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okstate ASTRO spring final
ASTR 1024 Stars, Galaxies, Universes - note cards for final exam based on old test answers and book notes
82
Astronomy
Undergraduate 1
05/01/2013

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Term
Cosmology
Definition
the study of the origin, present structure, evolution, and destiny of the universe
Term
Cosmological models
Definition
mathematical descriptions that try to explain how the universe began, how it is changing as time goes by, and what will happen to it in the future
Term
evolutionary and steady state
Definition
the two types of basic types of cosmological models
Term
Cosmological redshift
Definition
a phenomenon that is caused by shift in red wavelengths of moving objects in the galaxy
Term
Hubble law
Definition
states that a galaxy's velocity of recession, v, is directly proportional.

v = Hd

This is a constant
Term
Cosmological principle
Definition
the universe is both homogeneous and isotropic
Term
Big Bang theory
Definition
13.7 + 1% billion years ago our universe expanded rapidly from an infinitely hot, dense state and has been evolving since
Term
open universe model
Definition
the universe will continue expand indefinitely
Term
flat universe model
Definition
predicts a continuing to expand indefinitely
Term
closed universe
Definition
if gravity acts alone the universe will not expand forever, but will contract until all matter is crushed again into a hot, dense state
Term
Big Crunch
Definition
universe will contract until all matter is crushed again into a hot, dense state
Term
perfect cosmological principle
Definition
says the universe is the same everywhere on the large scale, at all times (Steady State Theory assumes this)
Term
critical density
Definition
the minimum average density of matter and energy required to make the universe flat
Term
cosmological constant
Definition
dubbed dark energy, equivalent to a cosmic repulsion, may drive an ever accelerating expansion
Term
Cosmic background radiation
Definition
thought to exist due to the Big Bang
Term
Hubble Radius
Definition
the size of the observable universe, and is equal to the speed of light divided by the Hubble constant, so c/H
Term
Astrobiology
Definition
the study of the origin, distribution, evolution, and future of life in the universe
Term
Heliopause
Definition
the area where both Voyagers are currently and is considered the edge of our solar system
Term
all-sky survey
Definition
searches the entire sky over a wide frequency range to detect strong signals
Term
high-sensitivity target search
Definition
seeks weak signals originating near close stars like our Sun
Term
A teaspoon in a glass of water appears to be broken or bent at the water line because of
Definition
refraction
Term
5. Which important characteristic of a telescope that is used for visual observations can be altered simply by changing the eyepiece?
Definition
Magnifying power
Term
rule of 72
Definition
72/interest rate
Term
The General Theory of Relativity has been experimentally supported by
Definition
observing shifts in star positions near the eclipsed Sun
Term
7. The Andromeda spiral galaxy is about three million light years away. Therefore,
Definition
we are seeing the galaxy as it was three million years ago.
Term
The famous equation E = mc2, which describes the potential energy content E of any given mass m, fully explains
Definition
the mass losses in the Sun’s hydrogen fusion reactions, creation of particles having mass by the collisions of energetic photons, and mass losses in the uranium-fission reactions of powerplants
Term
One of the first persons known to conduct experiments to investigate natural phenomena such as the behavior of falling objects, as opposed to only thinking about them, was
Definition
Galileo
Term
The distance of 0.001 m would be written in scientific notation as
Definition
10-3 m
Term
15. Who mathematically derived Kepler’s three laws of planetary motion from the laws of universal gravitation and of the conservation of angular momentum?
Definition
Newton
Term
If you were standing on the Earth’s South Pole, the North Star (Polaris) would be
Definition
at your nadir
Term
The people responsible for preserving much ancient Greek, astronomical knowledge, refining it, and passing it on to the Europeans (which helped launch the Renaissance) were the
Definition
Arabs
Term
A planet’s gravity will curve the paths of passing _____ that were originally moving in straight lines
Definition
rocks and light rays
Term
The celestial sphere is a model of the sky that astronomers (and the Voyager 4 computer program) use to compute the appearances of celestial phenomena. However, one error of this model, usually of no importance, is that all stars are taken to be equally
Definition
distant
Term
A new, large optical telescope, such as the 10-meter diameter Keck I reflector in Hawaii, costs about as much money as
Definition
a jumbo jet airliner
Term
Which word below best matches this definition: “An explanation for a fundamental natural phenomenon, based on physical law as currently understood, which has passed every experimental test thus far.”?
Definition
Theory
Term
A star with a right ascension of 3h 10m and a declination of +1* 10’ would be located very close to the
Definition
celestial equator.
Term
You are watching a spaceship fly past you at a speed for which the Lorentz factor у (gamma) equals 2. You measure that the moving ship is 1000 m long as it passes abreast of you. The ship then stops and lands near you. You remeasure the stationary spaceship, and find that its length is actually
Definition
2000 m
Term
Optics tells us that the smallest angle θ (in arcseconds) that a telescope of diameter d (in mm) can resolve is given by θ = 116/d. The OSU observatory’s telescope is about 600 mm in diameter. Therefore, θ for that telescope is about
Definition
1/6 arcsec
Term
The famous mnemonic device, “Oh, be a fine girl (guy), kiss me!”, was devised at the beginning of the 20th century by Dr. Henry Norris Russell, a Princeton astronomer. It is used to recall the proper order of
Definition
stellar spectral types
Term
In class you viewed the light and spectrum from an incandescent light bulb connected to a variable-voltage power supply. As the voltage was increased to make the bulb’s filament hotter, the bulb’s light output and spectrum became
Definition
brighter and bluer
Term
Assume that four stars, of spectral types A, M, G, and O, are all on the main sequence. According to the mass-luminosity relation, the least massive of these is of spectral type
Definition
M
Term
On a Hertzsprung-Russell Diagram, ___ is the horizontal axis, while ___ is the vertical axis.
Definition
temperature, luminosity
Term
A star’s proper motion is measured in units of ___ and is due to a star’s having a nonzero ___ relative to the Sun.
Definition
arsec/yr, tangential velocity
Term
Relative to the Sun, nearby stars move with velocities of roughly
Definition
10 km/sec
Term
When an electron in a hydrogen atom “falls” from a higher energy level to a lower energy level, the atom
Definition
emits light
Term
Sunspots appear dark because they are
Definition
cooler than the photosphere
Term
9. The tiny, solid particles called dust that are often mixed in with the gas between the stars are commonly composed of carbon or silicon, meaning that they are like ___ in composition, respectively
Definition
soot or sand
Term
Imagine a binary star that consists of two main-sequence stars, one green and the other orange. The green star is more massive than the orange one. Where is the binary’s center of mass located?
Definition
Nearer the green star
Term
11. Which type of ground-based telescope can easily observe astronomical objects in the daytime as well as at night?
Definition
Radio
Term
12. The total amount of energy radiated per second by a star can either be described in terms of its ___ in Watts, or by its ___, which is a unitless number that can be thought of as a ranking.
Definition
luminosity, absolute magnitude
Term
Which color of light is characterized by the highest energy?
Definition
Blue
Term
Those features at the surface of the Sun which are reddish, up to 104 km tall, and almost look like giant blades of grass are called
Definition
spicules
Term
A continuous, synchrotron spectrum is emitted by astronomical objects such as radio galaxies that contain ___ spiraling in intense ___ fields.
Definition
electrons, magnetic
Term
17. The parallax angle of a star is observed to be 0.2 seconds of arc. By computing the reciprocal of this number, we find that its distance from us is
Definition
5 pc
Term
Which of the following luminosity class suffixes refers to stars of the supergiant type?
Definition
I
Term
21. When you determine the temperature of the Sun from its prominent optical spectrum, you are specifically measuring the temperature of its
Definition
photosphere.
Term
22. The nearby stars are mostly main-sequence (MS) stars of spectral type M because M stars
Definition
live longer than other MS stars, so their numbers accumulate.
Term
23. The apparent magnitude a star would have if it were 10 pc from Earth is called its ___ magnitude.
Definition
absolute
Term
24. The solar wind
Definition
has an average temperature of about 100,000 K.
Term
In a supernova explosion, the outer layers of the star are ejected into space by the outwardly moving
Definition
shock wave.
Term
2. Suppose that own a white dwarf star “weighing” 1.1 solar masses. You add enough material to the star to increase its mass to 1.2 solar masses. Because the white dwarf’s electrons are degenerate, it will ___ in diameter and the temperature of its electrons will ___ to support the star’s added weight.
Definition
shrink, not change
Term
4. You can estimate the mass of a distant spiral galaxy if you pick out a star near the edge of the galaxy’s disk, and can measure the star’s orbital speed (around the galaxy’s center) and the star’s
Definition
distance from the galaxy’s center.
Term
5. In the study of star clusters, it is reasonably assumed that the stars within a given cluster differ significantly from each other only in
Definition
mass.
Term
6. The forces of gas pressure and of gravity are normally balanced at every point within a star. If, for some reason, the internal gas pressure decreases (for example, as the nuclear fuel in the core is exhausted), then the star will initially
Definition
shrink in radius.
Term
7. Which of the following would be the best distance indicator for the most distant galaxies?
Definition
The Doppler shifts of galactic spectra
Term
8. If the Moon were to instantly turn into a black hole of the same mass, it would
Definition
orbit the Earth as usual.
Term
9. When stars leave the main sequence on the H-R diagram, their outer envelopes (layers) expand immensely, so these stars become both
Definition
cooler and brighter.
Term
10. A galaxy that looks like a perfectly symmetrical sphere would be given which code designation?
Definition
E0
Term
11. The probability of one’s galaxy colliding with another galaxy within the same cluster of galaxies is
Definition
much higher than (a) [the same as that of two stars’ colliding within a galaxy]
Term
12. The imaginary part of a non-rotating black hole that is spherical and whose radius equals the Schwarzschild radius, the radius at which the escape speed equals the speed of light, is the
Definition
event horizon.
Term
13. Hypotheses about the production of light pulses and / or radio “beeps” by a pulsar all rely on the existence of ___ in the pulsar’s rotating ___
Definition
asymmetry, magnetic field
Term
14. Population I stars are metal-rich, while Population II stars are metal-poor. In our own Milky Way Galaxy,
Definition
Population I stars are found in the disk.
Term
15. The reddening of starlight (the removal of shorter wavelengths) as it travels through our Galaxy to us is mainly due to the presence of ___ in the interstellar medium along the route of travel.
Definition
dust
Term
16. Supernova remnants emit large quantities of synchrotron radiation detectable at radio wavelengths. Therefore, we know that these remnants contain ___
Definition
high-speed electrons.
Term
17. Which of the following might one not expect to see at some time around a star that is being “born”?
Definition
rings of ice and cold dust perpendicular to the object’s equator.
Term
19. The glowing bubble or “hourglass” of gas that cnstitutes a typical planetary nebula came from the
Definition
outer layers of a dying, red-giant star.
Term
20. The amount of fuel that a star has to “burn” is proportional to its mass, while the rate at which that star consumes its fuel is proportional to its luminosity. Therefore, a star’s fuel-burning lifetime is proportional to its
Definition
mass divided by its luminosity.
Term
21. What “holds up” a black hole against the inward force of gravity?
Definition
No known pressure
Term
22. In the process called “electron capture” that leads to the explosion of the most massive stars, a proton and an electron are forced together to form a neutrino (electric charge zero, mass almost zero) and one ___. Hint: consider the conservation of electric charge.
Definition
neutron
Term
23. Recurring nova explosions are possible in a binary star system whose primary star is a red giant and whose secondary star is a ___. The two stars must be close enough together for a mass to flow from the ___ to the other star.
Definition
white dwarfprimary
Term
24. Which of the following exists almost exclusively in the halo of the Milky Way?
Definition
Globular star clusters
Term
25. A neutron star is a neutron-rich object about as massive as the Sun but which as small in diameter as
Definition
a city like Stillwater.
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