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113 terms

Astronomy 2012

University of Windsor Midterm
STUDY
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Which of these is not a form of electromagnetic radiation?
DC current from your car battery
The speed of light in a vacuum is
300,000 km/sec
If a wave's frequency doubles, its wavelength
is halved
What is the name of the temperature scale that places zero at the point where all atomic and molecular motion ceases
Kelvin
The sums observed psectrum is
a continuum with absorption lines
In Bohr's model of the atom, electrons
only make transitions between orbitals of specific energies
The total energy radiated by a blackbody depends on
the fourth power of its temperature
A jar filled with gas is placed directly in front of a second jar filled with gas. Using a spectroscope to look at one jar through the other you observe dark spectral lines. The jar closes to you contains
the cooler gas
In general, the spectral lines of molecules are
more complex than those of atoms
The two forms of EM radiation that experience the least atmospheric opacity are
light and radio waves
the observes spectral lines of a star are all shifted towards the red end of the spectrum. Which statement is true?
this is an example of the Doppler effect
Which of these is the same for all forms of EM radiation in a vacuum?
Velocity
Medium A blocks more of a certain wavelength of radiation that medium B. Medium A has a higher
Opacity
The primary purpose of a telescope is to
collect a large amount of light and bring it into focus
The angular resolution of an 8 inch diameter telescope is ____ greater than that of a 2 inch diameter telescope
4x
the amount of diffraction and thus the resolution of the scope depends on
the brightness of the object
what is the resolution of a telescope?
its ability to distinguish two adjacent objects close together in the sky
compared to a 5 inch prime focus reflector, a 5 inch Newtonian reflector will
have the same light gathering power
What is the light gathering power of an 8 inch telescope compared to a 4 inch?
4x better
Green light has a shorter WL than orange light. In a 5 inch telescope, green light will
provide better angular resolution than orange light
What problem does adaptive optics correct
Turbulence on the earths atmosphere that creates twinkling
Most radio telescopes are laid out which optical telescope design?
Prime focus reflector
in astronomy, interferometry can be used to
improve the angular resolution of the radio telescopes
The temperature of the photosphere is about
5,800K
What is the meaning of the solar constant?
the amount of energy the Earth receives per unit area and unit time
What two energy transport mechanisms, in order from outside the core to the surface, are found in
the Sun?
radiation, convection
The outward pressure of hot gas in the Sun
is balanced by the inward gravitational pressure.
The solar winds blow outward from
coronal holes
From inside out, which is in the correct order for the structure of the Sun?
radiative zone, convective zone, chromosphere
How long does the sunspot cycle last, on average?
about 11 years
Visible sunspots lie in the
granualtion in the photosphere
As the Sun rotates, an individual sunspot can be tracked across its face. From eastern to western
limb, this takes about
two weeks
The most striking example of solar variability was the
Maunder Minimum from 1645-1715
Sunspots
come in pairs representing the north and south magnetic fields
During a period of high solar activity, the corona
is more irregular
Sunspots are dark splotches on the Sun. Which statement is true?
they are extremely hot, but cooler than the surrounding areas of the sun
While observing the Sun, you note a large number of sunspots. What can you conclude?
There are likely to be an above average number of flares and prominences.
The critical temperature to initiate the proton-proton cycle in the cores of stars is
10 million K.
In the proton-proton cycle, the helium atom and neutrino have less mass than the original
hydrogen. What happens to the "lost" mass?
It is converted to energy.
The primary source of the Sun's energy is
the strong force fusing hydrogen into helium.
In the proton-proton cycle, the positron is
an anti-electron.
Which is the net result of the proton-proton chain?
4 protons = 1 helium 4 + 2 neutrinos + gamma rays
Hydrogen "burning" by fusion reactions occurs only in the deep interior of the Sun (and
other stars), because
this is the only place in the Sun where
the requisite conditions of high temperature and high density occur
What happens to the positrons produced by the nuclear reactions in the core of the Sun?
they collide with electrons, producing energy
Which of these are not associated with the active Sun?
granulation
Which statement about stellar motion is incorrect?
proper motion is measured in intervals of 6 months
A star has a parallax of 0.01 arc seconds. Its distance is
100 parsecs
If Vega is apparent magnitude zero, and Deneb first magnitude, then
vega must be 2.5x more luminous than deneb
A star's absolute magnitude is its apparent brightness as seen from
10 parsecs distance
Two stars both have parallaxes of 0.023", but star A has apparent magnitude +2.3, while star B is
magnitude +7.3. Which statement is true?
star A is both 100x brighter and more luminous than star B
What physical property of a star does the spectral type measure?
temperature
Which of these stars would be the hottest?
B0
(B0, M10, k9,g2,a0)
What can be said with certainty about a red star and a blue star?
the blue star is hotter than the red star
Compared to a type A0 star, a type A9 star is
cooler
the star's color index is a quick way of determining its
temperature
The H-R diagram can plot
temperature vs. luminosity
In the H-R diagram, what are the two most important types of data plotted?
spectral classes and absolute magnitudes
On the H-R diagram, the Sun lies
about the middle of the main sequence
On the H-R diagram, white dwarfs Sirius B and Procyon B lie
at the top left
On the H-R diagram, red supergiants like Betelgeuse lie
at the top right
A star near the lower right of the H-R diagram is likely to be
red, with low illuminosity
The Doppler shift is used to find
spectroscopic boundaries
Which type of binary do we get information about by looking at the intensity of light?
eclipsing
Binary stars separated enough to be resolved in a telescope are called
visual binaries
apparent angular movement of a nearby star against the background stars as a consequence of
its motion in space is known as
proper motion
The speed of a star, measured in a direction perpendicular to the line of sight from the Earth to the
star, is known as
transverse velocity
Suppose that two identical stars (having the same total light output or luminosity) are located such
that star A is at a distance of 5 pc and star B is at a distance of 25 pc. How will star B appear,
1/25 as bright
Light, leaving a point source, spreads out so that the apparent brightness, I , of light per unit area
varies with distance d according to which law (μ means "proportional to")?
A) I µ 1/d 2
Interstellar gas is composed mainly of
90% hydrogen, 9% helium by weight.
What happens to light passing through even thin clouds of dust?
It dims and reddens the light of all more distant stars.
Which statement about dark dust clouds is true?
They can be penetrated only with longer wavelengths such as radio and infrared.
Some regions along the plane of the Milky Way appear dark because
stars in that region are hidden by dark dust particles.
Emission nebulae like M42 occur only near stars that emit large amounts of
UV radiation
what is the primary visible color of an emission nebula?
red due to ionized hydrogen atoms
Due to absorption of shorter wavelengths by interstellar dust clouds, distant stars appear
larger
The spectra of interstellar gas clouds show that they have the same basic composition as
stars
Which statement is true about the interstellar medium?
We know more about the gas than the dust.
The density of interstellar dust is very low, yet it still blocks starlight because
the dust particles are about the same size as the light waves they absorb.
What two things are needed to create an emission nebulae?
hot stars and interstellar gas, particularly hydrogen
A large gas cloud in the interstellar medium that contains several type O and B stars would appear
to us as
an emission nebulae
Neutral hydrogen atoms are best studied from their energy given off as
21-cm waves in the radio region.
Complex molecules in the interstellar medium are found
primarily in the dense dust clouds
Why are dark dust clouds largely misnamed?
the contain much more gas than dust
The average temperature of the typical dark regions in space are
100K
Interstellar dust clouds are best observed at what wavelength?
radio
Which of these is not a consequence of dust in the interstellar medium?
red light from the emission nebulae
It is important to study interstellar dust because
A) there is almost as much mass between the stars as therre is in them.
B) this is where stars are formed.
C) old stars expel their matter here when they die.
D) all of the above.
Reflection nebula have their blue colour because
the interstellar dust deflects the blue light.
What is true of emission nebula?
A) they are often part of much larger interstellar clouds.
B) their temperature can exceed that of our sun.
C) they are bigger than earth.
D) they produce an emission spectrum.
E) All of the above.
When an electron in hydrogen changes its spin from the same to the opposite direction as the
proton, it
emits radio wave photon
During the T-Tauri phase of a protostar, it
may develop very strong winds.
What is the critical core temperature required for fusion?
10 million K
Which statement about the stages of starbirth is false?
*A) nuclear reactions begin in the core by stage 4.*
B) The T-Tauri wind is prevalent in stage 5.
C) By stage 3, the star has formed a photosphere.
D) At stage 1, only the cloud exists.
E) By stage 7, the star has reached the main sequence.
On an H-R diagram, a protostar would be
above and to the right of the main sequence.
The single most important determinant of the temperature, density, radius, luminosity,
and pace of evolution of a protostar is its
mass
A cloud fragment too small to collapse into a main sequence star becomes a
brown dwarf
All globular clusters in our Milky Way are about how old?
around 10 billion years old
Why are star clusters ideal "laboratories" for stellar evolution?
Their stars are all about the same age, composition, and distance from us.
Which of these would typically be the brightest star in a young open cluster?
B1V
What are the characteristics of an open cluster of stars?
a few hundred, mostly main-sequence stars
Which of these would be the brightest star in an ancient globular cluster?
K3
Which is characteristic of globular star clusters?
old age and hundreds of thousands of stars, only about 50 pc wide
How long does it take an M-type star to reach the main sequence, compared to a
solar-type star?
about twenty times longer
A fragment of a collapsing gas cloud that comes to equilibrium with a central
temperature of 4 million K will become a
brown dwarf
Why are the majority of stars in the sky in the main sequence phase of their lives?
This is the longest-lasting phase in each star's life.
Which of the following statements about the rate of stellar evolution is true?
The more massive the original star, the faster the evolution.
Which of the following are NOT very young stars or prestellar objects?
red giants
Within a globular cluster, what would you expect to find in the population of stars?
many red giants, white dwarfs, and dim red stars but no bright blue stars or dust
and gas
ZAMS stands for:
zero age main sequence
In what stage of evolution is a star formed?
stage 6
In what stage of evolution is the forming star the brightest?
stage 4
What is the importance of nebular clouds that surround newly forming stars?
They add mass to the star during formation.
What is NOT true of successful star formation?
Planets are formed out of the nebular cloud.