Astronomy Exam 1
Suppose the Sun suddenly shrunk, reducing its radius by a half (but keeping its mass the same). The force of gravity exerted on Earth by the Sun would ____________.
remain the same
The temperature of the protoplanetary disk allowed
rocks and metals to freeze both in the inner region and outer region, and hydrogen compounds to freeze only in the outer region.
Compared to a cold object, a hotter object of the same size emits most of its light at __________ wavelengths and emits _____ light overall.
shorter, more
If Venus's atmosphere contained the same amount of greenhouse gases as Earth's atmosphere, its surface temperature would be
significantly colder
Ultraviolet light from the Sun is absorbed primarily in Eath's
stratosphere
You discover an asteroid that orbits the Sun with the same 1-year orbital period as Earth. Which of the following statements must be true?
the asteroid's average (semimajor axis) distance from the Sun is 1AU.
A bowling ball and a small marble will fall downward to the surface of the Moon at the same rate because ____________.
the ratio of the force of gravity exerted on an object to the object's mass is the same.
Saturn's rings look bright because __________.
light from the Sun reflects off the material in the rings
Saturn's rings are composed of __________.
lots of individual particles of ice and rock
A kilogram is a measure of an object's ____________.
mass
The Moon takes roughly 28 days to complete one orbit around Earth. If the orbital radius of the Moon were twice its actual value, its orbital period would be
more than 56 days
If a hot gas cloud is moving across the sky (neither towards or away from us), the emission lines would be
neither blueshifted nor redshifted.
In Ptolemy's Earth-centered model, when would Venus appear directly behind the Sun as viewed from Earth?
never
When the Sun dies it will become a white dwarf, which will be roughly the same size as the Earth. Assuming the Sun doesn't lose any mass as it becomes a white dwarf, the force of gravity exerted on Earth due to the Sun will ____________.
not change as the Sun turns into a white dwarf
When you listen to the radio, you are hearing
not radio waves
Suppose you live at a mid-latitude in the Southern Hemisphere (such as in Australia, New Zealand, Chile, or South Africa). When will you have 12 hours of daylight and 12 hours of darkness?
on both the March and September equinoxes
The planets in our solar system are thought to have come from
the same cloud of gas and dust in which the Sun formed.
If the solar nebula initially had no angular momentum,
there would not be any planets orbiting the Sun.
1. We determine Mars's surface temperature from the peak wavelength of the __________ it emits.
thermal radiation
X-rays from the Sun are absorbed primarily in Eath's
thermosphere
If the emission lines in the spectrum of one object are more strongly blueshifted than those from a second object, then the first object is moving
toward us faster than the second object.
On Dec. 21, the Sun is directly above the ____________.
tropic of Capricorn (latitude = 23.5 degrees S)
Convection and weather occur primarily in Eath's
troposphere
The greenhouse effect causes warming primarily in Earth's
troposphere
By only measuring an object's Doppler shift, astronomers tend to
underestimate the object's total speed
. The color of Mars in our sky is determined by the _________ of Mars's spectrum.
visible portion
If the Earth were tilted 90 degrees (rather than 23.5 degrees), summer in the Arctic would be ____________ summer in Colorado.
warmer than
An astronomer looks at the Andromeda galaxy (the other large galaxy in the Local Group) through her telescope. How long ago did that light leave Andromeda?
2.5 million years
Light emitted by our Sun takes roughly:______ to reach the Andromeda galaxy.
2.5 million years
Light emitted by our Sun takes roughly:______ to reach the nearest star
4 years
Light emitted by our Sun takes roughly:______ to reach Pluto
5 hours
Light emitted by our Sun takes roughly: ______ to reach earth
8 minutes
What is the basic reason that we have seasons on Earth?
Earth's axis is tilted relative to the ecliptic plane.
What do you think is the main cause of seasons on Earth?
Earth's tilt brings either the Northern or the Southern Hemisphere closer to the Sun as the Earth orbits.
Which sequence is correctly ordered from smallest to largest?
Earth, Moon's orbit, the Sun, Neptune's orbit
Imagine that you visit an alien world that has an atmospheric composition similar to that of Earth (that is, mostly nitrogen and oxygen) and a surface atmospheric pressure of 1.2 bars. Which of the following statements best describes the effects of this pressure?
It will feel quite similar to the atmospheric pressure on Earth.
Imagine being on the Moon and looking at the thermal radiation spectrum of Earth. How would it compare to the spectra shown on the graph in the video?
It would be very similar to the spectrum of the human.
Why does Mars appear reddish in color?
It reflects most of the Sun's red light while absorbing most of its blue light.
What happens to Earth's axis as we orbit around the Sun over the course of each year?
It remains pointed in the same direction at all times.
What is special about the June solstice?
It's the day on which the Northern Hemisphere receives its most direct sunlight
Which of the following properties do you think we can infer simply by looking at the spectrum of a star or of a planet's atmosphere?
Its temperature Its chemical composition
As a comet orbits around the Sun, its maximum speed is twice its minimum speed. What can we say about its orbit?
The comet is twice as far from the Sun at aphelion as at perihelion.
Suppose that Mars had a higher surface temperature. How would its spectrum be different?
The peak in the infrared would be at shorter wavelength
What factor determines how long it takes a planet to complete one orbit around the Sun (the orbital period)?
The planet's average distance from the sun.
If you stood on a planet with four times the mass of Earth, and twice Earth's radius, how much would you weigh?
The same as on Earth.
How do you think a traditional radar gun is able to determine the speed of a moving car?
The speed of the car is determined from how much the wavelength of the returning radar beam changes.
Carbon dioxide in Mars's atmosphere produces _____________ in the infrared portion of its spectrum.
absorption lines
Light received from a galaxy at the far end of the Local Supercluster was emitted roughly ____________.
10^8 years ago
What is the main reason Venus is much hotter than Earth?
Venus has a thick atmosphere of carbon dioxide.
All of the following statements are true. Which one can be explained by Kepler's third law?
Venus orbits the Sun at a faster orbital speed than Earth.
Which of the following can you observe about Venus with the naked eye?
Venus sometimes shines brightly in the eastern sky shortly before dawn Venus sometimes shines brightly in the western sky shortly after sunset
When is the Sun highest in the sky at noon for people living in Sydney, Australia?
Winter solstice (Dec. 21)
If a hot gas cloud is moving toward us, the frequency of the emission lines will be
higher than those of a stationary gas cloud.
The inner planets are small and rocky and the outer planets are mostly large and gaseous because
hydrogen compounds are more abundant than rocks and metals so that beyond the frost line the gravity of large ice planetesimals could capture the abundant light gases.
What kind of light do greenhouse gases absorb and transmit?
infrared light and transmit visible light
As the solar nebula collapsed under its own gravity,
it heated up and spun up.
What would the temperature of a planet be if its reflectivity were 1.0?
it would be very, very cold
Mars's surface temperature would be higher if
its atmosphere contained more greenhouse gases
Thermal radiation gets its name because __________.
its spectrum depends on the temperature of the object emitting it
A planet is discovered orbiting the star 51 Peg with a period of four days (0.01 years). 51 Peg has the same mass as the Sun. Mercury's orbital period is 0.24 years, and Venus's is 0.62 years. The average orbital radius of this planet is
less than Mercury's.
Which object emits more infrared radiation?
A star that is the same size as the Sun but five times hotter
Why do the planets orbit the Sun (i.e. why don't they crash into the Sun)?
Although the planets experience a force of gravity from the Sun, since they are moving, their trajectories bend around the Sun rather than lead directly into the Sun.
Why do we essentially see the same face of the Moon at all times?
Because the Moon's rotational and orbital periods are equal.
Earth is slightly closer to the Sun in January than in July. How does the area swept out by Earth's orbit around the Sun during the 31 days of January compare to the area swept out during the 31 days of July?
Both areas are the same
Suppose two comets, comet A and comet B, were orbiting the Sun, having the same average orbital radii. If comet A had a higher eccentricity than comet B, which comet would, during some portion of its orbit, have the highest orbital speed?
Comet A
Earth is made mostly of rocky material and metals such as iron, whereas Jupiter is mostly hydrogen and helium. What is the main reason that Earth's composition is different from Jupiter's?
Compared to Jupiter, Earth formed in a hotter region, where only rocks and metals could exist as solids.
Roughly what time of day is a Third Quarter Moon highest in the sky?
Dawn
The _______________ allows us to determine how fast Mars is moving toward or away from us.
Doppler effect
Suppose the moon's orbital position is located as shown in the figure below. At what time will the moon be highest in the sky?
Dusk
For the radial speed of an astronomical object to be determined, what must the object's spectrum contain?
Either absorption or emission lines
When is the Sun in the Northern part of the sky at noon for people who live on the equator?
From March 21 until Sep. 21
On your way to work about two hours after sunrise, you notice the moon setting. What phase is it in?
Gibbous
What is the reason we see phases of the Moon?
Half the Moon is always illuminated by the Sun, but the phase we see depends on how much of this half we are looking at from Earth
Incandescent light bulbs emit thermal radiation because their filaments are heated to about 2500 Kelvin. LED light bulbs emit only at particular visible wavelengths. Why do incandescent bulbs require more energy to shine with the same amount of visible light as LED bulbs?
Incandescent bulbs emit most of their energy as infrared light.
Why doesn't Mars have a stratosphere?
It lacks a layer of ultraviolet absorbing gas.
If an astronomer claims to have discovered an object with a very eccentric orbit, which of the following best describes the orbital trajectory of the object?
It looks like a very squashed oval
The earliest radio broadcasts on Earth were emitted about 100 years ago. Approximately where are these initial radio waves now? (Radio waves are a type of radiation, so they travel at the speed of light)
Just passing relatively local stars in our galaxy
What can be explained by Kepler's second law?
Mars moves faster in its orbit when it is closer to the Sun than when it is farther from the Sun.
What is the main reason Mercury is much hotter than the Moon?
Mercury is closer to the sun
uppose object A has three times as the mass of object B. Identical forces are exerted on the two objects. Which statement is true?
The acceleration of object B is three times that of object A.
Which of the following statements correctly describes the motion of the particles in Saturn's rings?
Particles in the inner rings orbit Saturn at a faster speed than particles in the outer rings
Two planets are observed going around a star. Planet Xoron has an orbital period that is twice as long as planet Krypton. Which planet has a shorter average orbital radius?
Planet Krypton
For people in Australia, the first day of spring is approximately ____________.
September 21st
Suppose you go outside and look at three stars. Star A is blue, Star B is white, and Star C is red. Which star is the hottest and which star is the coldest?
Star A is the hottest and Star C is the coldest.
What is true about summer compared to winter
Temperatures tend to be warmer in summer. The Sun follows a longer and higher path through your sky in summer. You have more daylight and less darkness in summer
What is the cause of the lunar phases (i.e. why doesn't the Moon look the same every day)?
The Moon's orbit around Earth causes different amounts of the illuminated side of the Moon to be visible from Earth.
Consider a planet orbiting another star that is very similar to our Sun. Assume the planet is about the size of Earth and has an Earth-like orbit around its star. Which of the following statements are true about the light coming from the star and planet?
The star emits much more total light than the planet. The planet emits virtually all its light as infrared light. The star's spectrum peaks in visible light.
Suppose a parachutist is falling toward the ground, and the downward force of gravity is exactly equal to the upward force of air resistance. Which statement is true?
The velocity of the parachutist is not changing with time.
If a star is moving away from you at a constant speed, how do the wavelengths of the absorption lines change as the star gets farther and farther?
The wavelengths remain the same.
Do you think Northern Hemisphere summers are warmer or colder than Southern Hemisphere summers on Mars?
They are colder
Do you think Northern Hemisphere winters are warmer or colder than Southern Hemisphere winters on Mars?
They are warmer
Two observers, one in northern Canada and the other in Australia, are looking at the Moon on the same day. The observer in Canada sees a Third Quarter Moon. What does the observer in Australia see?
Third Quarter Moon
If a star is moving away from you at constant speed, the absorption lines in its spectrum will
be redshifted (have wavelengths longer than those of an identical stationary star).
Suppose the solar nebula had been too warm for ices to condense anywhere. If a planet had still formed at Jupiter's location, it most likely would have
been similar in composition to Earth, with a much smaller mass than the real Jupiter.
Which of the following gases are greenhouse gases?
carbon dioxide and water
If the Earth did not have a tilt, the weather during June in Colorado would be ____________.
colder
If the Earth were tilted 45 degrees (rather than 23.5 degrees), winters in Colorado would be ____________.
colder
As the solar nebula collapsed, it became a disk because
collisions between particles made the particles go in more-or-less the same direction
Hot gas in Mars's upper atmosphere produces ________________in the ultraviolet portion of its spectrum.
emission lines
The "edge of space" occurs in the layer we call the
exosphere
By how many orders of magnitude is the distance to the nearest stars greater than the orbital radius of Neptune?
four
which Venus phase would be impossible to see (from Earth) if Venus orbited Earth as described in Ptolemy's Earth-centered model?
gibbous (nearly full)
Suppose the solar nebula had cooled much more before the solar wind cleared away the remaining gas. In that case, the terrestrial planets likely would have ended up
with a higher abundance of hydrogen compounds and larger size
If Earth's orbit were very eccentric, but the average distance from the Sun were still 1 AU, its orbital period
would still be one year.
