Astronomy Homework Review

What was the phase of the moon on the total solar eclipse of April 8, 2024?

new moon

In the first direct detection of gravitational waves by LIGO in 2015, where did the waves come from?

the merger of two black holes

Why do we think there is a supermassive black hole at the center of our Milky Way Galaxy?

we see stars orbiting the center of the Milky Way Galaxy with extreme speeds

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

Once a black hole forms, the size of the event horizon is determined only by

the mass of the black hole

The region around a black hole within which everything is trapped is called

the event horizon

According to Einstein's general theory of relativity, the stronger a star's gravity,

the slower time runs near it

What scientific data from 1919 supported Einstein's theory of gravity over Newton's theory?

observing starlight passing close to the Sun during an eclipse

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

the Earth would keep orbiting as it currently does

According to the general theory of relativity, the presence of mass

causes a curvature (or warping) of spacetime

When astronauts aboard the International Space Station (ISS) in space let go of an orange, it just floats there. Why is that?

the ISS is falling around the Earth, and in free fall, things feel no weight

What ghostly particles did we detect from Supernova 1987A, helping to confirm our core-collapse supernova model?

neutrinos

Which of the following is smallest in size (radius)?

neutron star

The maximum possible mass for a white dwarf is about 1.4 solar masses. This is known as

the Chandrasekhar limit

A white dwarf, compared to a main sequence star with the same mass, would always be

smaller in radius

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

a white dwarf

How do massive stars enrich the interstellar medium for subsequent generations of stars and planets?

massive stars evolve quickly compared to low-mass stars, releasing a lot of material containing helium and heavier elements

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

iron

The rapid onset of helium fusion in the core of a low-mass star is called

the helium flash

What will happen to the Sun when it is in its planetary nebula phase?

it will decrease in mass by expelling its outer layers

When the core of a star reaches a temperature of about 100 million degrees (K), what new event happens?

three helium nuclei fuse to form carbon (element number 6)

On an H-R diagram of a cluster of stars, what is used as a good indicator of the cluster's age?

the point on the main sequence where stars begin to 'turn off' to move toward the red giant region

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

all of the above stars have fusion in their cores

Why is it so difficult for astronomers to see new stars in the process of birth?

most stars are born inside dusty clouds, which block any light that may be coming from the stars

A star whose temperature is increasing but whose luminosity is roughly constant moves in what direction on the H-R diagram?

to the left on the H-R diagram

If you want to find stars that are just being born, where are the best places to search?

in giant molecular clouds

A star has a parallax angle of 0.2 arcseconds. How far away is the star from us?

5 parsecs

What property of a star is most important in determining its main-sequence lifetime?

its mass

Stars are on the main sequence when

they are fusing hydrogen to helium in their cores

Most of the stars (nearly 90 percent) on a Hertzsprung-Russell diagram are found in a region called

the main sequence

In which part of the Hertzsprung-Russell diagram do the stars have the largest radius?

upper right (low temperature, high luminosity)

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

surface temperature and luminosity

Which of the following stars appears the reddest and has the lowest surface temperature?

Betelgeuse, a supergiant star (spectral type: M)

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

its apparent brightness and distance

Two stars have the same luminosity, but star B is three times farther away from Earth than star A. Compared to star A, star B will look

nine times fainter than star A

The luminosity of a star is

how much energy the star gives off every second

Which of the following is NOT true about the Sun's core?

photons emanate from the core and mostly travel freely out of the Sun

When two light elements collide to undergo nuclear fusion,

some of the mass is converted to energy

In the formula E = mc2, the symbol c stands for

the speed of light

Why do sunspots appear darker than their surroundings?

they are cooler than their surroundings

The part of the Sun that you can see directly on a blue sky sunny day is called its

photosphere

Which of the following kinds of telescopes can be used only above the Earth's atmosphere?

X-ray telescope

A red photon has a higher _________ than a blue photon.

wavelength

What property primarily determines the amount and types of electromagnetic radiation emitted by objects in the Universe?

their temperature

Which of the following statements about the nucleus of a typical atom is FALSE?

the nucleus repels the electrons that move around it

Which of the following puts the electromagnetic spectrum in order of increasing wavelength?

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

To leave the Earth's gravitational pull and explore the Solar System, you must have

escape velocity

When a comet like Hale-Bopp is at the point in its orbit that is closest to the Sun

it is at perihelion and traveling its fastest

Newton's version of Kepler's 3rd law allows us to determine the masses of objects orbiting each other if we measure:

their period of revolution and the distance between them

Newton showed that to change the direction in which an object is moving, one needs to

apply a force

If the Moon were twice as far from the Earth as it is, the force of gravity attracting the Moon to the Earth would be

25% (one-quarter) as strong

Which of Galileo's observations was most decisive in favor of the Copernican model?

seeing the phases of Venus

When a planet in its orbit is closer to the Sun, it

moves faster than when it is farther away from the Sun

Kepler's major breakthrough in understanding planetary motion came when he

explored elliptical orbits rather than just circular orbits

When it comes to our place in the solar system today, which model do we accept?

heliocentric

When a planet temporarily moves westward in the sky over the course of several weeks or months, we call it:

retrograde motion

What would you have to change about the Earth to stop our planet from having significantly different seasons?

the tilt of its axis

Approximately what time does the full moon rise?

sunset

How long is it from first quarter moon to full moon?

about one week

The south celestial pole and the north celestial pole lie in the sky directly above

the Earth's rotation axis

The Sun's apparent path around the celestial sphere is called

the ecliptic

In summer, the Earth's axis points toward the star Polaris. In winter,

the axis still points towards the star Polaris

In Australia (in the Southern Hemisphere), when are the days the shortest and the nights the longest?

in late June

In locating points on the Earth, we call the number of degrees east or west of Greenwich, England its:

longitude

The latitude of the Earth's equator is

0 degrees

A light year is

the distance that light travels in one year

All the stars you see with your unaided eye on a dark night sky are

in the Milky Way Galaxy

The Earth is located within

all of the above

The Astronomical Unit (AU) as defined by astronomers is

the average distance between the Earth and the Sun

The star that provides energy for life on Earth is

the Sun