on how far away the object is or on what color it is.
Neptune
Windy planet because of its crazy windspeed and long, huge storms
Does Earth's surface give off light at night?
Yes. Earth's surface gives off infrared light because of its temperature, which means that it also must radiate at night.
What determines the color of a star?
its temperature
Compared to visible light, radio waves have
lower energy and longer wavelength