MSU ISP 205 Final Exam

What do astronomers mean when they say the universe is expanding?

Average distances are increasing between most galaxies.

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

The Greeks rejected the notion that the Earth orbits the Sun. Why?

They could not measure parallax (a change in stars' positions on the sky due to the Earth's orbit)

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.

What is the main reason it is warm in Michigan in the summer?

The tilt of the Earth's axis means we receive the most direct sunlight then.

Consider four planets that are identical except for different tilts of their rotation axis compared to the axis of their orbit around their Sun. One has no tilt at all, another one a tilt of 10 degrees, the third a tilt of 23 degrees, and the fourth a tilt of 45 degrees. Which of these four planets will have the largest seasonal changes in temperature in its northern and southern hemispheres (coldest winters and warmest summers)?

The one with a 45 degree tilt.

When there is a solar eclipse, what is the phase of the moon?

New moon.

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.

If you left a camera out to take time-lapse photographs of the moon for a whole month, would you be able to photograph the Moon's entire surface?

No, half of the Moon is always pointed away from Earth.

You observe a full moon rising at sunset. What will you see 6 hours later?

a full moon on or near your meridian

When we see Venus in its new phase, what phase would Earth be in as seen by a hypothetical Venetian?

full

Which of the following statements about the orbits of the planets is true?

The eight major planets go around the Sun in the same direction and do so all in the same plane like a disk.

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.

Rank the following 4 items by how long it takes for light to reach us from these object, from shortest to longest.
The Andromeda Galaxy
the center of the Milky Way
Pluto
Sun.

Sun, Pluto, center of the Milky Way, the Andromeda Galaxy.

The current best estimate for the age of the universe is about

14 billion years.

Which statement is false?
1. A constellation demarcates a patch of sky, making it easier for astronomers to locate interesting sources.
2. Modern-day constellations include Musca the Fly and Triangulum the Triangle.
3. There are 88 constellations, as defined by the International Astronomical Union.
4. Practically every ancient culture had their own version of constellations, typically used for story telling.

1

Identify the falsifiable statement below:
1. President Kennedy's murder was orchestrated by an undetectable shadow government of the United States.
2. The laws of nature are magnificent and beautiful.
3. The Sun is at the center of the solar system.
4. The universe was created by God.

3

What did Tycho, Kepler, and Newton do?

Tycho collected the data, Kepler provided the model in the form of laws, Newton explained the model in terms of gravity.

Galileo observed all of the following. Which observation offered direct proof of a planet orbiting the Sun?

phases of Venus.

What would change if the Earth started spinning faster?

A day would be shorter.

Suppose the Sun were to shrink suddenly in size while its mass stayed the same. According to the law of conservation of angular momentum, what would happen?

The Sun's rate of rotation would speed up.

Imagine a Star Wars type spaceship in orbit around a planet. Its engine suffers a severe malfunction, and explodes. What is the most physically realistic depiction of this event?

The spacecraft breaks apart, and the pieces continue to orbit the planet.

Conservation of angular momentum dictates that the orbital speed of a planet

is faster when it is closer to the Sun and slower when it is farther away.

How would the gravitational force between Earth and Moon change if the Moon were moved 4 times further away?

The force would be 16 times weaker.

Which planet is moving more slowly around the Sun?

Jupiter

Why are astronauts weightless in the Space Station?

because the Space Station is free falling around the Earth.

The mass of Jupiter can be calculated by measuring...

...the orbital period of one of Jupiter's moons and the distance between Jupiter and that moon.

The surface gravity on the Moon is about 1/6 that of Earth. What is the mass of a 72 kg person on the Moon?

72 kg

The acceleration due to gravity near the surface of the Earth is about 10 m/s2. How fast is a rock falling if it has been falling for 3 seconds?

30 m/s

Light travels at 300,000 km/sec. About how far does light travel in 10 years?

About 10 light-years

"Roses are red, violets are blue ... ". But why is this?

Roses reflect more red light than other wavelengths, violets reflect more blue light than other wavelengths

From lowest energy to highest energy, which of the following correctly orders the different categories of electromagnetic radiation?

radio, infrared, visible light, ultraviolet, X rays, gamma rays

One star is emitting primarily visible light and another star is emitting primarily infrared light. Which star is hotter?

The star emitting visible light.

When you leave class on a sunny day, and see the grass and trees, how does this work?

Some of the sunlight emitted by the Sun reflects off the grass and trees, and enters your eyes.

How do we know what the Sun is made out of?

By identifying the absorption lines in its spectrum.

From laboratory measurements, we know that a particular spectral line formed by hydrogen appears at a wavelength of 486.1 nanometers (nm). The spectrum of a particular star shows the same hydrogen line appearing at a wavelength of 480.0 nm. What can we conclude?

The star is moving toward us.

Why don't we glow in the dark?

People only emit light that is invisible to our eyes.

Why are telescopes with larger diameter mirrors better?

More area for collecting light and
Better angular resolution

Which of the following is NOT an important reason for having telescopes in space?

To place the telescope closer to the stars.

Which of the following statements best explains why the planets orbit in nearly a single plane and in the same direction around the Sun?

The planets formed from a disk of rotating gas.

Why are rocky planets close to the Sun and gas giants farther out?

Because the center of the solar nebula was too hot for hydrogen ices to form.

What is the leading scenario for the formation of the Moon?

It formed from the material ejected in a giant impact.

Why did the solar nebula heat up as it collapsed?

As the cloud shrank, its gravitational potential energy was converted to thermal energy.

Why do asteroids and comets differ in composition?

Asteroids formed inside the frost line, while comets formed outside.

If the freezing point of ices of all types was at a much lower temperature, what change would that imply for the formation of our solar system?

The gas giants would have to form at a larger distance.

Which of the following observations of an extrasolar planet system would be inconsistent with our theory of planet formation?

About half of the planets around a star orbit in one direction, and half in the other direction.

The habitable zone is defined as a region around a star where ...

planets could have liquid water on their surface.

Which of these observations would suggest the presence of a planet orbiting a star?

A slight decrease in the brightness of a star that repeats multiple times with regular periods.

A "hot jupiter" is a gas giant with similar mass to jupiter, but ...

it is much closer to its star making its atmosphere much hotter.

You are looking for extrasolar planets using the Doppler technique. What features are most important for you to measure?

The wavelengths of lines in the spectrum.

What type of extrasolar planet is most easily detected by the Doppler technique?

Jupiter-mass planets close to their sun.

Why is Venus so much hotter than Earth?

Venus has significant amounts of carbon dioxide in its atmosphere.

Which of the following shows evidence for ancient river beds?

Mars.

What is the fundamental reason that Mars has become virtually geologically dead (unlike the Earth which is geologically active)?

Its relatively small mass.

If the polar ice decreases, what would happen, and why?

Warming, because more sunlight is absorbed.

What kind of thermal radiation does the Earth emit?

infrared light

Why does increasing the amount a greenhouse gas increase the temperature of a planet?

Greenhouse gases absorb infrared light.

What is the scientific evidence for human contributions to global climate change?

Climate models show that extra carbon dioxide contributed by humans is enough to match the data.

Why is Mars so much colder than the Earth?

Because Mars has a very thin, diffuse atmosphere.

Why didn't a planet form where the asteroid belt is now located?

Gravitational tugs from Jupiter prevented material from collecting together to form a planet.

In what direction does a comet's tail point?

Away from the Sun.

If impacts that destroy much of life on Earth happen about once every 100 million (100,000,000) years, and your typical human life span is about 100 years, what are your chances of dying from an impact?

One in a million (1,000,000).

How does a major impact in one spot on Earth affect the climate of the entire Earth?

It sends debris into the Earth's atmosphere that blocks sunlight, making the Earth's surface cooler.

Why isn't Pluto considered a major planet anymore?

Because it is one of many small icy rocky dwarf planets in the outer solar system.

Order the interior layers of the Sun from the hottest to the coldest.

core, radiation zone, convection zone, photosphere

Why isn't the Sun shrinking or expanding?

Because gas pressure balances gravity in the Sun.

What is the source of the Sun's energy?

Nuclear fusion.

Which of the following statements is an inference from a model (rather than an observation)?

The Sun's core is gradually turning hydrogen into helium.

When the temperature of the Sun's core goes down, what happens next?

Fusion reactions slow down, core shrinks and heats.

How do we know how old the Sun is?

From ages of solar system meteorites, based on radioactive elements.

Which of the following quantities is equal to the energy per second generated by the Sun's nuclear reactions?

the luminosity of the Sun's photosphere

Which of the following properties of a star can be measured during a single night at the telescope?

apparent brightness

If the distance between us and a star is doubled, with everything else remaining the same, the luminosity

remains the same, but the apparent brightness is decreased by a factor of four.

Which main sequence star has has the lowest mass?

M

Which star is the hottest star?

O

If a star has a mass of 10 solar masses and a luminosity of 10,000 solar luminosities, how long is its lifetime? (The Sun's life time is 10 billion years.)

10 million years

How do we estimate the surface temperature of a star?

By obtaining its spectrum and classifying the spectral type.

Which star cluster is the youngest star cluster? The one where the brightest main sequence stars are ...

O stars

What property is common to all main sequence stars?

All are fusing hydrogen into helium.

Which gas is colder ?

Molecular hydrogen

Why doesn't a brown dwarf become a star? (Choose the best answer.)

It does not have enough mass for its core to start fusion reactions before degeneracy pressure prevents further collapse.

What is the fate of an isolated brown dwarf?

It will remain a brown dwarf forever.

Which of the following sequences correctly describes the stages of life for a low-mass star?

protostar, main-sequence, red giant, white dwarf

What does a massive star ends its life as?

a supernova

Why does the fusion of helium to carbon require a higher temperature and pressure than the fusion of hydrogen to helium?

Because the repulsion of like charges is stronger for the helium nuclei, since they have more protons than the hydrogen nuclei.

Why does the fusion process in a massive star end with iron?

Iron is the most stable element, so energy can't be produced by turning Iron into other elements.

Why do high mass stars have shorter lives than low mass stars?

The CNO cycle is very fast at converting hydrogen to helium.

Why don't low-mass stars have the CNO cycle occurring in their cores?

Their core temperatures are too low.

During which of the following phases of life is a star's pressure and gravity out of equilibrium?

Red giant

When a star runs out of hydrogen in its core, what happens next?

The core shrinks, and hydrogen shell fusion begins.

How will the Sun end its life?

as a white dwarf

Which of the following is closest in size (radius) to a neutron star?

a city

Will our Sun ever undergo a white dwarf supernova explosion? Why or why not?

No, because it is not orbited by another star.

Which of the following objects were first discovered as pulsars?

Neutron star

Which of the following objects are NOT supported by degeneracy pressure?

Black hole

What discovery would contradict current models of a white dwarf?

Discovery of a white dwarf with more than 1.4 solar masses.

Which of the following events does NOT require mass transfer from a companion?

massive star supernova

Which of the following lists objects in the proper order, from smallest to largest?

Neutron Star, Moon, White Dwarf, Sun

Which of the following objects has the largest escape velocity from its surface?

Neutron star with a mass of 1 solar mass

Which of the following objects has the largest escape velocity from a circular orbit with a radius of 0.1 AU?

All of these objects have the same escape velocity