Astronomy and Cosmology Midterm Review

Which list of astronomical objects is ordered from smallest to largest?

The solar system; the Milky Way; the Local Group

What is a light-year?

The distance that light travels in one year

Where was most of the material making up Earth and humans formed?

Inside stars that died before Earth formed

Why can't we see a galaxy 15 billion light-years away (assuming a 14-billion-year-old universe)?

Because there has not been enough time since the beginning of the Universe for light to travel that far

If the solar system is scaled down by a factor of 10 billion (Sun as a 14 cm grapefruit), how big is Earth?

The size of a mustard seed

On the 1-to-10-billion scale where the Sun is a grapefruit, how far is it to Alpha Centauri?

across the United States to California (2500 miles)

In winter, where does the Earth's axis point?

The axis still points towards the star Polaris

When does the Sun appear directly overhead (at the zenith) in New Jersey?

Never

How would seasons be affected if Earth's tilt was 40° instead of 23.5°?

The seasons would be more intense (colder winters, hotter summers)

On which date does the Sun get highest in the sky in New Jersey?

June 20, the summer solstice

What was the phase of the moon on August 12, 2026 (total solar eclipse)?

New moon

Which of the following is true about a crescent Moon?

Less than half of the Moon has sunlight falling on it, and it is close to the direction of the Sun

How many arcseconds are in 1 degree?

60 × 60 = 3600 arcseconds

What is the arrow pointing to in standard northern hemisphere local sky diagrams?

Polaris, the north star

How high is Polaris in the sky as viewed from New Jersey (40° north latitude)?

40° above the horizon

If the Sun and a constellation are at the same location in your local sky, that constellation is...

Visible at night from that location at a different time of the year (and part of the zodiac)

What is an accurate statement about the Copernican revolution?

The heliocentric model gives a simpler explanation for retrograde motion of the planets than the geocentric model

What was Kepler's major breakthrough in understanding planetary motion?

He explored elliptical orbits rather than just circular orbits

Which of the following window scenarios could you actually have?

A window on your Moon house that always showed the Earth

Why didn't the ancient Greeks observe stellar parallax?

Stars are so far away that the parallax angle was too small to measure

If the Moon were twice as far from the Earth, the gravitational force attracting it would be...

25% (one-quarter) as strong

Why is Newton's version of Kepler's 3rd Law superior?

Newton derived his version from fundamental laws of motion and gravity, explaining the reasons behind Kepler's empirical observation

The Earth is closest to the Sun in January. Therefore...

The Earth moves fastest around the Sun in January

An asteroid orbits the Sun at an average distance (semimajor axis) of 4 AU. How long does one orbit take?

8 years

If the Sun's gravity magically turned off, what would happen to the Earth?

It would move in a straight line at its current speed and direction

What can we calculate using Europa's orbital period and average distance from Jupiter?

The mass of Jupiter

Which of the following puts parts of the electromagnetic spectrum in correct order from shortest to longest wavelength?

Gamma-ray, X-ray, ultraviolet, visible, infrared, microwave, radio

What does an absorption line spectrum for a star mean?

It is absorbing light at certain wavelengths corresponding to various atomic elements in the star

Approximately what is the highest frequency that you can wave your hand?

4 Hz

Which photon has the most energy among visible, infrared, and radio options?

A green photon from a laser pointer

What can you say about the skin temperature of an alien glowing in the dark visibly?

It is hotter than human skin temperature

What powers the Sun's tremendous luminosity?

Nuclear fusion of hydrogen into helium

Why do sunspots appear darker than their surroundings?

They are cooler than their surroundings

Why does nuclear fusion of hydrogen into helium release energy?

A helium nucleus is lighter than 4 hydrogen nuclei, and the difference in mass is converted to energy by E = mc²

How does the energy generated by nuclear fusion leave the Sun's core?

It is mostly carried away by photons

Which of the following is NOT an advantage of the Hubble Space Telescope over ground-based telescopes?

HST has a larger diameter than all ground-based optical telescopes

Which of the following stars has the highest surface temperature?

Sirius, a blue main-sequence star (spectral type: A)

What information do we need to measure a star's luminosity?

Its apparent brightness and distance

Hydrogen gas at rest emits a spectral line at λ = 656 nm, but we measure λ = 640 nm in a distant star. What can we conclude?

It is moving toward us

Hydrogen gas at rest emits a spectral line at λ = 656 nm, and we measure λ = 656 nm in a distant star. What can we conclude?

It is not moving away from us or toward us

Which of the following is true about the Sun?

Neither A nor B (it does not have the highest luminosity or highest apparent brightness of all visible stars)

How would the apparent brightness of the star Polaris change if it were 2 times closer?

It would be 4 times brighter

Capella has a parallax angle 4 times smaller than Procyon (3.5 parsecs away). What is Capella's distance?

Capella is four times as far away as Procyon

Which of the following stars has the coolest surface temperature?

Betelgeuse, a red supergiant star (spectral type: M)

What stellar quantities are on the axes of a Hertzsprung-Russell diagram?

Surface temperature and luminosity

Which star has the longest main sequence lifetime?

A 0.1 solar mass M star, like Proxima Centauri

The stars in a star cluster are all approximately the same distance from Earth. Which plot is most similar to its H-R diagram?

Apparent brightness (y-axis) vs. color (x-axis)

Why does a 10 solar mass star have a shorter main sequence lifetime than a 1 solar mass star?

The 10 solar mass star has a much higher luminosity

Which of the following stars does not have fusion occurring in the core?

A red giant star, like Aldebaran

Based on H-R diagrams of different star clusters, which cluster is the oldest?

M67

What combination gives the right conditions to form a star out of a molecular cloud?

Low temperature, high density

Why isn't the solar system part of a star cluster today even though the Sun formed alongside other stars?

All of the stars formed moving with different speeds and have moved away

We see a star cluster where stars just like the Sun are starting to leave the main sequence. Approximately how old is it?

10 billion years old

Why does a young star cluster look blue?

The blue stars in young star clusters are more luminous than the red stars

Stars more massive than about 8 solar masses release energy through fusion in their cores all the way up to what element?

Iron

What are Red Giants?

Stars that fuse hydrogen into helium in a shell around the core

After hydrogen is all fused to helium in the core of the Sun, why won't helium start fusing right away?

Fusing helium requires higher temperature due to the stronger electric charge of a helium nucleus

True or False: The Sun's core contains a higher proportion of helium and lower proportion of hydrogen than when born.

True, the Sun is about halfway through its main-sequence lifetime, having fused half its core hydrogen

What happens when a high-mass star has fused to iron in its core?

Core fusion stops because no nuclear reactions of iron can produce energy

If you were to look at our solar system in 15 billion years, what would you see?

A white dwarf

Which of the following objects has the smallest radius?

A 1.3 MSun neutron star

What is the maximum mass limit for a white dwarf set by electron degeneracy pressure (Chandrasekhar limit)?

1.4 MSun

Assuming Sirius A and Sirius B were born at the same time, which star started out more massive?

Sirius B (the white dwarf)

What happens to a white dwarf if it accretes material from a companion and reaches 1.4 MSun?

It explodes as a white dwarf supernova

If the Sun suddenly collapsed to a black hole without changing its mass, what would happen to Earth's orbit?

The Earth would keep orbiting as it currently does

According to General Relativity, what occurs near the event horizon of a black hole?

Time slows down, light is redshifted, and spacetime is curved (all of the above)

If the Sun shrunk down to a few km while keeping its mass, what would happen to the escape velocity from its surface?

It would increase

How does Einstein's General Theory of Relativity describe gravity?

As a distortion of 4-dimensional spacetime

Where do we have strong evidence for the presence of a black hole?

At the center of our Milky Way Galaxy

How do we measure the mass of a black hole in an X-ray binary system?

With the orbital period and velocities inferred from the Doppler shift

What causes Earth's seasons?

Earth's rotation axis is tilted as it orbits the Sun

According to General Relativity, if identical clocks are placed at different distances from a black hole, what does a distant observer measure?

Stronger gravity makes the clock closer to the black hole run slower

What is the correct order of stellar spectral types from coolest to hottest?

M, K, G, F, A, B, O

What keeps a white dwarf stable from collapsing against gravity?

Electron degeneracy pressure

If the distance between two stars decreases by a factor of 3, how does the gravitational force between them change?

Increase by a factor of 9

Where do white dwarfs and supergiants live on the H-R diagram?

White dwarfs bottom left, supergiants top right

White dwarf A (0.8 MSun) and white dwarf B (1.3 MSun) have the same surface temperature. Which is more luminous?

White dwarf A is more luminous (smaller mass means larger radius)

Which Moon phase occurs when the entire side of the Moon facing Earth appears illuminated?

Full Moon

What is true about two stars with different masses regarding their lifespans?

The more massive star will have a shorter lifespan because it fuses its fuel much faster

A white dwarf in a binary system pulls gas from a companion. What happens if its mass grows past 1.4 solar masses?

It explodes as a Type Ia supernova

If you see a full moon tonight, what phase will it be a week later?

Third quarter Moon

Which of these main-sequence stars will have the shortest lifetime?

A blue B star

What process occurs in the core of all main-sequence stars like the Sun?

Fusing hydrogen to helium

Which of the following is true about black holes?

Black holes can be formed as the remnants of massive stars after a supernova explosion

What are two possible end states of a high-mass star after its supernova explosion?

A neutron star or a black hole

What will be the ultimate fate of the Sun?

White dwarf

Which best describes nuclear fusion in stars?

The merging of light atomic nuclei to form heavier ones

As stars move off the main sequence, they typically become...

Cooler and larger

What can we learn from the Doppler effect when observing stars?

It allows us to measure the star's radial velocity (speed towards or away from us)

What is the difference between geocentric and heliocentric models?

Geocentric places Earth at the center, while heliocentric places the Sun at the center

When does a high-mass star stop fusing new elements?

After it has created iron

Which of the following stars has the smallest radius among white dwarfs, neutron stars, main-sequence, and red supergiants?

Scorpius X-1 (a neutron star)

What are the phases of the moon as it goes from new to full?

Waxing crescent, first quarter, waxing gibbous

What happens for an object approaching the event horizon of a black hole from a distant observer's view?

Time slows down

When does the Sun have its lowest path in the sky from New Jersey?

December winter solstice

What is nuclear fusion?

Two or more smaller nuclei slam together to make a larger nucleus

During summer in the southern hemisphere, how would the Sun appear at the South Pole?

The Sun would not set

What will happen when the Sun runs out of hydrogen in its core?

Hydrogen shell fusion will make the Sun a red giant

How do we measure the mass of a star in a binary system?

Newton's version of Kepler's Third Law

Why do we only see the Sun as it was about 8 minutes ago?

Because it takes time for light to travel from the Sun