Astro Midterm 1

Astro Midterm 1

Which of the following observational techniques is most appropriate for measuring Doppler shifts?
Spectroscopy (taking a spectrum)
One of the absorption lines of hydrogen has a rest wavelength of 656 nm (at rest means with respect to the observer, like in a lab). You observe several stars and measure the wavelength of this same hydrogen absorption line in each star. Based on the measured wavelength of this line, which star is moving towards the Earth the fastest?
630 nm
Which of the following statements about X-rays and radio waves is not true?
X-rays travel through space faster than radio waves
Suppose you built a scale-model atom in which the nucleus is the size of a tennis ball. About how far would the cloud of electrons extend?
Several kilometers
Which of the following conditions lead you to see an absorption line spectrum from a cloud of gas in interstellar space?
The cloud is cool and lies between you and a hot star
Betelgeuse is the bright red star representing the left shoulder of the constellation Orion. All the following statements about Betelgeuse are true. Which one can you infer from its red color?
Its surface is cooler than the surface of the Sun
Laboratory measurements show hydrogen produces a spectral line at a wavelength of 486.1 nanometers (nm). A particular star’s spectrum shows the same hydrogen line at a wavelength of 486.0 nm. What can we conclude?
The star is moving toward us
Studying a spectrum from a star can tell us a lot. All of the following statements are true except one. Which statement is not true?
The total amount of light in the spectrum tells us the star’s radius
Which of the following is not an advantage of the Hubble Space Telescope over ground-based telescopes?
It is closer to the stars
From shortest to longest wavelength, which of the following correctly orders the different categories of electromagnetic radiation?
Gamma rays, X-rays, ultraviolet, visible light, infrared, radio
Which of the following is always true about images captured with X-ray telescopes?
They are always shown with colors that are not the true colors of the objects that were photographed
The spectra of most galaxies show redshifts. This means that their spectral lines ________.
have wavelengths that are longer than normal
What is the purpose of adaptive optics?
It reduces blurring caused by atmospheric turbulence for telescopes on the ground
What is the purpose of interferometry?
It allows two or more small telescopes to achieve the angular resolution of a much larger telescope
Why do astronomers need different telescope designs to observe across the electromagnetic spectrum?
Photons of different energy behave differently and require different collection strategies
Why are astronauts weightless in the Space Station?
Because the Space Station is constantly in free-fall around the Earth
Suppose that the Sun shrank in size but that its mass remained the same. What would happen to the orbit of the Earth?
Earth’s orbit would be unaffected
Imagine another solar system, with a star more massive than the Sun. Suppose a planet with the same mass as Earth orbits at a distance of 1 AU from the star. How would the planet’s year (orbital period) compare to Earth’s year?
The planet’s year would be shorter than Earth’s
Which of the following best describes the origin of ocean tides on Earth?
Tides are caused by the difference in the force of gravity exerted by the Moon across the sphere of the Earth
At which lunar phase(s) are tides most pronounced (for example, the highest high tides)?
New and Full moons
Which of the following best explains why the Moon’s orbital period and rotation period are the same?
The Moon once rotated faster, but tidal friction slowed the rotation period until it matched the orbital period
The astronauts feel weightless in the International Space Station, which orbits the Earth once every 90 minutes. Why?
Because they are falling around the Earth
Consider the elliptical orbit of a comet around the Sun. Where in its orbit is the comet moving the fastest?
when it is closest to the Sun
The Moon is constantly falling toward Earth.
True
Consider the statement “There’s no gravity in space.” This statement is:
Completely false
If the Moon were closer to Earth, high tides would:
be higher than they are now
Approximately where is it currently high tide on Earth?
On the portion of Earth facing directly toward the Moon and on the portion of Earth facing directly away from the Moon
How did the Ptolemaic model explain the apparent retrograde motion of the planets?
The planets moved along small circles that moved on larger circles around the Earth.
When Copernicus first created his Sun-centered model of the universe, it did not lead to substantially better predictions of planetary positions than the Ptolemaic model. Why not?
Copernicus used perfect circles for the orbits of the planets.
Earth is farthest from the Sun in July and closest to the Sun in January. During which Northern Hemisphere season is Earth moving fastest in its orbit?
Winter
According to Kepler’s third law (p2 = a3), how does a planet’s mass affect its orbit around the Sun?
A planet’s mass has no effect on its orbit around the Sun
All the following statements are true. Which one follows directly from Kepler’s third law (p2 = a3)?
Venus orbits the Sun at a slower average speed than Mercury
Galileo challenged the idea that objects in the heavens were perfect by ________.
observing sunspots on the Sun and mountains on the Moon
Galileo observed all of the following. Which observation offered direct proof of a planet orbiting the Sun?
Phases of Venus
Which of the following is not consistent with the major hallmarks of science?
Science consists of proven theories that are understood to be true explanations of reality.
Which of the following is not part of a good scientific theory?
A scientific theory cannot be accepted until it has been proven true beyond all doubt
Imagine for a moment that despite all the evidence, Earth actually is not rotating and orbiting the Sun. Which of these hypothetical observations (none of them are real) would be inconsistent with our Sun-centered view of the solar system?
We discover a small planet beyond Saturn that rises in the west and sets in the east each day
What do we mean by a geocentric model of the universe?
A model designed to explain what we see in the sky while having the Earth located in the center of the universe
What was the Ptolemaic model?
An Earth-centered model of planetary motion published by Ptolemy
The great contribution of Nicholas Copernicus was to ________.
create a detailed model of our solar system with the Sun rather than Earth at the center
The great contribution of Tycho Brahe was to ________.
observe planetary positions with sufficient accuracy so that Kepler could later use the data to discover the laws of planetary motion
Which of the following was not observed by Galileo?
Stellar parallax
Which of the following is not one of, nor a direct consequence of, Kepler’s Laws?
The force of attraction between any two objects decreases with the square of the distance between their centers.
Which of the following statements about scientific models is true?
A model can be used to explain and predict real phenomena
How did Eratosthenes estimate the size of Earth in 240 B.C.?
by comparing the maximum altitude of the Sun in two cities at different latitudes
Why did Ptolemy have the planets orbiting Earth on “circles upon circles” in his model of the universe?
to explain the fact that planets sometimes appear to move westward, rather than eastward, relative to the stars in our sky
The Andromeda Galaxy is faintly visible to the naked eye in the constellation Andromeda. Suppose instead it were located in the same direction in space as the center of the Milky Way Galaxy (but still at its current distance). How would it appear to the eye in that case?
We could not see it at all
When traveling north from the United States into Canada, you’ll see the North Star (Polaris) getting ________.
higher in the sky
Suppose you are facing north and you see the Big Dipper close to your northern horizon, with Polaris (and the Little Dipper) above it. Where will you see the Big Dipper in six hours?
To the right of Polaris; that is, 90 degrees counterclockwise from its current position
In any particular place on Earth, certain constellations are visible in the evening only at certain times of the year because ________.
our evening view of space depends on where Earth is located in its orbit around the Sun
The Sun’s path, as viewed from the equator, is highest in the sky on ________.
the spring and fall equinoxes
Suppose Earth’s axis tilt was significantly greater than its current 23.5 degrees, but Earth’s rotation period and orbital period were unchanged. Which statement below would not be true?
The length of each season (for example, the number of days from the summer solstice to the fall equinox) would be significantly longer than it is now.
How does Earth’s varying distance from the Sun affect our seasons?
It doesn’t — Earth’s orbital distance plays no significant role in the seasons.
Suppose you live in the United States and you see a crescent moon in your evening sky tonight. What will a friend in South America see tonight?
Your friend will also see a crescent moon
Suppose it is full moon. What phase of Earth would someone on the Moon see at this time?
New Earth
You observe a full moon rising at sunset. What will you see at midnight?
A full moon high in the sky
All the following statements are true. Which one explains the reason that there is not a solar eclipse at every new moon?
The orbital plane of the Moon is tilted slightly (by about 5 degrees) to the ecliptic plane.
For most of history, the lack of observable stellar parallax was interpreted to mean that ________.
Earth is stationary at the center of the universe
During the period each year when we see Mars undergoing apparent retrograde motion in our sky, what is really going on in space?
Earth is catching up with and passing by Mars in their respective orbits.
Suppose you see a photo showing Jupiter half in sunlight and half in shadow (that is, a first quarter Jupiter). This photo might have been taken by ________.
the Galileo spacecraft that orbited Jupiter in the 1990s
What is the ecliptic?
The path the Sun appears to trace around the celestial sphere each year
If you are located in the Northern Hemisphere, which of the following correctly describes a relationship between the sky and your location?
The altitude of the north celestial pole equals your latitude.
Each choice below describes how a few astronomical phenomena are related to time periods. Which list is entirely correct? (Careful: some lists are partially correct.)
Earth’s rotation defines a day.
The cycle of the Moon’s phases takes about a month.
Earth’s orbit defines a year.
Earth’s cycle of axis precession takes 26,000 years.
If we have a new moon today, when we will have the next full moon?
in about 2 weeks
We cannot see a new moon in our sky because ________.
a new moon is quite near the Sun in the sky
Lunar eclipses can occur only during a ________.
full moon
During the time that a planet is in its period of apparent retrograde motion: ________.
Over many days or weeks, the planet moves westward relative to the stars, rather than the usual eastward relative to the stars
When we look at an object that is 1,000 light-years away we see it ________.
as it was 1,000 years ago
Suppose we look at two distant galaxies: Galaxy 1 is twice as far away as Galaxy 2. In that case ________.
we are seeing Galaxy 1 as it looked at an earlier time in the history of the universe than Galaxy 2
Suppose we make a scale model of our solar system, with the Sun the size of a grapefruit. Which of the following best describes what the planets would look like?
The planets are all much smaller than the Sun. Four planets are within about 20 meters of the Sun, while the rest planets are spread much farther apart.
Why do the patterns of the stars in our sky look the same from year to year?
Because the stars in the constellations are so far away
Which of the following is not a general difference between a planet and a star?
All planets are made of rock and all stars are made of gas
Place the following items in order of actual physical size, from smallest to largest.
Planet, star, solar system, galaxy
Rank the following 4 items by how long it takes for light to reach us from these objects, from shortest to longest.
Sun, Pluto, center of the Milky Way, the Andromeda Galaxy
Rank the following 3 items from nearest to farthest. Hint: the Orion Nebula is a cloud of gas in which young stars are being born within the Milky Way, about 1500 light-years away.
Alpha Centauri, Orion Nebula, star in the center of the Milky Way