ASTR 264 Exam 2

Of stars with these masses, which star spends the longest time as a main-sequence star?

.5 solar masses

if the earth were to shrink in size until it became a black hole, its schwarzschild radius would be

1 cm

You measure that an object has a mass of exactly 1 kg by weighing it in the Earth's gravitational field. The equivalence principle says that the mass you would measure by trying to accelerate it would be:

1 kg

The Ring Nebula is a planetary nebula that currently has a radius of 1.2 x 10^13 km and an expansion velocity of 250 km/s. Approximately how long ago did its parent star die and eject its outer layers?

1,500 years ago

A Type I supernova occurs when a white dwarf exceeds a mass of:

1.4 solar masses

A Type I supernova has a luminosity of approximately:

10 billion times the sun's luminosity

Let's take the Hubble parameter (the Hubble constant) to be 70 km/s/Mpc. If a galaxy has an apparent velocity of 700 km/s, what is its distance?

10 mpc

If the Milky Way formed stars at approximately a constant rate over the last 14 billion years, what fraction of the M-type stars that ever formed in it can still be found as main-sequence stars today? Note that M-type stars have a mass of approximately 0.5 solar masses.

100 percent

Approximately how long does it take the photons released in nuclear reactions in the core of the Sun to exit the photosphere?

100,000 years

If you observe a maximum number of sunspots these days, how long would you have to wait to see a lot of sunspots during the next solar maximum?

11 years

The Sun's magnetic field reverses direction every:

11 years

The Schwarzschild radius of a 10 solar mass black hole is __________ the size of the Schwarzschild radius of a 5 solar mass black hole.

2 times

Sun's mass

2x1030 kg

The cosmic microwave background radiation was emitted when the universe had a size about 1/1000 of today's value. What was the temperature of the microwave background radiation when it was emitted?

3000 K

The Sun's corona has a temperature of approximately 1 million degrees. At what wavelength and in what part of the electromagnetic spectrum does its radiation peak?

3x10^9 m, X-rays

The strength of gravity on the surface of the Earth is expressed as the gravitational acceleration, g = 9.8 m/s2. Now, let us denote the mass of a neutron star as MNS and its radius as RNS. The strength of gravity on its surface is given by the formula g = GMNS/R2NS. Calculate the acceleration of gravity on a neutron star of 3 solar masses and a radius of 10 km. Then express this in terms of the gravitational acceleration on Earth, g. Thus, calculate how much stronger gravity on a neutron star feels compared to gravity on Earth. You can find the various needed constants e.g. on Wikipedia.

4 x 10^11

Take the mass of a hydrogen nucleus as 2x10-27 kg and that of a helium nucleus as 7x10-27 kg. The mass difference between 4 hydrogen nuclei and 1 helium nucleus is 5x10-29 kg. Further, assume that the Sun fuses 7x1011 kg of helium each second. Note that 1 Watt = 1 m2 kg/s3 and the speed of light is 3x108 m/s. What is the luminosity of this star, i.e. how much power does it churn out?

4.5x1026 Watt

When will the sun most likely stop being a main sequence star?

5 billion years

Suppose 100 new stars are created in the Milky Way every year. Suppose further that only 1 out of 5,000 stars will be massive enough to explode as a supernova. What would be the average time between supernova explosions in the Milky Way?

50 years

The Type II supernova that created the Crab Nebula was seen by Chinese and Arab astronomers in the year 1054 CE. Because the star is 6,500 light-years away from us, we know the star exploded in the year:

5447 BC

If the distance of a galaxy at a redshift z = 0.5 is 1,800 Mpc, how many years back into the past are we looking when we observe this galaxy?

6 billion years

If an 0.8 solar mass white dwarf could accrete matter from a binary companion at a rate of 10-9 solar masses per year. How long would it take before it exploded as a Type I supernova?

600 million years

If the distance of a galaxy is 10 Mpc, what is its recessional velocity if the Hubble constant is 70 km/s/Mpc?

700 km/s

Astronomers have known that galaxies are separate entities outside of our own for roughly the last:

90 years

Sitting in a 100°F hot tub feels much hotter than standing outside on a 100°F day. This analogy illustrates why...?

An astronaut would feel cold standing in a 106 K intercloud gas. You can easily touch a burning fluorescent light bulb, but not a burning incandescent bulb.

Why is 21-cm radiation a good tracer of spiral arm structure?

Emitted by neutral hydrogen, it traces the location of high concentrations of gas.

Why is it not possible to look all the way back to the Big Bang itself?

For redshifts of z > 1,000, photons are heavily altered because they easily react with individual protons and electrons in the universe.

What do astronomers mean when they say that the universe is homogeneous?

Galaxies are generally distributed similarly throughout the universe.

Two elliptical galaxies have the same apparent size and brightness. Galaxy A appears lumpy, and it is possible to observe individual stars and star clusters. The other one, galaxy B, appears very smooth, with no fine detail. Which one is likely to be more luminous?

Galaxy B. This galaxy appears smooth because it is farther away and the light from its stars all blends together. Because it is farther away, it has to be more luminous

If you wanted to study regions where star formation is currently happening you could use:

H-alpha emission to look for O and B stars 21 cm radiation to find neutral hydrogen clouds radio emission from carbon monoxide (CO) to find molecular cloud cores infrared emission to identify T Tauri stars

Why is hydrogen burning the main energy source for main-sequence stars?

Hydrogen is the most common element in stars. Hydrogen nuclei have the smallest positive charge. Hydrogen burning is the most efficient of all fusion or fission reactions. Hydrogen can fuse at temperatures lower than other elements.

Where have astronomers observed the existence of planets?

In our solar system orbiting stars other than the sun orbiting stars in binary systems traveling on their own through the milky way, not orbiting a star

The claim-to-fame of Supernova Refsdal is that:

It has been observed at different times, through various gravitational lenses.

What is the meaning of the Schwarzschild radius around a black hole?

It is the radius at which the escape velocity equals the speed of light.

Name one verified prediction of general relativity.

Mercury's orbital precession is a little bigger than predicted by Newtonian physics.

How does relativity compare to Newtonian physics?

Relativity gives the same result as Newtonian physics when objects are moving slowly.

(t/f)

Star formation in a molecular cloud can be slowed by the strength of its magnetic field and turbulence caused by supernovae and stellar winds from massive stars.

The temperature of the CMB is hotter on one side of the sky than on the other by approximately 3 mK. What does this tell us?

The Earth has a peculiar velocity of about 400 km/s with respect to the CMB.

What do astronomers mean when they say that the Sun makes energy by hydrogen burning?

The Sun is fusing hydrogen into helium and releasing energy.

Which of the following can be a result of an increase in solar activity?

The altitudes of orbiting satellites decrease. Airplanes have trouble navigating. Stronger auroras are seen. Power grids can be damaged.

If a collapsing interstellar cloud formed only a protostar without an accretion disk around it, what would happen?

The forming protostar would be rotating too fast to hold itself together.

In the lecture we have seen a demonstration using a spandex sheet. In this model, a black hole would correspond to...

The spandex being pulled down to form a very thin well with very steep slopes.

What do astronomers mean when they say that the universe is isotropic?

The universe looks the same no matter what direction you look.

In the rubber-sheet analogy for spacetime, what would you expect for objects (such as golf balls) rolling around in the presence of a massive object that is stretching the rubber sheet?

Their paths would curve more the closer they come to the massive object.

What are observational evidences for the existence of galaxy clusters?

Very bright X-ray sources, which indicate the presence of the hot gas found in galaxy clusters. Small deviations of the Cosmic Microwave Background (CMB) from its blackbody temperature of 2.7 K caused by CMB photons interacting with the hot gas in galaxy clusters. Over-densities of galaxies on the sky, corresponding to their being bound gravitationally. Gravitational lensing of background sources by galaxy clusters.

The gravitational redshift of light should be smallest for light emitted from the surface of:

a planet like the earth

inertial frame of reference

a reference frame that is not accelerating

Hawking radiation is emitted by a black hole when:

a virtual pair of particles is created from the vacuum of space

The Maunder Minimum was a 60-year period when:

almost no sunspots occurred on the Sun

An accretion disk forms around a collapsing protostar because infalling material must conserve:

angular momentum

Spiral structure can be triggered in a disk galaxy by:

any disturbance to the disk

Gravitational lensing occurs when __________ distorts the fabric of spacetime.

any massive object

Stars in elliptical galaxies have velocities that:

are oriented in random directions

compared to a clock on the surface of the earth, a clock on the international space stations runs...

at approximately the same rate, only a tiny bit slower

equivalence principle

being stationary in a gravitational field is the same as being in an accelerated reference frame

A red giant star is found to be orbiting an unseen object with a short orbital period. By measuring the speed at which it orbits, astronomers deduce that the object has a mass of 10 solar masses. This object is probably a __________ because __________.

black hole; its mass is too large to be a neutron star or a white dwarf

A _________ is a failed star that shines primarily because of energy derived from its gravitational collapse rather than nuclear burning.

brown dwarf

Most black holes are found:

by the X-rays produced by a surrounding accretion disk

Which of the following was NOT created as a result of Big Bang nucleosynthesis?

carbon

A 1 solar-mass star in a binary system could create the following chemical element and eject it into the interstellar medium:

carbon helium iron gold

What did Edwin Hubble study in the Andromeda Galaxy that proved it was an individual galaxy and not part of our own Milky Way?

cepheid stars

f you hold on to one end of a metal spoon while placing the other end in a pot of boiling water, you will burn your hand. This is an example of energy being transported by:

conduction

If you observed that at the centers of some galaxies there were objects emitting lots of X-rays or there was gas in rapid motion, you might conclude that these galaxies:

contain black holes

Active star formation does not occur in elliptical galaxies because they:

contain little molecular hydrogen

When you turn on the heater in a car, the passengers in the front seat warm up first, then eventually the warm air gets to the passengers in the back seat. This is an example of energy being transported by...

convection

Which of the layers of the Sun is located the furthest from the center of the Sun?

corona

spiral galaxies have _____ halos

dark matter

The Sun's internal magnetic field becomes tangled up over time because of:

differential rotation

astronomers use galactic redshift as a measure of...

distance

Which of the following is a consequence of Einstein's special theory of relativity?

distances are shorter for objects traveling close to the speed of light

In a white dwarf, what is the source of pressure that halts its contraction as it cools?

electrons packed so closely that they become incompressible

according to Einstein's relativity, which two quantities are different manifestations of the same thing?

energy and mass

Where in the universe did the Big Bang take place?

everywhere in the universe

A person would feel __________ as she approached the event horizon of a black hole.

extremely strong tidal forces

(t/f) Charles Messier published the first galaxy catalog containing over 2,000 nearby galaxies.

false

(t/f) Einstein's special theory of relativity implies that if a person standing at the front of a train traveling at 0.1 km/s shines a flashlight out in front of the train, the emitted photons will travel at a speed of 300,000.1 km/s.

false

(t/f) Elliptical galaxies have the shapes they do because all the stars are orbiting in the same direction in the galaxy

false

(t/f) Fusion reactions that create chemical elements heavier than oxygen require energy input; thus, these reactions cannot provide a star with power.

false

(t/f) In the radiative zone inside the Sun, photons are transported from the core to the convective zone in a matter of seconds.

false

(t/f) Neutrinos are particles with small masses that interact easily with normal matter.

false

(t/f) Nuclei of atoms are held together by gravity.

false

(t/f) Once the core of a low-mass main-sequence star runs out of hydrogen, fusion in the star stops until the core temperature is high enough for helium fusion to begin.

false

(t/f) One result of relativity is that an astronaut in a windowless spacecraft could tell the difference between falling freely and the presence of a nearby gravitational source.

false

(t/f) The Sun could turn into a black hole at the end of its life.

false

(t/f) The apparent recessional velocities of galaxies at large distances are due mainly to the actual motions of the galaxies through space.

false

(t/f) The current temperature of the cosmic microwave background radiation is 17 K.

false

(t/f) The densest state of matter found in nature occurs inside a white dwarf star.

false

(t/f) The more massive a star is, the more hydrogen it has to burn, and the longer its main-sequence lifetime lasts.

false

(t/f) We can measure the value of the Hubble Parameter H0 (the "Hubble Constant") directly, without any intermediate steps.

false

(t/f) We know from our best physics theories that the center of a Black Hole is a point of infinite density.

false

(t/f) stars forming in the molecular clouds tend to form first in the low-density periphery

false

(t/f) the sun eventually could become a nova

false

We can identify only a fraction of all the radio pulsars that exist in our galaxy because:

few swing their beam of synchrotron emission in our direction

The net effect of the proton-proton chain is that four hydrogen nuclei are converted to one helium nucleus and _________ are released.

gamma ray photons, positrons, and neutrinos

The bending of light passing near a massive object is called:

gravitational lensing

the source of energy for a contracting protostar comes from what?

gravitational potential energy

General relativity predicts that pairs of objects with nonzero masses undergoing accelerations can produce:

gravitational waves

the result of mass distorting the fabric of spacetime

gravity

When a star depletes its core supply of hydrogen, _________ causes the core to collapse while increased gas _________ is exerted on the atmosphere.

gravity; pressure

Approximately __________ of the observed spiral galaxies are barred.

half

As a main-sequence star burns its core supply of hydrogen, what happens?

helium builds up as ash in the core

If you could watch stars forming out of a gas cloud, which stars would form first?

high mass stars

During which phase of the evolution of a low-mass star does it have two separate regions of nuclear burning occurring in its interior?

horizontal branch

a protostar's evolutionary "track" in the HR diagram traces out ...

how the protostar's luminosity, temperature, and radius change with time

We classify galaxies by:

how they appear on the sky

the gas in a planetary nebula is composed of:

hydrogen and heavier elements like helium and carbon processed in the core of the post-asymptotic giant branch star

a main sequence star is unique why?

hydrogen burning occurs in its core

why are brown dwarfs considered failed stars?

hydrogen fusion never begins in their cores

According to relativity, spacecraft that can travel faster than the speed of light are:

impossible, because nothing can travel that fast

The energy that fuels the Sun is generated where?

in its core

The Sun is 27 percent helium by mass. Where was the majority of this helium manufactured?

in the big bang

a gravitational lens can...

increase the brightness of an object that is located behind the lens can magnify or change the apparent shape of an object that is located behind the lens

as a protostar evolves, it's temperature does what?

increases due to the kinetic energy of infalling material

According to Hubble's law, as the distance of a galaxy __________ its __________ increases.

increases; recessional velocity

By studying how the surface of the Sun vibrates like a struck bell we can determine its:

interior density

an iron core cannot support a massive main-sequence star because:

iron cannot fuse to make heavier nuclei and produce energy

21-cm radiation is important because:

it allows us to study neutral hydrogen in the interstellar medium

As a white dwarf star gradually cools, its radius stays approximately constant. What is happening to the white dwarf's luminosity?

it decreases

spacetime

it is the combined treatment of space and time in the theory of relativity

why can an object with a nonzero mass never travel as fast as the speed of light?

it would take an infinite amount of energy to accelerate it to a speed of c

what does gravity mean in relativity?

it's the result of the distortion in spacetime around an object with any energy density

what happens as a protostar contracts?

its density rises its temperature rises its radius decreases its pressure rises

Which of the following is NOT a common characteristic of a neutron star? large radius enormous magnetic field source of pulsars very short rotation period extremely high density

large radius

Asymptotic giant-branch stars have _________ luminosities, _________ radii, and _________ escape velocities.

large; large; small

the most common types of stars in our galaxy

low mass stars

To be a standard candle, an object must have a constant:

luminosity

What are two ways that Type I supernovae can be produced?

mass transfer and stellar mergers

A surprising fact about a one-solar-mass protostar is that, even though nuclear reactions have not yet started in their cores, they are _________ than the Sun.

more luminous

The spectra of most galaxies tell us that:

most galaxies appear to be moving away from us

Stars in the disks of spiral galaxies have orbits that:

mostly aligned in the same plane

The existence of the cosmic microwave background radiation tells us that the early universe was:

much hotter than it is today

Which of these can travel directly from the center of the Sun to Earth in about 8 minutes?

neutrinos

Is dark energy responsible for the expansion of the universe?

no the expansion would happen without dark energy, but dark energy is causing the expansion rate to increase

When two atomic nuclei come together to form a new species of atom, this is called:

nuclear fusion

What critical event transforms a protostar into a normal main-sequence star?

nuclear fusion begins in the core

Where did the iron in your blood come from?

nucleosynthesis in the cores of massive stars

Iron has 26 protons in its nucleus, and gold has 79 protons. Where did all the gold on the Earth come from?

nucleosynthesis that took place in supernova explosions

Sort distance indicators that are used to measure distances, ranging from the very nearest to the very farthest.

parallax main sequence fitting cepheids type I supernova

The Crab Nebula is an important test of our ideas about supernova explosions because:

people saw the supernova and later astronomers found a pulsar inside the nebula

After the Big Bang, when the universe cooled and protons and electrons combined so that the universe became neutral, what important consequence happened?

photons began to travel freely through the universe

In the early 1960s, physicists named Penzias and Wilson detected a persistent noise at a wavelength of 1 mm in their radio telescope that came from all directions in the sky due to:

photons left over from the big bang

Hydrostatic equilibrium is a balance between what?

pressure and gravity

The entire process of star formation is really just an evolving balance between:

pressure and gravity

Gamma-ray bursts are likely to be:

produced by the most energetic supernova explosions

When the core of a massive star collapses, a neutron star forms because:

protons and electrons combine to make neutrons

Molecular cloud cores are places where you might find:

protostars Herbig-Haro objects molecular hydrogen (H2) carbon monoxide (CO)

Our Sun is unique compared to the other stars in our galaxy because of its...

proximity

Some restaurants place food under infrared heat lamps so that it stays warm after it has been cooked. This is an example of energy being transported by...

radiation

interstellar stars

regions where hydrogen tends to be denser than the surrounding gas

The spiral structure seen in many galaxies:

rotates at a speed that is different than the gas in the disk

massive stars explode when they ...

run out of nuclear fuel in their core, and the cores collapse

One star in a binary will almost always become a red giant before the other because:

small differences in main-sequence masses yield large differences in main-sequence ages

Why are some galaxies' spectra blueshifted rather than redshifted?

some nearby galaxies have small peculiar velocities in our direction

Galaxies move away from us in all directions because:

space is expanding

Type I and Type II supernovae can be distinguished by what combination of observations?

spectra and light curves

According to the conservation of angular momentum, if an ice skater starts spinning with her arms out wide, then slowly pulls them close to her body, this will cause her to:

spin faster

Because angular momentum must be conserved, as a gas cloud contracts due to gravity it will also:

spin faster

An Einstein Cross is a particular example of what?

strong gravitational lensing

Which force is responsible for holding the protons and neutrons in the nucleus of an atom together?

strong nuclear force

Which of the following is responsible for heating the bulk of the very hot intercloud gas?

supernovae

The principal means by which high-mass stars generate energy on the main sequence is called:

the CNO cycle

The detection of solar neutrinos confirms what?

the Sun's core is powered by proton-proton fusion

Planetary nebula

the ejected envelope of a giant star surrounding the remnant of a stsar

Which of the following is NOT a prediction of the standard Big Bang theory that has been successfully verified by observations?

the most distant galaxies are redder because they are older

For low-mass main-sequence stars in hydrostatic equilibrium, at any interior radius there exists a balance between the downward gravitational force at that radius and:

the outward gas pressure from the material inside that radius

geodesic

the path followed by a freely falling object in spacetime

hawking radiation from black holes

the radiation of particles created near the event horizon

Which of the following layers of the Sun makes up the majority of its interior?

the radiative zone

event horizon of a black hole

the radius at which the escape speed from the black hole equals the speed of light

As a subgiant star becomes a red giant, its luminosity increases while its temperature remains approximately constant. What does this mean?

the radius is increasing

Hubble's constant, H0, represents:

the rate of expansion of the universe (at current times)

What will observers in different inertial frames of reference always agree on?

the results of physics experiments performed in each frame

If the Sun were to be instantly replaced by a 1 solar-mass black hole, the gravitational pull of the black hole on Earth would be:

the same as it is now

If we lived in a galaxy one billion light-years from our own, what would we see?

the same universe we see here

How does one know that multiple images in strong gravitational lensing really show one and the same distant galaxy?

the spectra of the lensed galaxies are all the same

In the Great Debate of 1920, Curtis and Shapley argued over whether or not:

the spiral nevulae were located outside the milky way

What would happen if mass were continually added to a 2 solar-mass neutron star?

the star could eventually become a black hole

What keeps the gas in the Sun's corona from flying away from the Sun?

the sun's magnetic field

Helium burns in the core of a horizontal branch star via _________ and produces _________.

the triple alpha reaction ; carbon

the hubble classification scheme for galaxies sorts them how?

their visual appearance

why do astronauts in space feel no gravity?

they and their spaceship are both freely falling at the same rate in the gravitational field

What is more massive, a kg of lead or a kg of neutron star material?

they are both the same

Elliptical galaxies appear red because:

they contain mostly old stars

Asymptotic giant branch stars have high-mass loss rates because:

they have low surface gravity

What primarily makes it difficult to observe protostars?

they occur in dusty regions

Even if a black hole emitted no light, we can still detect it:

through its gravitational effect on surrounding gas or stars

In spiral galaxies, the size of the central bulge is correlated with the:

tightness of the spiral arms

The inverse of the value of the Hubble parameter H0 is a:

time

(t/f) A black hole can be produced if the stellar core left over after a supernova is larger than 3 solar masses.

true

(t/f) A star like the Sun will eventually become an electron degenerate white dwarf star.

true

(t/f) Although elliptical and irregular galaxies have been observed in both dwarf and giant varieties, we find only giant spiral galaxies.

true

(t/f) At the center of the Sun, the temperature is roughly 15 million K.

true

(t/f) Elliptical galaxies contain hot gas that is heated by supernova explosions.

true

(t/f) Gravitational lensing allows us to see distant objects brightened and distorted because of massive objects in the path that the light from the object travels.

true

(t/f) Gravity is nothing more than a curvature in the fabric of spacetime.

true

(t/f) If coronal holes covered a larger fraction of the Sun's surface, the solar wind would contain a higher density of particles.

true

(t/f) In protoplanetary environments, the plane of an accretion disk is perpendicular to the axis of rotation of the interstellar cloud out of which it forms.

true

(t/f) Molecular hydrogen atoms are found only inside dense clouds where they are shielded from stellar radiation.

true

(t/f) Special relativity says that all observers moving at constant speed will measure the same value of the speed of light.

true

(t/f) Stars with masses similar to the Sun will lose approximately 30 percent of their mass before they become white dwarfs.

true

(t/f) The 3-D shape of an elliptical galaxy depends on the average velocity of its stars along each of the three axes.

true

(t/f) The CMB contains photons left over from the epoch in the universe's history when electrons recombined with nuclei.

true

(t/f) The average density of the interstellar medium is many times less dense than the best vacuum on Earth.

true

(t/f) The cosmological principle says physical laws that the universe is homogeneous and isotropic.

true

(t/f) The fact that the surface of the Sun rings like a bell lets us understand its interior better.

true

(t/f) The singularity of a black hole has a tiny radius, but its event horizon is finite.

true

(t/f) The temperature of the corona is much hotter than any other layer in the solar atmosphere.

true

(t/f) There is no special center to the expansion of the universe.

true

(t/f) We observe neutral hydrogen gas using 21-cm emission.

true

(t/f) When we measure distances to very faint galaxies with Type I supernovae, the accuracy of the measurement is only as good as that of the calibration of Cepheid stars.

true

(t/f) You have a 1 kg mass at rest sitting on a lab bench in front of you. You see somebody fly by in a spaceship traveling at 0.2c. That astronaut flying by also has a 1 kg mass sitting on a bench in front of her. She would measure that mass to be 1kg.

true

(t/f) every pulsar is a neutron star, but not every neutron star is a pulsar

true

(t/f) special relativity says that moving clocks run slower

true

(t/f) the sun will become a red giant star in about 5 billion years

true

(t/f) type I and type II supernovae are approximately equal im luminosity

true

(t/f) when winds blow the gas away from a forming protostar it becomes visible as a T tauri star

true

In a sunspot, the umbra is cooler than the penumbra. (t/f)

true

The mass of an atomic nucleus is a measure of how much energy is contained therein. (t/f)

true

The percentage of hydrogen in the Sun's core today is roughly half of what it was originally.

true

stars evolve primarily because they use up the fuel in their cores (t/f)

true

Which distance indicator can be used to measure the most distant objects?

type I supernovae

Why can Type I supernovae be used to determine a galaxy's distance?

type I supernovae have approximately the same luminosity

What ionizes the gas in a planetary nebula and makes it visible?

ultraviolet photons emitted by a white dwarf

The darkest part of a sunspot is called the:

umbra

Black holes that are stellar remnants can be found by searching for:

variable x-ray sources

Dust in the ISM appears dark in _________ wavelengths and bright in _________ wavelengths.

visible; infrared

We know the Sun's corona is very hot because:

we observe absorption from highly ionized atoms of iron and calcium in its spectrum

When do the predictions of special relativity match those of Newtonian physics?

when objects are moving too slowly

When is the Sun most luminous?

when there are a maximum number of sunspots

One consequence of Einstein's ideas about the speed of light is that:

whether events are seen as simultaneous or not depends on the motion of an observer

Type I and Type II supernovae are respectively caused by what types of stars?

white dwarfs, massive stars

You observe a distant galaxy, and see that most of the blue light is coming from regions along spiral arms and in the outer regions of the galaxy. This blue light indicates that these regions contain:

young, massive stars