Astronomy Midterm

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Which of the following statements about electrical charge is true?

A positive charge and a negative charge will attract each other.

A gas heated to millions of degrees would emit

Mostly x rays.

Suppose you are listening to a radio station that broadcasts at a frequency of 97 Mhz (megahertz). Which of the following statements is true?

The radio waves from the radio station are causing electrons in your radio's antenna to move up and down 97 million times each second.

Laboratory measurements show hydrogen produces a spectral line at a wavelengh 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.

Betelgeuse is the bright red star representing the left shoulder of the constellation Orion. All of following statements about Betelgeuse are true. Which one can you infer from its red color?

It's surface is cooler than the surface of the sun.

Suppose you look at a spectrum of visible light by looking through a prism or diffraction grating. How can you decide whether it is an emission line spectrum or an absorption line spectrum?

An emission line spectrum consists of bright lines on a dark background, while an absorption line spectrum consists of dark lines on a rainbow background.

Visible light from a distant star can be spread into a spectrum by using a glass prism or

A diffraction grating.

Suppose you see two stars: a blue star and a red star. Which of the following can you conclude about the two stars? Assume that no Doppler shifts are involved. (Hint: Think about the laws of thermal radiation).

The blue star has a hotter surface temperature than the red star.

Suppose you want to know the chemical composition of a distant star which piece of information is most useful to you?

The wavelengths of spectral lines in the star's spectrum.

What is the name given to 2H?

Deuterium

An atom of the element iron has an atomic number of 26 and an atomic weight of 56. If it is neutral, how many protons, neutrons, and electrons does it have?

26 protons, 30 neutrons, 26 electrons

When an electron in an atom goes from a higher energy state to a lower energy state, the atom

emits a photon of a specific frequency.

Compared to the volume of tis nucleus, the volume of an atom is about

a trillion times greater.

Which of the following statements about thermal radiation is always true

A hot object emits more total radiation per unit surface area than a cool object.

The spectra of most galaxies show redshifts. This means that their spectral lines

Have wavelengths that are longer than normal

If we observe one edge of a planet to be redshifted and the opposite edge to be blueshifted, what can conclude about the planet

The planet is rotating.

Which of the following statements about thermal radiation is always true

A hot object emits photons with a higher average energy than a cool object.

Everything looks red through a red filter because

The filter transmits red light and absorbs other colors.

If we observe one edge of a planet to be redshifted and the opposite edge to be blueshifted, what can we conclude about the planet

The planet is rotating.

The planet neptune is blue in color. How would you expect the spectrum of visible light from Neptune to be different from the visible-light spectrum of the sun

The two spectra would have similar shapes, except Neptune's spectrum would be missing a big chunk of the red light that is present in the sun's spectrum.

If a material is highly opaque, then it

absorbs most light.

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.

Sublimation is the process in which

molecules go from the solid phase to the gas phase.

We can learn a lot about the properties of a star by studying its spectrum. All of the following statements are true except one. Which one?

The total amount of light in the spectrum tells us the star's radius.

From the 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 best describes the principle advantage of CCDs over photographic film?

CCDs capture a much higher percentage of the incoming photons than film.

What do we mean by the diffraction limit of a telescope?

It is the best angular resolution the telescope could achieve with perfect optical quality and in the absence of atmospheric distortion.

Which of the following is not an advantage of the Hubble Space telescope over ground-based telescopes?

It is closer to the stars.

Suppose you point your telescope at a distant object. Which of the following is not an advantage of taking a photograph of the object through the telescope as compared to just looking at the object through the telescope.

The photograph will have far better angular resolution than you can see with your eye.

What does the technique of interferometry allow?

It allows two or more telescopes to obtain the angular resolution of a single telescope much larger than any of the individual telescopes.

What is a CCD?

It is an electric detector that can be used in place of photographic film for making images.

Which of the following statements about light focusing is not true?

The focal plane of a reflecting telescope is always located within a few inches of the primary mirror.

What is the angular resolution of the human eye?

about 1 arcminute, or 1/60 of a degree.

In what wavelength range was interferometry first routinely used.

radio.

What is the purpose of adaptive optics?

It reduces blurring caused by atmospheric turbulence for telescopes on the ground.

Which of the following studies is best suited to astronomical observations that fall into the category called timing?

Studying how a star's brightness varies over a period of 3 years.

Which of the following statements best describes the two principal advantages of telescopes over eyes?

Telescopes can collect far more light with far better angular resolution.

Telescopes operating at this wavelength must be cooled to observe faint astronomical objects.

extreme infrared.

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.

Which of the following is not a reason why telescopes tend to be built on mountaintops that are relatively far from cities and are in regions with dry climates?

The thin air on mountaintops makes the glass in telescope mirrors less susceptible to warping.

What is an artificial star?

A point of light in Earth's atmosphere created by a laser for the purpose of monitoring atmospheric fluctuations.

How does the light-collecting area of an 8-meter telescope compare to that of a 2-meter telescope?

The 8-meter telescope has 16 times the light-collecting area of the 2-meter telescope.

What does angular resolution measure?

The angular size of the smallest features that the telescope can see.

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.

Which planet listed below has the most extreme seasons?

Uranus.

Venus has a higher average surface temperature than Mercury. Why?

Because its surface is heated by an extreme green house effect.

Why was it advantageous for the voyager mission to consist of flybys rather than orbiters.

Each individual spacecraft was able to visit more than one planet.

Which of the following is not a real difference between asteroids and comets.

Asteroids orbit the Sun while comets just float randomly around in the Oort cloud.

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.

The planet in our solar system with the highest average surface temperature is

Venus.

Which of the following statements about Pluto is not true?

It is the largest known object that is considered to be a dwarf planet.

In what way is pluto more like a comet than a planet?

It is made mostly of rock and ice.

The most metal-rich terrestrial planet is

Mercury.

What is the Oort cloud?

It is not really a cloud at all, but rather refers to the trillion or so comets thought to orbit the sun at great distances.

Mars has two moons that are most similar in character to

small asteroids.

Which of the following is furthest from the sun?

A comet in the Oort cloud.

Compared to the distance between Earth and Mars, the distance between Jupiter and Saturn is

much larger.

Which of the following puzzles in the solar system cannot be explained by a giant impact event?

The orbit of Triton in the opposite direction to Neptune's rotation.

Suppose you find a rock that contains some potassium-40 (half-life of 1.3 billion years). You measure the amount and determine that there are 5 grams of potassium-40 in the rock. By measuring the amount of its decay product (argon-40) present in the rock, you realize that there must have been 40 grams of potassium-40 when the rock solidified. How old is the rock?

3.9 Billion years.

According to our theory of solar system formation, why do all the planets orbit the Sun in the same direction and in nearly the same plane?

The laws of conservation energy and conservation of angular momentum ensure that any rotating, collapsing cloud will end up as a spinning disk.

According to our present theory of solar system formation, why were solid planetesimals able to grow larger in the outer solar system than in the inner solar system?

Because only metal and rock could condense in the inner solar system, while ice also condensed in the outer solar system.

According to our present theory of solar system formation, which of the following lists the major ingredients of the solar nebula in order from the most abundant to the least abundant?

hydrogen and helium gas; hydrogen compounds; rock; metal.

What is the primary reason that astronomers suspect that some jovian moons were captured into their current orbits?

Some moons have orbits that are "backwards" (compared to their planet's rotation) or highly inclined to their planet's equator.

The terrestrial planets are made almost entirely of elements heavier than hydrogen and helium. According to modern science, where did these elements come from?

They were produced by stars that lived and died before our solar system was born.

According to our theory of solar system formation, what is pluto?

Pluto is a large Kuiper-belt comet.

Which of the following are relatively unchanged fragments from the early period of planet building in the solar system.

Oort cloud comets, the moons of mars, asteroids, kuiper belt comets (all of the above).

What happened during accretion phase of the early solar system?

Particles grew by colliding and sticking together.

Which of the following statements about electrons is not true.

Electrons orbit the nucleus rather like planets orbiting the sun.

Which of the following statements is true of green grass.

It absorbs red light and reflects green light.

consider an atom of gold in which the nucleus contains 79 protons and 118 neutrons. What is its atomic number and atomic weight?

The atomic number is 79, and the atomic weight is 197.

You observe a distant galaxy. You find that a spectral line of hydrogen that is shifted from its normal location in the visible part of the spectrum into the infrared part of the spectrum. What can you conclude?

The galaxy is moving away from you.

Consider an atom of carbon in which the nucleus contains 6 protons and 7 neutrons. What is its atomic number and atomic mass number.

atomic number=6;atomic mass number=13

Which of the following statements about x rays and radio waves is not true?

X rays travel through space faster than radio waves.

Suppose that Star X and Star Y both have redshifts, but Star X has a larger redshift than Star Y. What can you conclude?

Star X is moving away from us faster than Star Y.

A perfectly opaque object that absorbs all radiation and reemits the absorbed energy as thermal radiation is

a thermal emmiter.

The angular seperation 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.

Which of following effects is caused by atmospheric turbulence.

twinkling of stars.

Suppose you have two small photographs of the Moon. Although both look the same at small size, when you blow them up to poster size one of them still looks sharp while the other one becomes fuzzy (grainy) looking. Which of the following statements is true?

The one that still looks sharp at large size better (smaller) angular resolution than the one that looks fuzzy.

Which of the following wavelength regions cannot be studied with telescopes on the ground?

both B and C.

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.

What is the purpose of adaptive optics?

to eliminate the distorting effects of atmospheric turbulence for telescopes on the ground.

The terrestrial planets in our solar system are

Jupiter, Saturn, Uranus, and Neptune.

Which of the following statements about the recently-discovered object Eris is not true?

It is thought to be the first example of a new class of object.

Which jovian planet does not have rings?

All of the jovian planets have rings.

What is the primary reason why a Pluto flyby mission would be cheaper than a Pluto orbiter?

The fuel needed for an orbiter to slow down when it reaches Pluto adds a lot of weight to the spacecraft.

How do scientists determine the age of the solar system.

radiometric dating of meteorites.

Why did the solar nebula heat up as it collapsed?

As the cloud shrank, its gravitational potential energy was converted to kinetic energy and then into thermal energy.

According to our theory of solar system formation, why does the Sun rotate slowly today?

The Sun once rotated much faster, but it transferred angular momentum to charged particles caught in its magnetic field and then blew the particles away with its strong solar wind.

At extremely high temperatures (million of degrees), which of the following best describes the phase of matter?

a plasma consisting of positively charged ions and free electrons.

All of the following statements about the Sun's corona are true. Which one explains why it is a source of X rays?

The temperature of the corona's gas is some 1 to 2 million Kelvin.

Suppose you watch a leaf bobbing up and down as ripples pass it by in a pond. You notice that it does two full up and down bobs each second. Which statement is true of ripples on the pond.

They have a frequency of 2 hertz.

In what part of the electromagnetic spectrum do the biggest telescopes on Earth operate.

Radio.

Which of the following could not be measured by an observation that uses only imaging.

the rate at which a variable star brightens and dims.

The planet closest in size to Earth is

Venus.

What kind of material in the solar nebula could remain sold at temperature as high as 1,500 K, such as existed in the inner regions of the nebula.

Metals.

What is a compound?

a molecule containing two or more elements.

What do we mean by the diffraction 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.

Consider the following statement: "Rocky asteroids are found primarily in the asteroid belt and kuiper belt while icy comets are found primarily in the Oort cloud. "what's wrong with this statement?"

The Kuiper belt contains icy comets, not rocky asteroids.

At first, the sun's present-day rotation seems to contradict the prediction of the nebular theory because

the theory predicts that the Sun should have been rotating fast when it formed, but the actual rotation is fairly slow.

How much electrical charge does an atom with 6 protons, 6 neutrons, and 5 electrons have?

A positive charge of +1.

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