astronomy exam 1
The red color we see on a lot of photographs of nebulae comes from which element?
hydrogen
steps of pp chain
1h 1h = 2h neutrino and positron 2h 1h= 3he gamma ray 3he 3he= 4he 1h 1h
eclipsing binary
a pair of gravitationally bound stars that can only be indentified as a binary by using careful study of the brightness
double star
a pair of stars that appear close to eachother in the sky but may or may not be a bound system
spectroscopic binary
a pari of gravitationally bound stars that can only be identified as a binary by using careful study of the spectrum
How many protons are in a deuterium atom?
1
A major breakthrough in measuring astronomical distances came with a better understanding of a group of variable stars called ___________ whose brightness changes in a regular and repeating way. The astronomer who in 1908 noticed a relationship between the period of variations and the luminosity of these stars was ________________. Since it's easy to measure the period of variations, the relationship turned out to be very valuable. From the period, astronomers can use the relationship to get the luminosity. Since we know how light gets dimmer with increasing distance, comparing the star's luminosity with its ___________ allows them to calculate the distance. Today, astronomers can use these variable stars to measure the distance to other ___________, great "islands of stars" millions of light-years away.
1. cepheids 2. Henrietta Leavitt 3. apparent brightness 4. galaxies
Astronomers estimate that some 15% of the mass of the stars in our galaxy is present as gas and dust between the stars - together this material is called the ________________. When interstellar material surrounds one or more hot stars, the simplest atoms of gas can become ionized, forming ___________. When the simplest atoms of gas are cold, they are hard to detect using visible light. However, they do give off __________ at a wavelength of 21 cm. One of the surprise discoveries of the 20th century was that, in denser clouds of interstellar gas and dust, more complex _____________, like acetic acid or formaldehyde, can be formed. In addition to gas, the clouds of interstellar material also contain solid particles of dust, which can be observed using _________.
1. interstellar medium 2. HII regions 3. radio waves 4. molecules 5. infrared waves
The value of the H-R Diagram is that it helps astronomers understand the life history of stars. Careful surveys reveal that 90% of all stars are ______________ on the diagram. Deep inside, these stars are _____________ and will be doing so for 90% of their lives. The more massive the star, the ________ its life in this stage. About 10% of the stars are ______________ in the diagram. These stars are dying stars, and they are very __________. The stars at the upper right of the diagram, on the other hand, are _______________.
1. on the main sequence 2. fusing hydrogen into helium 3. shorter 4. in the white dwarf region 5. dense 6. very large and less dense than the sun
Generally, when we observe the Sun (with the right filters so we don't burn our eyes out,) we see only the "surface" of the Sun, which astronomers call the _____________. Seeing deeper into the Sun is much more difficult, but astronomers have found two ways to do so. The technique of measuring small "oscillating regions" (moving toward us and then away from us) is called ______________. The waves from the pulsations of the Sun take only ______ to make it from center to the surface. Another technique of looking deep into the Sun involves catching the elusive particles called ____________ here on Earth. These particles from the Sun were first detected in significant numbers in experiments that changed __________ atoms into radioactive argon. These particles are created during nuclear fusion reactions in the Sun, in a sequence of reactions that scientists call ______________.
1. photosphere 2. helioseismology 3. a little over an hour 4. neutrinos 5. chlorine 6. PP chain
The Sun is so hot that its material is in the form of a _________. Gravity is always producing a force that tends to make the Sun collapse toward its center. To balance this force, the energy produced by nuclear fusion produces an outward _________, allowing the Sun to be in a condition of ___________. Inside the Sun, energy is transported via __________, where hot material rises and cooler material falls downward. Energy is also transported outward via ____________, but photons take between 100,000 and 1,000,000 years to reach the Sun's surface. On the other hand, ________ produced by nuclear fusion at the center reach the surface of the Sun in just a little more than 2 seconds.
1. plasma 2. pressure 3. equilibrium 4.convection 5. radiation 6. neutrinos
a star has a parallax angle p of .75 arcseconds. what is the distance to the star?
1.33 parsecs
The spectral type that denotes the coolest regular star is _____. Objects cooler than this are not considered stars, but are given the name _____________. These objects are very hard to observe because they are very faint in visible light, and put out most of their energy as _________. Eventually, new spectral types were used for these objects; the warmest of them are given spectral type __, while the coolest of them are given spectral type ___.
1.M9 2. Brown Dwarfs 3. Infrared rays 4. L 5. Y
conduction example
A pan on a stove, an iron, ice cube melting in hot cup of tea
Which statement correctly explains why convection occurs within a star, rather than all energy transport occurring as radiation?
Energy transport via radiation is not efficient enough because the high particle density prevents photons from traveling easily enough to escape; convection happens in order to help get the heat out.
Astronomers have discovered that the p-p chain of nuclear fusion that powers the Sun is pretty unusual among stars; most stars are NOT powered by this fusion process. True or False?
False
Deep inside the Sun, the process that gives the Sun the energy to shine is the fission of a helium nucleus into four hydrogen nuclei. True or False?
False
curium to plutonium uranium to lead Fusion or fission?
Fission
carbon to iron oxygen to neon helium to carbon boron to carbon fusion or fission?
Fusion
What are nonmetals to astronomers?
Hydrogen and Helium
Which method would you use to determine the distance to A star astronomers believe to be no more than 50 light-years from the Sun
Parallax
Which method would you use to determine the distance to A tight group of stars in the Milky Way Galaxy that includes a significant number of variable stars
Period-luminosity relation
Which method would you use to determine the distance to An asteroid crossing Earth's orbit
Radar ranging
A star must be hotter than about 25,000 K to produce an HII region. Which of the following types of stars would ionize the most hydrogen?
Spectral type O, Luminosity class V
Which method would you use to determine the distance to A star that is not variable but for which you can obtain a clearly defined spectrum
Spectroscopic parallax
From what you have learned about which kinds of stars produce emission nebulae and which kinds are associated with reflection nebulae, what can you say about the stars in this image?
The brightest stars visible are cooler than 25,000 K but hotter than 10,000 K
Which of the following statements correctly explains why HII regions appear red?
The red Hα line is the strongest emission line in the visible portion of the hydrogen spectrum.
Suppose a star's hydrostatic equilibrium is disrupted by a sudden drop in the energy generation rate in its core. Arrange the events listed below in the correct order that describes how the star responds to re-establish equilibrium.
The star will begin to contract as gravity exceeds outward gas pressure. Increased gravitational pressure heats up the core. Increasing core temperature boosts nuclear reaction rate. Higher energy generation rate increases gas pressure to balance gravity
Astronomers can use helioseismology, the study of the oscillations (or pulsations) in the Sun, to learn about the Sun's interior. True or False?
True
The most likely place that cosmic rays come from outside our solar system is supernova explosions (the explosions that mark the deaths of certain stars.) True or False?
True
When astronomers discuss a nebula, what are they talking about?
a giant cloud of gas and dust between or among the stars
What does E=mc^2 tell us?
a little bit of mass can be converted to a substantial amount of energy
visual binary
a pair of gravitationally bound stars that can both be seen with a telescope
an astronomer wants to observe a cloud of cold neutral hydrogen, far away from any stars. what would be an instrument that could help in this task?
a radio telescope, tuned to a wavelength of ~21 cm
the local bubble is:
a region of low density interstellar gas extending several hundred lightyears around the sun
what is an HII region?
a zone around a hot star where hydrogen atoms are ionized
redshift
an offset in the observed frequency of a wave, in the direction of longer wavelengths, due to relative motion between source and observer
blueshift
an offset in the observed frequency of a wave, in the direction of shorter wavelengths, due to relative motion between source and observer
what happens in the process of fluorescence?
atoms absorb ultraviolet rays and convert them to visible light as their electrons cascade to lower energy levels
how does conduction transport energy?
atoms or molecules collide with one another, transferring energy during the collision
What star is hottest?
blue
convection example
boiling water, downdraft of air in storm, warm air rising in atmosphere
How did Henrietta Leavitt "calibrate" her period-luminosity relationship for Cepheid variable stars? In other words, how did she make the general idea into a numerical rule?
by finding cepheids in star clusters whose distance was known in another way
radiation example
campfire warming you, cooking in easybake oven, microwaves in a microwave oven
blue
characterized by a visual color corresponding to wavelengths in the 450-475 nm range
red
characterized by a visual color corresponding to wavelengths in the 600-700 nm range
astronomers now understand that the dark regions or rifts in parts of our galaxy that are otherwise crowded with stars are caused by :
clouds with a considerable amount of dust which blocks the light of the stars behind them
molecular cloud description
cold and most dense
what factors affect the spectrum?
composition, rotation rate, atmospheric pressure, surface temperature
H2 regions description
cool and relatively dense
regions temp from coolest to hottest
coolest: interstellar hydrogen between the stars, the surface of the earth, the surface of the sun, HII region, ultra hot interstellar gas: hottest
surface temperature coolest to hottest by color
coolest: red, orange, yellow, white, blue: hottest
redder
corresponding to a wavelength that is longer than what it is being compared to
bluer
corresponding to a wavelength that is shorter than what it is being compared to
how does convection transport energy?
currents of heated fluid rise due to buoyancy, carrying energy to cooler levels
dimmest to brightest luminosity
dimmest: a type white dwarf, k type main sequence, g type main sequence, a type main sequence, m type supergiant: brightest
apparent brightness dimmest to brightest by color
dimmest: red, orange, yellow, white, blue: brightest
how does radiation transport energy?
energetic photons travel away from hot material and are absorbed by some other material, transferring their energy to it
what is chemical composition used for?
figure out the lines in the spectrum and see what elements they correspond to
Astronomers use the term interstellar medium to refer to?
gas and dust that lies between stars
Which kind of stars are best for measuring large distances?
high luminosity stars
cosmic rays are:
high-speed atomic nuclei, electrons, and positrons
supernova remnants description
hot and diffuse
HII regions description
hot and relatively low density
spectral classes, hottest to coolest
hottest: O, A, F, G, M T : coolest
what is mass used for?
in binary stars, measure periods, separations, and radial velocities
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
How would the apparent brightness of Alpha Centauri change if it were three times farther away?
it would only be 1/9 as bright
types of stars, least to most common
least: O, A, G, M: most
regions least to most dense
least: interstellar material in the immediate neighborhood of the sun, the typical interstellar material in our galaxy, a molecular cloud, sun, earth: most
electron, proton, neutrino, deuteron, helium-4: put in order from least to most mass
least: neutrino, electron, proton,deuteron, helium-4 :most
what is velocity toward or away from us used for?
measure the doppler shift of the lines in the spectrum
What is surface temperature used for?
measure the spectrum and determine the star's spectral type
what is diameter used for?
measure the way the star's light is blocked by the moon
Most of the stars we can see with the unaided eye from Earth are
more luminous (intrinsically brighter) than the Sun
Three stars are discovered which have parallax angles of 0.04, 0.002, and 0.0005 arcseconds. Arrange these in order of their relative distance from Earth, nearest to farthest.
nearest: .04 arcsec, .002 arcsec, .0005 arcsec : farthest
Two stars have the same luminosity, but star B is three times farther away from us than star A. Compared to star A, star B will look
nine times fainter
The Sun is an enormous ball of gas. Left to itself, a ball of so many atoms should collapse under its own tremendous gravity. Why is our Sun not collapsing?
nuclear fusion in the core keeps the temperature and the pressure inside the Sun at a high enough level so that gravity is balanced
if an astronomer wanted to find some relatively complex molecules in space, what technique should she use?
point a radio telescope into regions in the galaxy where there is a lot of dust
what color star has the most absorption bands?
red
Two stars have the exact same luminosity, but star Y is four times dimmer looking that star X. This means that
star y is twice as far away as star x
An astronomical unit is:
the average distance between the Earth and the Sun
A friend of yours who has not taken an astronomy class looks at your textbook and really likes the picture of the Pleiades, a cluster of stars surrounded by a bluish reflection nebula. She wants to know what causes that beautiful blue glow. To explain it to her, you want to compare the process that causes the blue glow to something that is in your friend's everyday experience. Which of the following terrestrial phenomena is the result of the same type of process that makes a reflection nebula in space?
the blue color of the Earth's sky
A friend (who does not have the new awareness which you have gained from this course) suggests that the mechanism that keeps the Sun shining as brightly as it does is the burning of coal. You brilliantly challenge his theory! Your challenge comes in several related steps; which of the following is one of those steps?
the dating of radioactive rocks show that the Earth and thus the Sun are billions of years old
What is the baseline that astronomers use to measure the parallax (the distance) of the nearest stars?
the diameter of the Earth's orbit around the Sun
you are observing a binary star system and obtain a series of spectra of the light from the two stars. in this spectrum, most of the absorption lines shift back and forth as expected from the doppler effect. a few lines, however, do not shift at all, but remain at the same wavelength. how can we explain the behavior of the non shifting lines?
the lines come from interstellar matter between us and the star, not from the stars themselves
The higher the luminosity (intrinsic brightness) a Cepheid variable is,
the longer the period of its variations
The term "baryon cycle," as astronomers use it, refers to
the movement of interstellar material into the Galaxy and into stars and then the movement out when stars end their lives
reddening
the selective removal of blue light from an object's observed spectrum due to dust scattering
Which of the following will show the smallest parallax shift?
the star 51 Pegasi, about 50 lightyears away
Alpha Centauri and the Sun have about the same luminosity. Which one appears brighter?
the sun
the dust in the dust clouds in interstellar space consists of:
tiny solid grains
