UNC Astr101
The 6.5-meter diameter Webb telescope will resolve sources of 1-micron wavelength light to...
0.038 arcseconds
Chandra, NASA's X-ray observatory, orbits Earth in a highly eccentric orbit that goes ≈1/3 of the distance to the moon. Since the orbit is highly eccentric, the semi-major axis is then ≈1/6 of the Earth-Moon distance. What is Chandra's orbital period in lunar months?
0.07 lunar months
A Jupiter-mass extrasolar planet is observed to orbit a 1-solar mass star every 10 days. What is the semi-major axis of the planet's orbit?
0.091 AU
The mass of the moon is 0.012 Earth masses. The radius of the moon is 0.27 Earth radii. The escape speed from the surface of the moon is what fraction of Earth's?
0.21
When Venus is at closest approach to Earth, it takes 270 seconds for radio waves to be transmitted to Venus, bounce off of Venus, and return to Earth. Given this, compute how many meters are in an AU?
1.5 x 10^11 m
How much more light does one collect with a 10-meter diameter telescope in 10 minutes than with a 1-meter diameter telescope in 100 minutes?
10 times as much
The wavelength of a 3 × 10^15 Hz gamma ray is:
100nm
How many mm are in a micro-m?
10^-3
You watch the constellation Orion rise above the horizon at 2 AM. At what time will you have to go out to watch it rise two months later?
10pm
Consider a slowly rotating world with a very thick atmosphere. What is the temperature anywhere on the planet, if the planet orbits 2 AU from the sun and reflects 50% of incoming light back into space?
165K
Planet X is observed to have a small moon. This moon is observed to orbit the planet once per month at a distance of 15 Planet X diameters. What is the mass of Planet X in solar masses? [Hint: Use Newton's form of Kepler's Third Law: P2 is proportional to a3/M, where M is the mass of Planet X (assuming that the mass of the moon is negligible in comparison).]
2.5 x 10^-4 solar masses
At perihelion, Mars is 1.38 AU from the sun. At aphelion, Mars is 1.67 AU from the sun. Calculate how much the average surface temperature on Mars drops from when at perihelion to when at aphelion? (On average, Mars reflects 25% of incoming light back into space.)
20K
Prof. Reichart's wife is way hotter than he is. Four times hotter to be precise. How much more energy does she emit per unit time per unit surface area?
256
1/8th of a radioactive element's atoms remain in a lunar rock sample. How many half lives old is the rock?
3
Triton currently orbits Neptune at a distance of 350,000 km, but because of tidal forces it is slowly moving closer to Neptune. If Triton is approaching Neptune at a rate of 8.0 cm per year, how long until it enters Neptune's Roche limit and breaks apart into great rings like Saturn's? (Neptune's radius is 25,000 km.)
3.6 billion years
Although robots have largely taken the place of humans for travel to the moon and beyond, humans will likely return to the moon someday. Where should we land? Calculate how hot it gets when the sun is directly overhead. (The moon reflects 12% of incoming light back into space.)
381 K
The small world Quaoar is observed to orbit the sun once every 285 years. What is the semi-major axis of its orbit?
43.3AU
A bright star circles the south celestial pole for 3 hours. Through what angle has it moved?
45 degrees
Astronomers have found a new object. With respect to background stars, it appears to move 1/60th of a degree over the course of six months, followed by a return to its original position over the course of the next six months. How close is it to Earth?
6,900AU
Planet X is in a circular orbit. Given the measurement of the AU from bouncing radio waves off of Venus, what is the distance to Planet X in meters when at closest approach to Earth?
6.6 x 10^12 m
Tides are highest
On the side of Earth that is facing the moon & On the side of Earth that is facing away from the moon & When the moon is new or full
The day is 12 hours long and the night is 12 hours long:
On the vernal and autumnal equinoxes
Which of the following statements is not true
One chlorine atom destroys approximately 100 ozone molecules
Divisions and gaps within Saturn's rings are caused by
Orbital resonances with Saturn's moons & Small moons within the rings
You send a message to Prof. Reichart's good friend Buzz Aldrin on the moon, 384,000 km away, and he sends you an immediate reply. Both messages travel at the speed of light. How long do you have to wait between sending your message and receiving his?
Over 2 seconds
What is the ideal shape for a single mirror to reflect and focus parallel rays of light to a point?
Parabolic
A hydrogen atom is in an excited state! Its electron decays from the fourth excited state to the second excited state. What type of photon is released?
Paschen beta
Detector technology in use from the 1920s to the 1970s
Photographic plate
In 26,000 years...
Polaris will be the pole star.
Single-mirror telescope design
Prime
Perfected the geocentric model of the universe:
Ptolemy
Which of the following is an adaptive optics design?
Rapidly moving small mirror & Rapid imaging and computing & Artificial guide star
Which of the following was not considered to be strong evidence for the wave nature of light?
Refraction
A planet is measured to have a density of 3,500 kg/m^3. It is composed primarily of
Rock
Terrestrial planets did not form in the outer solar system because
Rocky material did accrete in the outer solar nebula, but so did a far greater number of water, ammonia, and methane molecules
How much more light does one collect with a 100-meter diameter telescope in 10 second than with a 1-meter diameter telescope in 100,000 seconds (nearly 28 hours)?
Same amount
Which of the following statements are true?
Since Venus is closer to the sun than Earth, its surface was hotter and consequently its water vapor could not condense into oceans, but instead remained atmospheric. Since water vapor is a greenhouse gas, this increased Venus's surface temperature. & Since Venus did not have standing water to help incorporate its atmospheric carbon dioxide into rocks, it remained atmospheric. Since carbon dioxide is a greenhouse gas, this increased Venus's surface temperature. & Earth's oceans help to incorporate Earth's atmospheric carbon dioxide into rocks. This is balanced by plate tectonics and volcanic activity, which returns carbon dioxide to Earth's atmosphere. & Since Mars is farther from the sun and smaller than Earth, its interior cooled more quickly, resulting in no plate tectonics and reduced volcanism. & Carbon dioxide in Mars's early atmosphere was absorbed by standing water and incorporated into rocks, but was not fully replenished by Mars's less active volcanoes. Since carbon dioxide is a greenhouse gas, this decreased Mars' surface temperature. & As Mars's surface temperature dropped, water vapor froze out of Mars's atmosphere. Since water vapor is a greenhouse gas, this further decreased Mars's surface temperature.
This picture (complete circle of stars around center, where there is no star directly above) was taken at the:
South Pole
Carried seven astronauts per mission
Space Shuttle
Which NASA spacecraft would you chose to observe a 100K cloud of gas? (Spitzer, Hubble, Chandra, Fermi)
Spitzer (100K objects emit in the far infrared)
If the mass of the sun, the mass of Earth, and the sun-Earth distance all doubled, the force of gravity between the sun and Earth would:
Stay the same
The human eye is
A refracting telescope with color and monochromatic detectors
Smallest dwarf planet
Ceres
Which of NASA's four "Great Observatories" uses mirrors that look like nested barrels?
Chandra
Select all that apply. Which of the following is found in modern spectrographs?
Charge-coupled device (CCD) and Diffraction grating
Impacts of comets and/or asteroids large enough to level major cities
Continue to occur every thousand years or so
Extrasolar planets around sun-line stars have been discovered by
Direct imaging & Doppler method & Gravitational microlensing & Transit method
You take a spectrum of a star. Which of the following cannot be used to measure its surface temperature?
Doppler shift of spectral lines
Dust played the following key role in the formation of the solar system
Dust helped to cool the solar nebula & Dust seeded the accretion of atoms and molecules into planetesimals.
Convection occurs in
Earth's asthenosphere & Earth's troposphere
Differentiation is responsible for
Earth's core being denser than its mantle & The moon's core being denser than its mantle & The moon's core being offset toward Earth & The moon's mantle being offset toward Earth & Maria only on the near side of the moon
This layer is solid, but not by pressure
Earth's lithosphere
Earth's magnetic field is generated by
Earth's outer core
Contains Earth's ozone layer
Earth's stratosphere
The medium in which X rays propagate:
Electromagnetic field
The medium in which light waves propagate:
Electromagnetic field
When it is spring in the southern hemisphere, it is what in the northern hemisphere?
Fall
Astronomical telescopes assume that the incoming rays of light are nearly parallel. This is true if the source of light is:
Far enough away that the distance might as well be infinite
Consider a simple refracting telescope. Images will be...
Flipped compared to what is in the sky
Which of the following statements is true?
Gravity flattened the solar nebula into a disk and as it contracted its rotation rate increased.
Light from a star passes through a cold, transparent hydrogen cloud on its way to Earth. We receive a:
Hydrogen absorption line spectrum
Select all that apply. Consider a generic Jovian planet with a cloud-top "surface" temperature of 85 K and an escape speed of 35 km/s. Assuming that the planet was not any hotter in the past, calculate if its atmosphere contains significant amounts of:
Hydrogen gas (H2) & Helium gas (He)
Lunar formation theory that also explains the tilt of Earth's rotation axis
Impact theory
Which lunar formation theory is considered to be most likely?
Impact theory: When Earth was still molten, a Mars-sized object struck it and debris that was thrown off into space pulled itself together gravitationally and formed the moon
Given the diameter, mass, and density of Planet X, it is probably a:
Jovian planet similar to Saturn
Mimas is to the Cassini division as
Jupiter is to the Kirkwood gaps
First to discard the ancient aesthetic ideals of uniform and circular planetary motion:
Kepler
A hydrogen atom in an excited state emits a Balmer beta photon followed by a Lyman alpha photon. The electron decayed from:
The third excited state to the first excited state to the ground state
Since the line of nodes regresses:
There are ~19 eclipse seasons every 9 tropical years
Your eye is a refracting telescope that operates at a wavelength of ≈500 nm. Your pupil is ≈2 mm across. What is the resolving power of your eye?
~1 arcmin
With adaptive optics turned off, UNC's 4.1-meter diameter SOAR telescope resolves sources of ≈500-nm wavelength light to:
~1 arcsec
Consider the moon rocks that the crew of Apollo 11 brought back from Mare Tranquillitatis. Within the zircon crystals within these rocks, we find approximately 15 atoms of 207Pb for every atom of 235U. How old is Mare Tranquillitatis?
~2.9 billion years
Every year, Proxima Centauri, the closest star to the sun, is observed to move 1.5 arcseconds with respect to the background stars for six months, followed by a return to its original position over the course of the next six months. How far away is Proxima Centauri? [diameter of Earth's orbit = 2 AU (astronomical units)]
~280,000AU
On which of the following planets does the crust move across the mantle?
Venus & Earth
Many textbooks misstate this without thinking carefully...so think carefully: Which of Galileo's discoveries is evidence for the heliocentric model?
Venusian phases
Many of the planetesimals that formed in the outer solar nebula
Were ejected into the Oort cloud, when they passed too close to Jupiter or Saturn & Were ejected into the Kuiper belt, when they passed too close to Uranus or Neptune & Remained in the Kuiper belt, where they formed
Which of the following statements is true?
When lunar eclipses occur, the moon is full.
The sun at midday is the lowest in the sky on the:
Winter solstice
You see a total eclipse of the sun. Two Saros cycles later, you find yourself at the same location
You would have to travel far to see another solar eclipse
Select all that apply. It is hotter in summer and colder in winter because:
Your hemisphere of Earth is tipped toward the sun in summer
It is hotter in summer and colder in winter because:
Your hemisphere of Earth is tipped toward the sun in summer and away from the sun in winter
The semi-major axis of a moon's orbit around a planet is 0.0072 AU. The period of its orbit is 0.020 years. What is the planet's mass?
0.00093 solar masses
The Very Large Array (VLA) is a 27-telescope radio interferometer. when spread out over an area 600m in diameter, it resolves 0.06-cm light to
0.004 arcminutes
When at closest approach to Earth, Planet X is observed to be 3.8 arcseconds in diameter. What is Planet X's diameter in meters?
1.2 x 10^8
The room is 300 K. The peak wavelength that it is emitting:
9.7 micro-m
Venus is observed to orbit the sun every 0.62 years. What is the semi-major axis of Venus's orbit in AU?
0.73AU
Number of spacecraft that have visited (flybys count) Uranus and Neptune
1
Atmospheric seeing corresponding to an above-average observing site on an above-average observing night
1 arcsecond
About how hot would the Earth have to get for us to lose the oxygen in our atmosphere to space?
4530 K
A new planet is discovered! Planet X is observed to orbit the sun every 300 years. What is the semi-major axis of Planet X's orbit in AU?
45AU
Not counting Earth's moon, number of large moons that had been discovered by the end of the 17th century
5
What is the mass of Planet X in kilograms and in Earth masses? (The mass of the sun is 2.0 × 1030 kg. The mass of Earth is 6.0 × 1024 kg.)
5.0 x 10^26 kg and 83 Earth masses
How long does it take to send a short message to the New Horizons spacecraft beyond Pluto? New Horizons is currently 6.4 × 109 km away.
5.9 hours
On average, Venus is 0.72 AU from the sun and its surface temperature is 735 K. Calculate how much of this is due to Venus's greenhouse effect? (On average, Venus reflects 75% of incoming light back into space.)
503K
A new planet is discovered in an approximately circular orbit beyond Pluto. It moves at a rate of approximately 1° per year. It's semi-major axis is approximately:
50AU
What is the average density of Planet X?
550 kg/m^3
What is the peak wavelength and observed color of a 50,000 K star?
58nm and blue
The frequency of 500-nm wavelength light:
6 x 10^14 Hz
At perihelion (closest approach to the sun), Mercury is 0.31 AU from the sun. Calculate how hot it gets on Mercury when the sun is directly overhead at perihelion. (On average, Mercury reflects 12% of incoming light back into space.)
684K
A spacecraft orbits Earth in a circular orbit at 3.8 Earth-Moon distances. What is its orbital period?
7.4 lunar months
An object emitting 500-nm wavelength light moves away from you at half of the speed of light. What is the observed wavelength of the light?
750nm
An asteroid passes Earth over its equator. Pictures are taken of it from Earths north and south poles simultaneously. In these pictures, the position of the asteroid differs by 0.75°. How far away was the asteroid from Earth when the pictures were taken?
76 Earth diameters
You watch a bright star rotate 120° around the north celestial pole. How long have you been watching this star?
8 hours
A bright star crosses the meridian at midnight. When will it cross the meridian in 4 months?
8 hours earlier
A star with a surface temperature that is three times that of the sun emits how many times more energy per unit area in a given amount of time?
81
What is the diameter of Planet X in Earth diameters and in AU? (The diameter of Earth is 1.3 × 107 m.)
9.2 Earth diameters and 8.0 x 10^-4 AU
At closest approach, a planet is 2.3 x 10^8 km from Earth and measures 0.85 arcseconds across. How big is this planet in kilometers?
9.5 x 10^2
Select all that apply. Reflecting telescopes are preferred over refracting telescopes because:
A. Light focused with lenses suffers from chromatic aberration. B. Lenses absorb infrared and ultraviolet light. C. Large lenses are heavy and difficult to support. D. Lenses have two surfaces to polish.
At midday on the last equinox, in North Carolina, the sun was:
About 50 degrees above the horizon
Every Saros cycle (19 eclipse years)
All lunar eclipses reoccur
Aliens observe this cloud from a completely different direction. They receive a:
An emission spectrum
Which of the following radio telescopes has the most light-gathering power? (Arecibo, Atacama Large Millimeter Array ALMA, Green Bank Telescope GBT, Very-Large Array VLA)
Arecibo
First to present the heliocentric model of the universe:
Aristarchus
His geocentric model was not very accurate, because it lacked offsets:
Aristotle
You take a spectrum of a star and detect a Balmer absorption series, but all of the wavelengths are shifted toward the red, by 1%. The star is traveling:
Away from you at v = 0.01c
Which of the following statements about the Galilean moons are true?
Because Io is closest to Jupiter, its tidal heating is the greatest, resulting in a mantle of molten rock and consequently in volcanic eruptions and lava flows that are hot enough to have evaporated the surface water, which was lost to space. & Because Europa is farther from Jupiter than Io, its tidal heating is less, resulting in a mantle of solid rock covered by an ocean of water. & Because Ganymede is farther from Jupiter than Europa, its tidal heating is less, resulting in a mantle of solid rock covered by an ocean that probably consists of a slushy mix of water and ice. & Because Callisto is farther from Jupiter than Ganymede, its tidal heating is less, resulting in an interior that was never warm enough to differentiate: It remains an icy/rocky mix.
Why is the sky blue?
Bluer light scatters more than redder light, so sunlight originally not directly toward you, but scattered toward you by atmospheric particles, looks bluer than the sun & For the same reason the sun looks redder at sunrise and sunset
Which of the following moons has the oldest surface? (Io, Europa, Ganymede, Callisto, Enceladus, Triton)
Callisto
Greenhouse gas most responsible for Earth's increasing surface temperature
Carbon dioxide
Earth's average surface temperature has risen by about 1 °F over the past 30 years. The primary cause of this is increasing levels of:
Carbon dioxide in the atmosphere
Light from a star passes through a cloud of hydrogen gas on its way to Earth. If the temperature of the cloud is 1,000 K, we receive a:
Lyman series absorption spectrum
Mercury does not have shield volcanoes, but if it did the largest ones would likely be similar in height to the largest ones on
Mars
Mercury's, Venus's, and Mars's magnetic fields are significantly weaker than Earth's magnetic field. Which of these planets cannot have a liquid metal core?
Mars
Which of the following might be explained by colliding worlds in the early solar system?
Mercury's large metallic core & Venus's slow, backward rotation & Earth's tilted rotation axis and moon & Mar's asymmetric northern and southern hemispheres and Tharsis bulge
Earth, Jupiter, Saturn, Uranus, and Neptune all have strong magnetic fields. To generate a magnetic field, a planet must have a layer that is both fluid, meaning it can move in complex ways, and conductive, meaning that electrons can flow through it easily. To generate a strong magnetic field, this layer, and hence the planet as a whole, must also rotate rapidly (which all of these planets do). Which of the following materials is not responsible for generating any of these planets' magnetic fields?
Molecular hydrogen
Some moons formed around the planet that they orbit while some are wayward asteroids and Kuiper belt objects that were captured gravitationally. The following is a complete list of all of the large and medium-sized moons in the solar system. Which is the second most likely to be a captured world?
Neptune's Nereid
Air is also somewhat viscous. Airplane wings are designed such that when air flows across them they redirect the air downward. This generates lift by which of the following laws:
Newton's Third Law
Consider a planet with a maximum surface temperature of 293K. Will it lose nitrogen gas (molecular weight = 28) in its atmosphere to space if the planet's escape speed is 5.0 km/s?
No
Which of the following is a refracting telescope design?
None of the above (not Prime, Newtonian, Cassegrain, Nasmyth, Coude)
Prior to the Kepler mission, the vast majority of extrasolar planets discovered were Jupiter-like planets in orbits that bring them very close to their parent stars, implying
Stellar systems like our own might be rare, but probably not since our technology was very sensitive to massive planets that pass very close to their parent stars, but much less sensitive to stellar systems like our own. & There might be two classes of stellar systems: ones in which the Jovian planets migrate inward to the inner stellar system and ones in which they do not.
The principal astronomical alignment at Stonehenge, as well as the most common astronomical alignment at archaeoastronomical sites worldwide:
Summer solstice sunrise
Precesses most quickly:
The Earth-Moon system
Which of the following statements about the formation of the Jovian planets cannot be true?
The Jovian planets formed very close to the sun and then migrated out to their current orbits
Select all that apply. From red light through blue light, the solar spectrum exhibits weak hydrogen lines because:
The sun's surface is too cool to collisionally excite many hydrogen atoms to the first excited state, which is necessary for the production of absorption lines at wavelengths that the eye can see. C. The sun's surface is too cool to collisionally excite many hydrogen atoms to the first excited state, which is necessary for the production of Balmer series absorption lines. D. The sun's surface is too cool to collisionally excite many hydrogen atoms beyond the ground state, so mostly absorption lines that the eye cannot see are produced. E. The sun's surface is too cool to collisionally excite many hydrogen atoms beyond the ground state, so mostly Lyman series absorption lines are produced.
Mercury rotates on its axis three times for every two revolutions around the sun, because of
Tidal forces & Mercury's eccentric orbit
(L8, q4)Using these temperatures, calculate if ammonia (NH3) were to leak out of the interior onto the surface of each of these moons, which would be able to retain it as an atmosphere. (The molecular mass of ammonia is 17.)
Titan
Which of the following planets does not have a significant internal source of heat?
Uranus
Which of the following can be explained by colliding worlds in the early solar system?
Uranus's and Neptune's tilted rotation axes & Uranus's moon Miranda's strange surface
Which of the following words likely has the least water?
Venus
In early September, in North Carolina, the day is:
about 12.5 hours long
One person stands at the north pole and one person stands at the south pole. When the moon is directly over the equator, they both take a picture of the moon and the background stars. Afterword, they compare their pictures. Between the pictures, the moon appears to be shifted with respect to the background stars by how many lunar diameters? (diameter of Earth = 12,756 km; circumference = 2π × radius; π = 3.14; distance to moon = 384,400 km; 1 lunar diameter = 0.50°)
~3.8 lunar diameters
Before it collapsed in 1989, Green Bank's 300-foot diameter telescope mapped the sky at 21 cm. What was its resolving power?
~9 arcmin