AST Exam 2 Review (Ch 5, 6, 14, 15
What do we need to measure in order to determine a star's luminosity?
apparent brightness and distance
What are the three basic types of spectra?
emission, continuous, absorption
Which of these groups of particles has the greatest mass? A.) a helium nucleus with two protons and two neutrons B.) four electrons C.) four individual protons
four individual protons
How much greater is the light-collecting area of a 6-meter telescope than a 3-meter telescope?
four times
If the star Alpha Centauri were moved to a distance 10 times farther than it is now, its parallax angle would...
get smaller.
At the center of the Sun, fusion converts hydrogen into...
helium, energy, and neutrinos.
Main-Sequence Star Summary
high mass: high luminosity, short lived, large radius, blue low mass: low luminosity, long lived, small radius, red
Compared to red light, blue light has higher frequency and...
higher energy and shorter wavelength than red light.
proton-proton chain
how hydrogen fuses into helium in Sun.
Diffraction limit
limit on angular resolution
A spectral line that appears at a wavelength of 321 nmnm in the laboratory appears at a wavelength of 328 nmnm in the spectrum of a distant object. We say that the object's spectrum is:
redshifted.
Redshift
shift of light to a longer wavelength as it moves away
Some nitrogen atoms have seven neutrons and some have eight neutrons. What are these two forms of nitrogen?
They are isotopes of each other.
Which technology can allow a single ground-based telescope to achieve images as sharp as those from the Hubble Space Telescope?
adaptive optics
Chemical Fingerprints
(1) Each type of atom has a unique spectral fingerprint. (2) Observing the fingerprints in a spectrum tells us which kinds of atoms are present.
Why does the Sun shine?
- Chemical and gravitational energy sources could not explain how the Sun could sustain its luminosity for more than about 25 million years. - The Sun shines because gravitational equilibrium keeps its core hot and dense enough to release energy through nuclear fusion.
What are the two most important properties of a telescope?
- Collecting area determines how much light a telescope can gather. - Angular resolution is the minimum angular separation a telescope can distinguish.
Why do we put telescopes into space?
- Forms of light other than radio and visible do not pass through Earth's atmosphere. - Also, much sharper images are possible because there is no turbulence.
How does light tell us the temperatures of planets and stars?
- Nearly all large or dense objects emit a continuous spectrum that depends on temperature. - The spectrum of that thermal radiation tells us the object's temperature.
What are the two basic designs of telescopes?
- Refracting telescopes focus light with lenses. - Reflecting telescopes focus light with mirrors. - The vast majority of professional telescopes are reflectors.
What are giants, supergiants, and white dwarfs?
-Giants and supergiant's are stars that have exhausted their central core supplies of hydrogen for fusion and are undergoing other forms of fusion at a prodigious rate as they near the ends of their lives. White dwarfs are the exposed cores of stars that have already died, meaning they have no further means of generating energy through fusion.
How do we measure stellar luminosities?
-If we measure a star's apparent brightness and distance, we can compute its luminosity with the inverse square law for light. -Parallax tells us distances to the nearest stars.
What is the significance of the main sequence?
-Stars on the main sequence are all fusing hydrogen into helium in their cores, and a star's position along the main sequence depends on its mass. High-mass stars are at the upper left end of the main sequence, and the masses of stars become smaller as we move toward the lower right end. Lifetimes vary in the opposite way, because high-mass stars live shorter lives
Wavelength and Frequency
-inversely related -the shorter the wavelength, the higher the frequency wavelength × frequency = speed of light = constant
We learn about the inside of the Sun by
-making mathematical models -observing solar vibrations -observing solar neutrinos
Gamma-Ray Telescopes
-need to be in SPACE -Focusing gamma rays is extremely difficult
Emission Line Spectrum
A thin or low-density cloud of gas emits light only at specific wavelengths that depend on its composition and temperature, producing a spectrum with bright emission lines.
Waves
A wave is a pattern of motion that can carry energy without carrying matter along with it.
Convection Zone:
Energy transported upward by rising hot gas
How do we know what is happening inside the Sun?
Mathematical models agree with observations of solar vibrations and solar neutrinos.
Off the Main Sequence
-stellar properties depend on both mass and age: those that have finished fusing H to He in their cores are no longer on the main sequence -all stars become larger and redder after exhausting their core hydrogen: giants and supergiants -most stars end up small and white after fusion has ceased: white dwarfs
Properties of Thermal Radiation
1. Hotter objects emit more light at all frequencies per unit area. 2. Hotter objects emit photons with a higher average energy. Hottest stars: 50,000 K • Coolest stars: 3000 K • (Sun's surface is 5800 K.)
Sun's life expectancy:
10 billion years (until core hydrogen, 10% of total, is used up).
Suppose astronomers built a 50-meter telescope. How much greater would its light-collecting area be than that of the 10-meter Keck telescope?
25
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
blueshift
A Doppler shift in which spectral features are shifted to shorter wavelengths, observed when an object is moving toward the observer.
Absorption Line Spectrum
A cloud of gas between us and a light bulb can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum.
Sunspots
A dark area of gas on the sun's surface that is cooler than surrounding gases.
Choose the correct definition of a molecule.
A molecule is a group of two or more atoms bound together.
Radiation Zone:
A region of very tightly packed gas in the sun's interior where energy is transferred mainly in the form of light. - Energy transported upward by photons
How do we measure the age of a star cluster?
A star cluster's age roughly equals the life expectancy of its most massive stars still on the main sequence.
How do we measure stellar temperatures?
A star's color and spectral type both reflect its temperature.
The diffraction limit is a limit on:
A telescope's angular resolution.
Luminosity:
Amount of power a star radiates (energy per second = watts) Actual brightness of a star
What is a Hertzsprung-Russell diagram?
An H-R diagram plots stellar luminosity of stars versus surface temperature (or color or spectral type).
What is a Hertzsprung-Russell diagram?
An H-R diagram plots the luminosity and temperature of stars • Stars with lower T and higher L than main-sequence stars must have larger radii. These stars are called giants and supergiants. • Stars with higher T and lower L than main-sequence stars must have smaller radii. These stars are called white dwarfs.
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.
solar flares
An eruption of gas from the sun's surface that occurs when the loops in sunspot regions suddenly connect
How do we measure stellar luminosities?
Brightness of a star depends on both distance and luminosity.
How does the energy from fusion get out of the Sun?
Can take ~100,000 years for a photon formed at the core to escape Convection (rising hot gas) takes energy to surface. • Randomly bouncing photons carry energy through the radiation zone. • Rising of hot plasma carries energy through the convection zone to photosphere.
Radio Telescopes
Devices used to detect radio waves from objects in space
How much larger is the diffraction limit at 1000 nm compared to 500 nm for a telescope of the same diameter?
Diffraction Limit= 2.5E5" x wavelength/Diameter (Diff. Limit at 1000 nm) / (Diff. Limit at 500 nm) = 1000/500 = 2 It is 2 times larger
Choose the correct definition of electrical charge.
Electrical charge is a measure of how strongly something will interact with electromagnetic fields.
Under what circumstances can energy level transitions occur?
Electrons can make a transition from one level to another by taking in or emitting a specific amount of energy. If too much or too little energy is offered, the electron cannot make the transition.
How do light and matter interact?
Emission, absorption, transmission (transparent objects transmit light) Opaque objects block (absorb) light, reflection or scattering
What is the Sun's structure?
From inside out, the layers are: Core, Radiation Zone, Convection Zone, Photosphere, Chromosphere, Corona
Stellar Luminosity Classes
I - supergiant II - bright giant III - giant IV - subgiant V - main sequence
How does a natural "solar thermostat" keeps the core fusion rate steady in the Sun?
If the Sun's core were a bit hotter, the fusion rate would increase. This would produce more energy, which would cause the core to expand slightly and cool. The cooling would cause the fusion rate to slow back down until the Sun was back to the original size and temperature and fusion occurred at the original rate.
What do astronomers do with telescopes?
Imaging, spectroscopy, timing monitoring
Infrared and Ultraviolet Telescopes
Infrared and ultraviolet light telescopes operate like visible-light telescopes but need to be above atmosphere to see all wavelengths.
Interactions of Light with Matter
Interactions between light and matter determine the appearance of everything around us
I measure a line in the lab at 500.7 nm. The same line in a star has wavelength 502.8 nm. What can I say about this star?
It is moving away from me.
Why is a sunflower yellow? A) It emits yellow light. B) It absorbs yellow light. C) It reflects yellow light.
It reflects yellow light.
How would the apparent brightness of Alpha Centauri change if it were three times farther away?
It would be only 1/9 as bright.
How does the collecting area of a 10-meter telescope compare with that of a 2-meter telescope?
Its 25 times greater
What is light?
Light can act either like a wave or like a particle. Particles of light are called photons.
How do mathematical models help us learn about conditions inside the Sun?
Mathematical models use the observed composition and mass of the Sun along with the laws of physics to derive equations that describe the gravitational equilibrium, solar thermostat, and rate at which energy moves from the core to the photosphere.
Thermal Radiation
Nearly all large or dense objects emit thermal radiation, including stars, planets, you. - An object's thermal radiation spectrum depends on only one property: its temperature.
How do we measure stellar masses?
Newton's version of Kepler's third law tells us the total mass of a binary system, if we can measure the orbital period (p) and average orbital separation of the system (a).
Suppose that two stars are separated in the sky by 0.1 arcsecond. 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.
What are the two types of star clusters?
Open clusters are loosely packed and contain up to a few thousand stars. Globular clusters are densely packed and contain hundreds of thousands of stars.
What is the structure of matter?
Ordinary matter is made of atoms, which are made of protons, neutrons, and electrons. Atoms of different chemical elements have different numbers of protons. Isotopes of a particular chemical element all have the same number of protons but different numbers of neutrons. Molecules are made from two or more atoms.
Suppose you could travel to Jupiter and observe changes in positions of nearby stars during one orbit of Jupiter around the Sun. How would your ability to measure the distances to stars be different from the vantage point of Jupiter.
Parallax distances would be easier to measure from Jupiter's orbit—for the same accuracy, one could measure distances about five times farther than we can from Earth.
Adaptive optics
Rapid changes in mirror shape compensate for atmospheric turbulence.
What are the two basic designs of telescopes?
Refracting telescope: focuses light with lenses (Refracting telescopes need to be very long, with large, heavy lenses) Reflecting telescope: focuses light with mirrors (Reflecting telescopes can have much greater diameters.)
What is refraction?
Refraction is the bending of light when it passes from one substance into another. Your eye uses refraction to focus light.
Fusion
Small nuclei stick together to make a bigger one. (Example: the Sun, stars)
Why do the properties of some stars vary?
Some stars fail to achieve balance between power generated in the core and power radiated from the surface
angular resolution
Telescopes that are larger are capable of taking images with greater detail.
light-collecting area
Telescopes with a larger collecting area can gather a greater amount of light in a shorter time.
How does light tell us the speed of a distant object?
The Doppler effect tells us how fast an object is moving toward or away from us.
Alpha Centauri and the Sun have about the same luminosity. Which one appears brighter?
The Sun
How does nuclear fusion occur in the Sun?
The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus. - High temperatures enable nuclear fusion to happen in the core.
Measuring the Shift
The amount of blueshift or redshift tells us an object's speed toward or away from us.
How does Earth's atmosphere affect ground- based observations?
The best ground-based sites for astronomical observing are: • calm (not too windy) • high (less atmosphere to see through) • dark (far from city lights) • dry (few cloudy nights) The best observing sites are atop remote mountains.
Core:
The central part of the earth below the mantle - Energy generated by nuclear fusion
Doppler effect
The change in frequency of a wave as its source moves in relation to an observer
Chromosphere:
The middle layer of the sun's atmosphere
Choose the correct statement about an atomic nucleus, compared to an atom as a whole.
The nucleus is very tiny but has most of the mass.
How does solar activity vary with time?
The number of sunspots rises and falls in an 11-year cycle
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.
Why do sunspots appear darker than their surroundings?
They are cooler than their surroundings.
Suppose you could travel to Jupiter and observe changes in positions of nearby stars during one orbit of Jupiter around the Sun. How would those changes be different from what we measure from Earth?
The parallax of stars, as viewed from the orbit of Jupiter, would be about five times larger, since Jupiter's orbit around the Sun is about five times larger than that of Earth.
Why is a rose red?
The rose reflects red light.
Fission
The splitting of an atomic nucleus to release energy.
What causes solar activity?
The stretching and twisting of magnetic field lines near the Sun's surface causes solar activity. Bursts of charged particles from the Sun can disrupt communications, satellites, and electrical power generation.
News of a solar flare caused concern among businesses involved in communication and electrical power generation. Choose the correct explanation of whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false).
This statement is sensible. Solar flares can cause havoc with satellites, communication networks, and power grids because of the energetic charged particles released.
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. Choose the correct explanation why the statement makes sense (or is clearly true) or does not make sense (or is clearly false).
This statement makes sense. The redshift means that we see the galaxy moving away from us, so observers in that galaxy must also see us moving away from them—which means they see us redshifted as well.
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.
How can we be confident that the models are on the right track?
We can check the models by comparing their predictions for radius, surface temperature, and luminosity, as well as other observable parameters generated by studying helioseismology. The models do indeed make predictions that allow us to explain these observations; we are on the right track.
Choose the correct explanation of an electron and a proton or two electrons attracting or repelling one another.
We define a proton as having +1 unit of charge and an electron as having -1 unit when talking about atoms and particles. Two particles with charges of different sign will attract each other, so protons and electrons will attract. Particles with charges of the same sign will repel each other, so two electrons will repel each other.
What do we mean when we say that energy levels are quantized in atoms?
We mean that the electrons can have only discrete values of electrical potential energy in atoms.
Choose the correct description of what do we mean when we say that light is an electromagnetic wave and the relationship among wavelength, frequency, and speed for light waves.
We say that light is an electromagnetic wave because light is a oscillation of electric and magnetic fields. frequency=speed of light/wavelength
Choose the correct description, of how would we be able to tell, if fusion reactions in the Sun were to suddenly cease.
We would be able to tell that fusion reactions had ceased because we would no longer detect neutrinos from the Sun. Neutrinos, a by-product of nuclear fusion, exit the Sun immediately.
Which of these stars has the greatest surface temperature? A.) a 30MSun main-sequence star B.) a supergiant A star C.) a Cepheid variable star
a 30MSun main-sequence star
Which of these stars has the coolest surface temperature? A.) an A star B.) an F star C.) a K star
a K star
Radio waves are
a form of light
Which of these stars is the most massive? A) a main-sequence A star B.) a main-sequence G star C.) a main-sequence M star
a main-sequence A star
Eclipsing Binary
a star system in which one star periodically blocks the light from another
Which of these stars has the largest radius? A.) a supergiant A star B.) a giant K star C.) a supergiant M star
a supergiant M star
If you heat a rock until it glows, its spectrum will be:
a thermal radiation spectrum
The Hubble Space Telescope obtains higher-resolution images than most ground-based telescopes because it is:
above Earth's atmosphere.
Coronal mass ejections
bursts of charged particles from the Sun's corona that travel outward into space
The set of spectral lines that we see in a star's spectrum depends on the star's:
chemical composition
Compared to the Sun, a star whose spectrum peaks in the infrared is:
cooler
Scientists estimate the central temperature of the Sun using
mathematical models of the Sun.
Transmission through Earth's Atmosphere...
only radio and visible light pass easily through earth's atmosphere, we need telescopes in space to observe other forms.
Solar energy leaves the core of the Sun in the form of...
photons.
Which of these layers of the Sun is coolest?
photosphere
Main-sequence stars
stars that are in the main part of their lifecyle • Main-sequence stars are fusing hydrogen into helium in their cores like the Sun. • Luminous main- sequence stars are hot (blue). • Less luminous ones are cooler (yellow or red). • Mass measurements of main-sequence stars show that the hot, blue stars are much more massive than the cool, red ones. • The mass of a normal, hydrogen- burning star determines its luminosity and spectral type. • Core pressure and temperature of a higher- mass star need to be larger in order to balance gravity. • Higher core temperature boosts fusion rate, leading to larger luminosity.
Pulsating Variable Stars
stars which go through peridos of swelling and brightening, then shrinking and dimming. the absolute magnitude changes.
Angular resolution
telescopes that are larger are capable of taking images with greater detail
parallax
the apparent change in position of an object when seen from different places Parallax tells us distances to the nearest stars.
Parallax
the apparent shift in position of a nearby object against a background of more distant objects.
Apparent brightness:
the brightness of a star as it appears from Earth
Solar wind:
the continuous flow of charged particles from the sun that permeates the solar system.
angular resolution
the minimum angular separation that the telescope can distinguish
Corona:
the outermost layer of the sun's atmosphere
What two pieces of information would you need in order to measure the masses of stars in an eclipsing binary system?
the time between eclipses and the average distance between the stars
Continuous Spectrum
the uninterrupted broad band of all colors (wavelengths) emitted by incandescent solids
Photosphere:
the visible surface of the sun
X-Ray Telescopes
used to look at the sun; uses interaction of x-rays and matter, need to be above atmosphere
Cepheid Variable Stars
variable stars with pulsation periods of 1 to 60 days whose period of variation is related to their luminosity • Most pulsating variable stars inhabit an instability strip on the H-R diagram. • The most luminous ones are known as Cepheid variables. • Their periods of brightness change are indicative of their luminosity • Important "cosmic lighthouses"
What is the "peak" color for an object half as hot as the sun?
wavelength x temperature = 3000 micron-K (wl in microns, T in K) Sun is yellow, which corresponds to ~500nm If temperature is half, than wavelength has to double ~1000 nm (really blue)
Your body temperature (provided you are not a vampire) is 98 F ( 37 celsius ). What is your peak "color"?
wavelength x temperature = 3000 micron-K (wl in microns, T in K) wavelength = 3000/ Temperature Temperature = 37 C = 37+273 = 310 K wavelength = 3000/ 310 = 9.67 microns
Spectroscopic Binary
we determine the orbit by measuring Doppler shifts
Wavelength, Frequency, and Energy
λ × f = c c = 3.00 × 108 m/s = speed of light
How do we measure the age of a star cluster?
• Massive blue stars die first, followed by white, yellow, orange, and red stars. • The main- sequence turnoff point of a cluster tells us its age. © 2017 Pearson Education, Inc. • Detailed modeling of the oldest globular clusters reveals that they are about 13 billion years old.
How do we measure stellar masses?
• We can directly observe the orbital motions of these stars. • If we know distance from parallax, can *directly measure* separation. Can observe orbital period. Can determine center of mass
Visual Binary
• We can directly observe the orbital motions of these stars. • If we know distance from parallax, can *directly measure* separation. Can observe orbital period. Can determine center of mass Can be distinguished using a telescope The orbit of a binary star system depends on strength of gravity.
