Astronomy Chapt. 3
The most distant stars we can measure stellar parallax for are approximately:
100 parsecs away
In a visual binary system with circular orbits, if in 20 years the two stars' position angles have shifted by 30 degrees, the pair's period must be:
240 years
An atom of the element iron has an atomic number of 26 and an atomic mass number of 56. If it is neutral, how many protons, neutrons, and electrons does it have?
26 Protons, 30 Neutrons, 26 Electrons
How much electrical charge does an atom with 6 protons, 6 neurons, and 5 electrons have?
A positive charge of + 1
Astronomers have discovered stars even cooler that the traditional spectral type M stars recently. Astronomers have given these colors stars a new spectral type, L. If you wanted to go out and find more such type L stars, what kind of instrument would it be smart to use?
A sensitive infra-red telescope.
A star moving towards the Sun will show:
A shift in the spectral lines toward the blue end (as compared to the laboratory positions of these lines)
Which of the following looks the brightest in the sky?
A star with magnitude-1
Which of the following can astronomers NOT learn from studying the spectrum of a star?
All of the above can be learned from studying the spectrum.
The apparent magnitudes, the absolute magnitudes, the spectral classes, and the parallaxes of these following stars respectively are:
Alpha Cent
When white light passes through a cool cloud of gas, we see:
An absorption line spectrum.
When an atom absorbs a photon containing energy, any of the following can happen except which?
An electron moves from an upper energy level to a lower one.
An artist who likes working with sources of light decides to make a modern sculpture out of electrified glass tubes that contain very thin (rarified) neon gas. When the sculpture is finished, and the electricity is turned on, the tubes glow with a rich red color. What we are seeing is:
An emission spectrum
The astronomer who, at the turn of the century, measured the spectra of hundreds of thousands of stars, leaving a catalog that astronomers used for the rest of the century, was:
Annie Cannon
Why are astronomers much more interested in the luminosity of a star than its apparent brightness?
Because the luminosity tells us how bright a star really is, while apparent brightness only tells us how bright it happens to look from Earth.
Why do different types of atoms (elements) give off or absorb different spectral lines?
Because the spacing of the energy levels is different in different atoms.
Which color star is likely to be the hottest?
Blue-violet
At an astronomical conference, an astronomer gives a report on a star that has recently begun to interest astronomers because of hints that it may have a planet around it. In his report the astronomer gives the average speed with which this star is moving away from the Sun. How did the astronomer measure this speed?
By looking at the Doppler shift in the lines of the star's spectrum.
Which of the following persons used the ideas of quantum mechanics to describe why the spectral classification scheme is in order of decreasing temperature?
Cecilia Payne-Gaposchkin
By which appropriate method the chemical composition of a star can be deduced from its spectrum?
Characteristic lines
In comparing first magnitude Deneb with second magnitude Polaris, we find that:
Deneb appears 2.5 times brighter to us than does Polaris.
By which appropriate method the radial velocity of a star can be deduced from its spectrum?
Doppler Shift
In a spectroscopic binary, if a pair shows a combined set of lines tonight, but a maximum split two nights later, its orbital period must be:
Eight days
Which of the following statements about elections is not true?
Electrons orbit the nucleus rather like planets orbiting the Sun.
When an electron in an atom goes from higher energy state to a lower energy state, the atom:
Emits a photon of a specific frequency
Which of the following statements about photons is FALSE?
High energy photons have a high frequency.
Perhaps the greatest of the Greek astronomers, __________ compiled the first catalog of stars, accurately measured their positions, and defined the basic system of stellar brightnesses.
Hipparchus
If hydrogen is the most common element in the universe, why do we not see the lines of hydrogen in the spectra of the hottest stars?
In the hottest stars, hydrogen atoms are ionized, and so there are no electrons to produce lines in the spectrum.
By which appropriate method the gas density, axial rotation, and magnetic field of a star can be deducted from its spectrum?
Line shape
How do astronomers learn what elements are present in a given star?
Look at the absorption lines in its spectrum
After days and days of work, a group of graduate students has finally measured the wavelengths of hundreds of lines in the spectrum of a distant star. If a number of the lines come from molecules such as titanium oxide, the star is likely to be which spectral type:
M
Which of the following types of star is the coolest (has the lowest surface temperature)?
M
The idea that atoms radiate energy only when their electrons move from higher to lower energy levels was first advanced by:
Niels Bohr
Two stars have the same luminosity, but star B is three times farther away from us that star A. Compared to star A, star B will look:
Nine times fainter
The light from an object moving tangentially ( to your left or right ) will exhibit:
No shift
The motion of a star across the sky (perpendicular) to our line of sight) is called its
Proper motion
The apparent magnitudes, the absolute magnitudes, the spectral classes, and the parallaxes of these following stars respectively are:
Proxima
Suppose you built a scale-model atom in which the nucleus was the size of a tennis ball. About how far would the cloud of electrons extend?
Several kilometers
The apparent magnitudes, the absolute magnitudes, the spectral classes, and the parallaxes of these following stars respectively are:
Sirius
By which appropriate method the temperature of a star can be deduced from its spectrum?
Spectral class type
Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts?
Spectroscopic Binary
Star A and star B have the same temperature, but star B is more luminous that star A. What can you infer about these two stars?
Star B must be bigger.
The absolute magnitude of a star is its brightness as seen from a distance of:
Ten parsecs
In general, the narrower the spectral line of star:
The bigger the star is.
If one object has a large redshift and another object has a small redshift, what can we conclude about these two objects?
The one with the large redshift is moving away from us faster than the one with the small redshift.
If we observe one edge of a planet to be redshifted and the opposite edge to be blue shifted, what can we conclude about the planet?
The planet is rotating.
The depth of the dip in a star's brightness due to the transit of a planet depends most directly on:
The planet's size
Which of the following could not be determined by an observation that uses only spectroscopy?
The size of a distant galaxy
The apparent magnitudes, the absolute magnitudes, the spectral classes, and the parallaxes of these following stars respectively are:
Thuban (m = 4.7, M = 5.9, spectral class:K, q = 0.173")
Which of the following terms is given to a pair of stars that appear to change positions in the sky, indicating that they are orbiting one another?
Visual Binary
Which of the following statements about spectral types of stars is true?
all of the above are true
Astronomers arrange the stars into groups called spectral classes (or types) according to the kinds of lines they find in their spectra. These spectral classes are arranged in order of:
decreasing surface temperature.
A team of astronomers takes spectra of thousands of different stars in different parts of the sky. The spectra show significant differences. The main reason the spectra of the stars do not all look alike is that their stars
have different temperatures.
When an astronomer rambles on and on about the luminosity of a star she is studying, she is talking about:
how much energy the star gives off each second.
A graduate student has spent a whole year doing a careful analysis of the spectrum of a star . While she has found lines from many elements, there was not a trace of the element helium in the spectra she has been analyzing. From this she can now conclude:
since helium shows lines only in hot stars, this star must be relatively cool.
