astronomy midterm 2
Planetary orbits are:
fairly circular and in the same plane.
What color does this wavelength correspond to in the visible-light spectrum?
green
How does the Sun's mass compare to Earth's mass? T
he Sun's mass is about 300,000 times the mass of the Earth.
Where should you put a telescope designed for ultraviolet observations?
in Earth orbit
The Hubble Space Telescope obtains higher-resolution images than most ground-based telescopes because it is:
Above earths atmosphere
Compare your answer with the table below and name the planets that orbit just inside and outside Ceres's orbit.
Mars and Jupiter
Why do sunspots appear dark in pictures of the Sun?
They actually are fairly bright, but appear dark against the even brighter background of the surrounding photosphere.
Estimate how much mass the Sun loses through fusion reactions during its 10-billion-year life. You can simplify the problem by assuming the Sun's energy output remains constant.
1.3*10^27kg
Now remember that humans have two eyes that are approximately 7 centimeters apart. Estimate the diffraction limit for human vision, assuming that your "optical interferometer" is just as good as one eyeball as large as the separation of two regular eyeballs.
1.8
How does this compare to the diffraction limit of a 10-meter telescope?
1300
How many Earths could fit inside Jupiter (assuming you could fill up all the volume)? The equation for the volume of a sphere is How many Earths could fit inside Jupiter (assuming you could fill up all the volume)? -
1410
Calculate the diffraction limit of the human eye, assuming a wide-open pupil so that your eye acts like a lens with diameter 0.8 centimeter, for visible light of 500-nanometer wavelength.
16
The light-collecting area of an 8-meter telescope is _____ times that of a 2-meter telescope.
16
Compare the amount of mass lost with Earth's mass.
220
What is the angular separation of the two stars? Give your answer in degrees.
3.6*10^-6
How much greater is the light-collecting area of a 6-meter telescope than a 3-meter telescope?
4 times greater
Use Kepler's third law to find its orbital period.
4.61 years
The Sun will exhaust its nuclear fuel in about __________.
5 billion years
The Sun's average surface (photosphere) temperature is about _____.
5,800 K
What is the Sun's approximate composition (by mass)?
70% hydrogen, 28% helium, 2% other elements
How many Jupiters could fit inside the Sun? The equation for the volume of a sphere is
919
Which of the following is the best answer to the question, "Why does the Sun shine?"
As the Sun was forming, gravitational contraction increased the Sun's temperature until the core become hot enough for nuclear fusion, which ever since has generated the heat that makes the Sun shine.
Which of the following three kinds of objects resides closer to the Sun on average?
Asteroids
Which of the following is not a real difference between asteroids and comets?
Asteroids orbit the Sun, whereas comets just float randomly around in the Oort cloud.
Why do you think the Sun appears white or yellow to our eyes?
Because the Sun radiates in other colors, and because the atmosphere scatter the blue light stronger than the red.
In what way is Venus most similar to Earth?
Both planets are nearly the same size.
The largest terrestrial planet and jovian planet are, respectively:
Earth and Jupiter.
Which of the following best describes why radio telescopes are generally much larger in size than telescopes designed to collect visible light?
Getting an image of the same angular resolution requires a much larger telescope for radio waves than for visible light.
The most abundant ingredient of the Sun and Jupiter is:
Hydrogen.
How is Einstein's famous equation, E = mc2, important in understanding the Sun?
It explains the fact that the Sun generates energy to shine by losing some 4 million tons of mass each day
What do we mean by the diffraction limit of a telescope?
It is the angular resolution the telescope could achieve if nothing besides the size of its light-collecting area affected the quality of its images.
Which of the following best describes what we mean by the focal plane of a telescope?
It is the place where, if we mounted film or an electronic detector, we could get a clear (not blurry) image of an object viewed through the telescope.
In what direction does Uranus orbits the Sun?
It orbits the Sun in the same direction as the other planets.
In the late 1800s, Kelvin and Helmholtz suggested that the Sun stayed hot because of gravitational contraction. What was the major drawback to this idea?
It predicted that the Sun could shine for about 25 million years, but geologists had already found that Earth is much older than this.
Use Wien's law and a sunspot temperature of 4000 =
K to calculate the wavelength of peak thermal emission from a sunspot.- 725 nm
Can the Hubble Space Telescope resolve the two stars?
No
Choose the correct statement describing, what will you see if you look at them with a telescope that has an angular resolution of 0.5 arcsecond. One point of light that is the blurred image of both stars.
Nothing at all.
Which of the following best explains why nuclear fusion requires bringing nuclei extremely close together?
Nuclei normally repel because they are all positively charged and can be made to stick only when brought close enough for the strong force to take hold.
Calculate the density of this planet.
P=8.52g/cm^3
The Sun's visible surface (that is, the surface we can see with our eyes) is called the __________.
Photosphere
How does this color compare with that of the Sun?
Sunspots seem to be dark spots because the surface of the Sun is much brighter.
Based just on the planet's density, would we consider it the largest terrestrial planet or the smallest jovian planet? Why?
Terrestrial planet. Density of more than 5 g/c m 3 g/cm3 requires rocky and metallic composition.
Which of the following is not a major difference between the terrestrial and jovian planets in our solar system?
Terrestrial planets contain large quantities of ice and jovian planets do not.
What do we mean when we say that the Sun is in energy balance?
The amount of energy released by fusion in the Sun's core equals the amount of energy radiated from the Sun's surface into space.
The angular separation of two stars is 0.1 arcseconds and you photograph them with a telescope that has an angular resolution of 1 arcsecond. What will you see?
The photo will seem to show only one star rather than two.
What do we mean when we say that the Sun is in gravitational equilibrium?
There is a balance within the Sun between the outward push of pressure and the inward pull of gravity.
Why are astronomers interested in building observatories capable of detecting neutrinos, cosmic rays, and gravitational waves?
These things are not forms of light, and therefore can provide different types of information than light about objects that emit them.
If the Sun's magnetic field somehow disappeared, there would be no more sunspots on the Sun.
True- because sun spots causes by magnetic fields
Which of the following correctly describes how the process of gravitational contraction can make a star hot?
When a star contracts in size, gravitational potential energy is converted to thermal energy.
Why can't x-ray and gamma-ray telescopes use the same designs as visible-light telescopes?
X-rays and gamma rays have so much energy that they cannot be reflected in the same way as visible light.
The light radiated from the Sun's surface reaches Earth in about 8 minutes, but the energy of that light was released by fusion in the solar core about __________.
a few hundred thousand years ago,helium, energy, and neutrinos.
What is the solar wind?
a stream of charged particles flowing outward from the surface of the Sun
Every second, the Sun converts about 600 million tons of hydrogen into 596 million tons of helium. The remaining 4 million tons of mass is __________.
converted to an amount of energy equal to 4 million tons times the speed of light squared
Compared to the distance between Earth and Mars, the distance between Jupiter and Saturn is ______.
much larger
The source of energy that keeps the Sun shining today is _________.
nuclear fusion
The fundamental nuclear reaction occurring in the core of the Sun is __________.
nuclear fusion of hydrogen into helium
Infrared, and thermal radiation with such peak will be
red-colored.
Estimate how long the Sun would last if it were merely a huge fire that was releasing chemical energy. Assume that the Sun begins with roughly
t= 1.7* 10^4
Which moons of our solar system are sometimes called the Galilean moons?
the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto
The proton-proton chain is __________.
the specific set of nuclear reactions through which the Sun fuses hydrogen into helium
Which pair of photos shows Earth correctly scaled in comparison to the Sun? Which pair of photos shows Earth correctly scaled in comparison to the Sun?-
the sun is huge the earth is tiny
Use Wien's law and the Sun's average surface temperature of about 5800 K to calculate the wavelength of peak thermal emission from the Sun. λ
⊙max �⊙max = 500 nm nm
What is the angular separation of the two stars? Give your answer in arcseconds. θ
� = 1.3×10−2
