Astronomy Chapter 6, Chapter 6 Mastering Astronomy, stars and galaxies rveiew

11. What determines an atom's atomic number? Under what conditions are two atoms different isotopes of the same element? What is a molecule?

Number of protons, different isotopes because of different number of neutrons, molecules are formed when multiple atoms combine

Which of the following is not one of the three main categories of observation generally used by astronomers?

Filtering to look at just a single color from an object.

What do we mean by the diffraction limit of a telescope?

It is the angular resolution the telescope could achieve if nothing besides the size of its light-collecting area affected the quality of its images.

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.

9. List the different forms of light in order from lowest to highest energy. Would the list be different if you went in order from lowest to highest frequency? From shortest to longest wavelength? Explain

wavelength: gamma, x-rays, ultraviolet, visible, infrared, microwave, radio No, it would be the same if it were organized by frequency Yes, they would be backwards if they were organized by wavelength because the ones with higher frequency and energy have a shorter wavelength.

What is the angular resolution of the human eye?

about 1 arcminute, or 1/60 of a degree

Which technology can allow a single ground-based telescope to achieve images as sharp as those from the Hubble Space Telescope?

adaptive optics

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

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

To achieve the same angular resolution as a visible-light telescope, a radio telescope would need to be

in space

The twin 10-m Keck telescopes can work together to obtain better angular resolution through a technique known as __________.

interferometry

The twinkling of stars is caused by

motion of air in our atmosphere

The twinkling of stars is caused by:

motion of air in our atmosphere.

Where should you put a telescope designed for ultraviolet observations?

In Earth orbit

What do we need to know if we want to measure an object's mass with "Newton's version of Kepler's third law"?

-"Newton's version of Kepler's third law" allows us to calculate the mass of a distant object, if we measure the orbital period and distance of another object orbiting around it ex) We can measure the mass of the sun from Earth''s orbital period (1 year) and its average distance (1 AU)

20. Describe two ways in which the thermal radiation spectrum of an 8,000K star would differ from that of a 4,000 K star.

-An 8,000K star would emit a lot more light at every wavelength than the 4,000K- sometimes in places where the cooler star wont emit light at all-making it bluer. (shorter wavelengths). -Hotter star emits photons with a higher average KE (makes the peaks of the graph at shorter wavelengths for hotter objects).

Law of Conservation of Momentum

-As long as there are no external forces, the total momentum of interacting objects cannot change; that is, their total momentum is conserved. -An object can gain or lose momentum only if another object's momentum changes by a precisely opposite amount. Ex) In space, objects always move at same speed because there are no external forces

Law of Conservation of Angular Momentum

-As long as there is no external torque, the total angular momentum of a set of interacting objects cannot change -An objects angular momentum can change ONLY by transferring some angular momentum to or from another object. Ex) Earth constantly moves in the same orbit at the same speed because there is no external torque to change it.

Law of Conservation of Energy

-Energy can't appear out of nowhere or disappear to into nothingness. -Objects can gain or lose energy only by exchanging energy with other objects Ex) All actions on Earth involve exchanges of energy or the conservation of energy from one form to another.

Universal Law of Gravitation

-Every mass attracts every other mass through the force called Gravity -The strength of the gravitational force attracting any two objects is directly proportional to the product of their masses. ex) Doubling the mass of one object doubles the force of gravity between the two objects. -The strength of gravity between 2 objects decreases by the "square" of the distance between their centers ex) doubling the distance between two objects weakens the force of gravity by a factor of 2^2, or 4.

Explain why orbits cannot change spontaneously, and how a "gravitational encounter" can cause a change. How can an object achieve "escape velocity"?

-Orbits cannot change spontaneously, UNLESS another object causes the planet to gain or lose energy. -Left undisturbed, planets will forever keep the same orbits in their galaxies. -Gravitational Encounter: 2 objects exchange energy if they pass near enough that each can feel the effects of the other's gravity. ex) When a comet passes very close to a planet, the comet's orbit will change dramatically due to the gravity exerted from the planet. Escape Velocity: The minimum amount of energy required to escape Earth's gravity for a spacecraft that starts on the surface.

Acceleration of Gravity

-The acceleration of a falling object (abbreviated g) -As an object falls, its speed is increased 10m/s ex) When a rock is dropped off the top of a building, it goes 0m/s when its dropped, 10m/s after 1 second, 20 m/s after 2 seconds, etc. THEREFOR, we say that the Acceleration of Gravity is 10 meters per second per second, or 10 m/s^2

Bound vs. Unbound orbit

-Unbound: Paths that bring an object close to another one just once (parabolas or hyperbolas) -Bound: An object orbits around the same object over and over again (make ellipses)

Calculate the angular area of the HST's field of view in square degrees.

0.0036 square degrees

Newton's 3 Laws of Motion, with examples:

1) An object moves at constant velocity if there is no net force acting upon it -ex) A car parked on a flat street won't suddenly start moving. When the car is driven, and then the foot is taken off the pedal, it will go at the same speed until air and friction slows it down. 2) Force = Mass x Acceleration Force = Rate of Change in momentum -ex) You can throw a baseball further than a shot put because your arm gets more acceleration with a baseball. 3) For any force, there is always an equal and opposite reaction force. -ex) Force is what keeps us on the ground of earth, but earth itself is also pushing us at an equal force towards space. Since they're equal, we stay on the ground.

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

4 times

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 times

Suppose astronomers built a 80-meter telescope. How much greater would its light-collecting area be than that of the 10-meter Keck telescope?

64

Which of the following statements best describes the difference between a refracting telescope and a reflecting telescope?

A refracting telescope uses a transparent glass lens to focus light while a reflecting telescope uses a mirror to focus light.

4. What is a spectrum and how do we see one?

A spectrum, more specifically an electromagnetic spectrum, is a scale of wavelengths of different types of light-even those we cannot see. The Visible Light section (which is the only part we can see) is only a tiny, tiny portion of the whole spectrum.

16. Explain the atomic structure of the atom. Tell how this creates the distinctive patterns of emission and absorption spectra.

An atom consists of protons, neutrons, and electrons. Protons and Neutrons are found in the nucleus in the center of the atom, while electrons surround the nucleus. The electron collisions sometimes transfer just the right amount of energy to change energy levels causing the lost energy to emit a photon of light. This happens in moderately warm gas clouds. When atoms absorb photons with the right amount of energy needed to raise an electron from a lower to a higher energy level, that create the distinctive patterns of the absorption spectra. Basically, light produces a continuous rainbow, but hydrogen atoms get in the way and absorb light at specific wavelengths.

The _______ ________ of the Hubble Space Telescope is better for shorter (bluer) wavelengths of light than for longer (redder) wavelengths of light

Angular Resolution

10. Briefly describe the structure of an atom. How big is an atom? How big is the nucleus in comparison to the entire atom?

Atoms come in different types, and each type corresponds to a different chemical element, protons neutrons and electrons make it up, and P and N make up the nucleus; The nucleus is almost 100,000 times smaller than the atom.. BUT it contains almost all of its mass (since P & N are 2000x more massive than electrons).

Velocity

Both speed and direction

How does your eye focus light? How is a glass lens similar? What do we mean by focal plane of a lens?

By bending light to a focus point on the retina; by bending parallel rays of light to a focus point of the lens; focal plane is where the image appears in focus.

How does a camera record light? How are images affected by exposure time? What are pixels?

Camera has a small opening for light to enter, like the pupil of the eye, lens bends the light, bringing it to a focus on a detector that makes a permanent record of the image. Longer exposure= more detail. Pixels- electronic chips that are physically divided into grids of picture elements, used in modern detectors.

17. Describe the conditions that would cause us to see each of the three basic types of spectra. What do we see in the Sun's spectrum shown on the opening page of this chapter?

Continous: light bulb produces light of all colors Ex. Incandescent light bulb Emission Line: gas cloud emits light at specific colors depeding on its composition and temperature Absorption Line: Light from a hot source passes through a cooler gas cloud (which absorbs certain wavelengths [colors])

12. What is electrical charge? Will an electron and a proton attract or repel one another? Will two electrons attract or repel one another? Explain.

Electrical charge is a fundamental property that describes how strongly an object will interact in electromagnetic fields. Protons and electrons would attract, but electrons and electrons would not attract.

14. What do we mean when we say that energy levels are quantized in atoms? Under what circumstances can energy level transitions occur?

Electrons have quantized energy levels in all atoms, not just in hydrogen. Quantized means that they are sudden changes with no in-between level. Energy level transitions can occur only when an electron gains or loses the exact amount of energy that separates two energy levels.

5. Give an example from everyday life of each of the four major types of interaction between matter and light.

Emission: light bulb emits visible light Absorption: hand absorbs light if its near a light bulb Transmission: glass and air transmit light Reflection: light can bounce off matter and go in different directions

I have a reflecting telescope in which the secondary mirror is bigger than the primary mirror.

False

I wanted to see faint details in the Andromeda Galaxy, so I photographed it with a very short exposure time.

False

Thanks to adaptive optics, telescopes on the ground can now make ultraviolet images of the cosmos.

False

33. Galaxies that show redshifts must be red in color.

False. For distant galaxies, the light spectrum is wrong. The frequency lines of the spectrum are all too low. One possible explanation of the incorrect spectrum is that those stars and galaxies are moving away from us, and that the spectrum is shifted toward the red end of the color spectrumm because of the Doppler effect.

28. If you had X-ray vision, you could read this entire book without turning any pages.

False. If you were using x-ray vision, you would not be able to resolve the letters on individual pages.

29. Two isotopes of the element rubidium differ in their number of protons.

False. Isotopes of the same element must differ in the number of neutrons, not protons. If the isotopes differed in the number of protons, they would be completely different elements.

30. If you could view a spectrum of light reflecting off a blue sweatshirt, you'd find the entire rainbow of color.

False. You would see only blue coloring. Blue objects absorb all of the colors of the rainbow other than blue.

What is free-fall, and why does it make you feel weightless? Briefly explain why astronauts are weightless in the space station.

Free-fall: falling without any resistance to slow you down. The floor drops away at the same rate that you fall, allowing you to float freely above it, causing you to be weightless. Astronauts are constantly weightless because they're in a constant rate of free-fall. Everything orbiting around Earth is constantly "falling around" (orbiting) earth -EX) the running and jumping example from the book

Speed

How far something will go in a certain amount of time

18. How can we use emission or absorption lines to determine the chemical composition of a distant object?

Hydrogen emits and absorbs light at specific wavelengths, therefore if youre looking at a distant cloud that produces a certain spectrum (w/ certain absorption lines), you can know its made of hydrogen. Each chemical and its ions leave different "fingerprints."

What do we mean when we speak of images made from invisible light, such as x ray or infared images? What do the colors in these images mean?

Images made with invisible light cannot have any natural color because color is a property only of visible light. We can use color-coding to interpret them. Sometimes color can respond to different energy levels or according to light intensity or to physical properties of objects in the images.

What are the three basic categories of astronomical observation, and how is each conducted?

Imaging: yields photographs of astronomical objects. Spectroscopy: astronomers obtain and study spectra. Time monitoring: tracks how a distant object's brightness changes with time.

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

What is interferometry can how can it improve astronomical observations?

Interferometry: linking of two or more individual telescopes to achieve angular resolution of a much larger telescope; works by taking advantage of wave-like properties of light that cause interference.

What is the purpose of interferometry?

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

Which of the following best describes what we mean by the focal plane of a telescope?

It is the place where, if we mounted film or an electronic detector, we could get a clear (not blurry) image of an object viewed through the telescope.

What is the purpose of adaptive optics?

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

22. Describe each of the key features of the Martian spectrum and explain what it tells us about the object.

Key features of the martian spectrum include the dashed line of the continuous spectrum (caused by the Sun's reflected light), the high intensity of the scattered red light (tells us the chemical composition of Mars-its blue), the peak in the thermal radiation is in the infrared (tells us its much cooler than the Sun), emission lines in the UV (tells us Mars' atmosphere contains hot gas at high altitudes), absorption lines (tells us about CO2 in the atmosphere), and the Doppler Effect (towards red means Mars is moving away and towards Blue means towards us)

8. What is a photon? In what way is a photon like a particle? In what way is it like a wave?

Light behaves as both a wave and a particle, light comes in individual pieces called photons. Particle: photons of light can be counted individually. Wave: each photon is characterized by a wavelength and frequency

What do astronomers mean by light pollution?

Light pollution is light from human sources that makes it difficult to see the stars at night.

7. What do we mean when we say that light is an electromagnetic wave?

Light waves are traveling vibrations of both electric and magnetic fields

What are the 2 key properties of a telescope, and why is each important?

Light-collecting area: determines how much light it gathers. angular resolution: determines how much detail we can see in its images.

Momentum

Mass x Velocity

What do we mean by "mass-energy"? Define e=mc squared.

Mass-Energy: Mass itself is a form of energy -e=mc^2 tells us that a small amount of mass contains a huge amount of energy. -It also tells us that energy can be converted into mass ex) The Big Bang Theory turned energy into mass, creating everything in the universe including us.

What do we mean when we say that momentum can be changed only by a net force?

Momentum is not necessarily changed by force, but it is changed when its net force (overall force) is not zero.

Suppose that two stars are separated in the sky by 0.1 arcsecond. If you look at them with a telescope that has an angular resolution of 0.5 arcsecond, what will you see?

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

Describe how deeply each portion of the electromagnetic spectrum penetrates Earth's atmosphere. Based on your answers, why are space telescopes so important to our understanding of the universe?

Only radio waves, visible light, the very longest wavelengths of ultraviolet light, and small parts of the infared spectrum can be observed from the ground. Space telescopes are important because they allow us to observe the rest of the electromagnetic spectrum.

How do telescopes of invisible wavelengths differ from those for visible light? Answer for each major wavelength band and give examples of important observatories in those bands.

Radio telescope: angular resolution important bc they aren't used to make images of the satelites in space

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

Radio waves and Visible light

The large research observatories on Mauna Kea use giant ________ __________.

Reflecting Telescopes

How do reflecting telescopes differ from refracting telescopes? Which type is more commonly used by professional astronomers, and why?

Refracting telescope: operates like an eye, using transparent glass lenses to collect and focus light. Reflecting telescope: uses a precisely curved primary mirror to gather light. Reflecting telescopes are more commonly used because only the reflecting surface of a mirror must be precisely shaped, quality of the underlying glass is not a factor, and since mirror is located at the bottom its weight isn't a problem.

List at least three ways in which Earth's atmosphere can hinder astronomical observations. What problem can adaptive optics help with?

Scattering of human-made light, blurring of images by atmospheric motion, and the fact that most forms of light cannot reach the ground at all. Adaptive optics help eliminate blurring.

3. Think of three very different ways I could create the red light for the demonstration above.

Shine a red lightbulb, a white lightbulb with a red film piece over it, or put a red bottle top on the end of a flashlight. Basically this would work because you absorb all of the other colors except red. OR. Produce an emission line of only red light w/ for example, a laser. Purpose of this is because red light does not affect your night-vision.

What do we mean by spectral resolution? Why is higher spectral resolution more difficult to achieve?

Spectral resolution is the amount of detail we can see. The higher the spectral resolution, the more detail. BUT, b/c the spectral resolution depends on how widely the spectrograph spreads out the light, if the light is spread out more, you need more total light in order for it to be recorded successfully. So making a spectrum of an object requires a longer exposure time than making an image, and higher resolution spectra require longer exposures than low-resolution spectra.

_____________ separate the various colors of light, allowing astronomers to determine stellar composition and may other stellar properties.

Spectrographs

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.

Temperature vs. Thermal Energy

Temperature: measures the AVERAGE kinetic energy of the particles. Thermal Energy: measures the TOTAL kinetic energy of all the randomly moving particles in a substance -SIMILAR because thermal energy depends on temperature -DIFFERNT because TEMPERATURE measures the avg. speed of movement, and THERMAL measures the mass of a substance

23. Describe the Doppler effect for light and what we can learn from it. What does it mean to say that radio waves are blue shifted? Why does the Doppler effect widen the spectral lines of rotating objects?

The Doppler Effect is when the wavelengths of spectral lines are slightly shifted depending on the velocity of the light and whether it is moving towards or away from us as it orbits the Sun. Blue-shifted (closer together) radio waves means the object is moving towards us. The Doppler effect widens the spectral lines of rotating objects because the wavelengths changes from blue or red. Blue-shifted, red-shifted, and non-shifted photons mix together to get how its rotating.

Acceleration

The change in velocity in any way, whether in speed, direction, or both.

Force

The only way to change an object's momentum is to apply force to it

1. What is this? What are the dark lines?

The picture is of an Absorption Line Spectrum, which is when a cloud of gas lies between a hot light source and us. Specifically, this picture is showing the Sun's visible light spectrum (but in great detail). The dark lines are called absorption lines, which are where the cloud absorbs specific wavelengths, or colors, of light leaving a spot with a drop of wavelength intensity. The "clouds" in this picture are the Sun's visible surface called the "photoshere."

19. How do the properties of light allow us to determine the physical properties of stars?

The properties of light allow us to determine the physical properties of stars mainly by temperatures. The first law of thermal radiation states that each square meter of a hotter object's surface emits more light at all wavelengths. The second law states that hotter objects emit photons with a higher average energy. Use the absorption spectrum to find chemical composition. Blue stars are hot and red stars are cool.

15. How do we convert a continuous spectrum shown as a band of light (like a rainbow) into a graph of the spectrum?

Through spectroscopy. And then changing them from showing only visible light to showing the amount of radiation, or intensity, at each wavelength.

If you lived on the moon, you'd never see stars sparkle.

True

True or false: The image was blurry because the detector was not placed at the focal plane.

True

31. A "white hot" object is hotter than a "red hot" object.

True. An object must emit a red color from heat before it can emit a white color, because white is all of the colors combined.

25. The walls of my room are transparent to radio waves.

True. The fact that the walls are transparent to radio waves means that they would allow the radio waves to enter into the room, which is an accurate statement.

34. If a distant galaxy has a substantial redshift (as viewed from our galaxy), then anyone living in that galaxy would see a substantial redshift in a spectrum of the Milky Way Galaxy.

True. The increasing distance between the two galaxies will red shift light traveling between them in either direction.

27. If you could see infrared light, you would see a glow from the backs of your eyelids when you closed your eyes.

True. The infrared light would be able to penetrate through my eyelids because they are not completely opaque to wavelengths.

32. If the Sun's surface became much hotter (while the Sun's size remained the same), the Sun would emit more ultraviolet light but less visible light than it currently emits.

True. When heat increases, so does the frequency and energy of the wavelengths. Because of this, some visible light would be converted to ultraviolet light.

26. Because of their higher frequencies, X rays must travel through space faster than radio waves.

True. X-rays have both a higher energy and frequency, and therefore will travel through space faster than radio waves.

Which of the following effects is caused by atmospheric turbulence?

Twinkling of stars

13. Describe the phase changes of water as you heat it starting from its solid phase, ice. What happens at very high temperatures? What is a plasma?

Water will be in a solid from as ice and as it heats up it becomes a liquid form known as water. When it obtains enough energy it will become its gaseous form through a process called evaporation. A plasma is a type of hot gas in which atoms have ionized. Because a plasma contains many charged particles, its interactions with light are different from those of a gas consisting of neutral atoms, which is one reason that plasma is sometimes referred to as "the fourth phase of matter". ex's. solid=desk, liquid=beer, gas=nitrogen, plasma=fluorescent lights

6. Define wavelength, frequency, and speed for a wave.

Wavelength: distance from one peak to the next Frequency: number of peaks passing by any point each second Speed for a wave: how fast the peaks travel across the pond

2. On a very strange whim I have painted my windowless room blue [450nm] with a white ceiling and a black floor. I turn on a red [650nm] light. What do I see? What if I had a detector sensitive to the infrared?

You would see a red ceiling, a black floor still, and your walls would still appear black because a blue wall reflects only blue light and absorbs all others, (but since there's no blue photons, they cant reflect) which means it If you had a detector, the whole thing would be red.

Interferometry uses two or more telescopes to achieve

angular resolution equivalent to a larger telescope

What is the diffraction limit and how does it depend on a telescope's size and wavelength of light being observed?

diffraction limit: the angular resolution that a telescope could achieve if it were limited only by the interference of light. Larger telescope= smaller diffraction limit. Diffraction limit is larger for light with longer wave length.

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

four times

h

g

The Chandra X-Ray observatory focuses X rays with _________ _________ mirrors.

grazing incidence

g

h

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

Where should you put a telescope designed for ultraviolet observations?

in Earth orbit

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.

What does it mean if you see the color red in an X-ray image from the Chandra X-ray observatory?

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

The Hubble Space Telescope obtains higher-resolution images than ground-based telescopes because...

it is larger

A 10-meter telescope has a larger __________-_________ _____ than a 4-meter telescope.

light-collecting area

Which of the following wavelength regions can be studied with telescopes on the ground?

radio, visible, and very limited portions of the infrared and ultraviolet regions

Galileo's telescope designs using lenses were examples of _________ ________.

refracting telescope

When your eye forms an image, the _____ plays a role analogous to the detector in a camera.

retina

What does angular resolution measure?

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