Stars and Galaxies Midterm

The ________ is the thin shell of the Sun's gases that we normally see, forming the lowest level of its atmosphere.

photosphere

________ are features produced by the convection of gas from below the photosphere.

granules

The ________ is a layer of hotter, but less dense, gas above the photosphere.

chromosphere

________ are jets of gas that rise up into the chromosphere along the boundaries of supergranules.

spicules

The ________ is the outermost layer of gases in the solar atmosphere, extending outward to become the solar wind at great distances from the Sun.

corona

The ________ refers to how some surface features on the Sun vary periodically in an 11-year cycle.

solar cycle

________ are relatively cool regions produced by local concentrations of the Sun's magnetic field protruding through the photosphere.

sunspots

A ________ is gas lifted into the Sun's corona by magnetic fields.

prominence

A ________ is a brief, but violent, eruption of hot, ionized gases from a sunspot group

solar flare

________ send out large quantities of gas from the Sun and can affect satellites, communication, and electric power when directed toward Earth.

Coronal mass ejections

The ________ suggests that many transient features of the solar cycle are caused by the effects of differential rotation and convection on the Sun's magnetic field.

magnetic dynamo model

________ is the thermonuclear process that produces the Sun's energy, in which four hydrogen nuclei release energy when they fuse together to produce a single helium nucleus.

Hydrogen fusion

The energy released in a thermonuclear reaction comes from the conversion of matter into energy, according to Einstein's equation ________.

E = mc²

The ________ is a theoretical description of the Sun's interior derived from calculations based on the laws of physics.

solar model

Throughout most of the Sun's interior, energy moves outward from the core by ________. In the Sun's outer layers, energy is transported to the Sun's surface by convection.

radiative diffusion

The amount of energy the Sun emits has ________ by about 30% since it first formed.

increased

A ________ is a hypothetical object that completely absorbs all the electromagnetic radiation that strikes it.

blackbody

________ states that the peak wavelength of radiation emitted by a blackbody is inversely proportional to its temperature.

Wien's law

A ________ shows the intensities of radiation emitted at various wavelengths by a blackbody at a given temperature.

blackbody curve

The ________ shows that a hotter blackbody emits more radiation at every wavelength than does a cooler blackbody.

Stefan–Boltzmann law

________ is the study of electromagnetic spectra and provides important information about the chemical composition of remote astronomical objects.

Spectroscopy

Kirchhoff's three laws describe the conditions under which ________, ________, and a continuous spectrum can be observed.

absorption lines, emission lines

Spectral lines serve as distinctive "________" that identify the chemical elements and molecules comprising a light source.

fingerprints

An atom consists of a small, dense nucleus surrounded by ________

electrons

________ describes the behavior of particles and shows that electrons can only be in certain allowed orbits around the nucleus.

Quantum mechanics

The spectral lines of atoms correspond to the various ________ between allowed orbits of that element.

electron transitions

The ________ in hydrogen's spectrum at visible wavelengths arises from electron transitions between the second energy level of the hydrogen atom and higher levels.

Balmer series

The ________ occurs when the motion of an object toward or away from an observer causes the observer to see all of the colors from the object blueshifted or redshifted, respectively.

Doppler shift

________ is motion across the sky, which yields no Doppler shift.

Proper motion

________ is the apparent shift of a star's location against the background stars while Earth moves along its orbit around the Sun.

Stellar parallax

The ________ of a star, denoted m, is a measure of how bright the star appears to Earth-based observers.

apparent magnitude

The ________ of a star, denoted M, is a measure of the star's true brightness and is directly related to the star's energy output, or luminosity.

absolute magnitude

The ________ of a star is the amount of energy it emits each second

luminosity

Stellar temperatures can be determined from stars' ________ or stellar spectra

colors

Stars are classified into ________ (O, B, A, F, G, K, and M) based on their spectra or, equivalently, their surface temperatures.

spectral types

The ________ diagram is a graph on which luminosities of stars are plotted against their spectral types (or, equivalently, their absolute magnitudes are plotted against surface temperatures).

Hertzsprung–Russell (H-R)

The four major groupings of stars shown in the H-R diagram are ________, ________, ________, and ________.

main-sequence stars, giants, supergiants, white dwarfs

The ________ expresses a direct correlation between a main-sequence star's mass and the total energy it emits.

mass-luminosity relation

In the H-R diagram, stars are classified in order of decreasing temperature as types ________, ________, ________, ________, ________, ________, and ________.

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

On the H-R diagram, main-sequence stars form a diagonal band from the ________ (hot, luminous stars) to the ________ (cool, dim stars).

upper left, lower right

The majority of stars in the H-R diagram are found in the ________ group.

main-sequence

When plotted on the H-R diagram, ________ stars appear above the main sequence because they have larger radii and thus greater luminosity than main-sequence stars of the same temperature.

giant

________ is a method of determining distances to stars using their spectral types and luminosity classes on the H-R diagram.

Spectroscopic parallax

________ are pairs of stars that orbit each other.

Binary stars

The masses of the two stars in a binary system can be computed from measurements of the ________ and ________ of the system.

orbital period, orbital dimensions

A ________ is a binary system detected from the periodic shift of its spectral lines.

spectroscopic binary

An ________ is a binary system whose orbits are viewed nearly edge-on from Earth, so that one star periodically eclipses the other.

eclipsing binary

________ are enormous, cold clouds of gas and dust scattered about the disk of the Galaxy.

Giant molecular clouds

________ are clumps of gas and dust that coalesce in Bok globules within a giant molecular cloud, beginning the process of star formation.

Protostars

When a protostar's contraction slows down, it becomes a ________. When its core temperature reaches 10 million K, hydrogen fusion begins and it becomes a main-sequence star.

pre-main-sequence star

The most massive pre-main-sequence stars take the ________ time to become main-sequence stars, while the least massive pre-main-sequence stars take the ________ time.

shortest, longest

In the final stages of pre-main-sequence contraction, G, K, and M stars that undergo vigorous chromospheric activity are called ________.

T Tauri stars

A(n) ________ is a collection of a few hundred or a few thousand newborn stars formed in the plane of the Galaxy.

open cluster

The Sun has been a main-sequence star for 4.6 billion years and will remain so for about another ________ years.

5 billion

Less massive stars than the Sun evolve ________ and have ________ main-sequence lifetimes. More massive stars than the Sun evolve ________ and have ________ main-sequence lifetimes.

more slowly, longer, more rapidly, shorter

When hydrogen in the core of a main-sequence star is gone, it leaves a core of nearly pure ________ surrounded by a shell where hydrogen fusion continues.

helium

When the central temperature of a giant reaches about 100 million K, the thermonuclear process of ________ begins, converting helium to carbon, then to oxygen.

helium fusion

In a massive giant, helium fusion begins gradually. In a less massive giant, it begins suddenly in a process called the ________.

helium flash

Relatively young stars are metal-rich (); ancient stars are metal-poor ()

Population I, Population II

Groups of hundreds of thousands to millions of stars formed together from a common interstellar cloud are called ________.

globular clusters

The age of an open or globular star cluster can be estimated by plotting its stars on a(n) ________ diagram.

H-R

When a star's evolutionary track carries it through a region called the ________ in the H-R diagram, the star becomes unstable and begins to pulsate.

instability strip

________ are low-mass, pulsating variables with short periods.

RR Lyrae variables

________ are higher-mass, pulsating variables exhibiting a regular relationship between the period of pulsation and luminosity.

Cepheid variables

Stars with higher masses fuse more ________ into existence than do stars with lower masses

elements

Stars lose mass via ________ throughout their lives.

stellar winds

A low-mass main-sequence star becomes a ________ when hydrogen shell fusion begins

giant

The burned-out core of a low-mass star becomes a dense carbon-oxygen body, called a ________, with about the same diameter as that of Earth.

white dwarf

The maximum mass of a white dwarf (the Chandrasekhar limit) is ________ M☉

1.4

Explosive hydrogen fusion occurs on the surface layers of white dwarfs in some close binary systems, producing sudden increases in luminosity that we call ________.

novae

An accreting white dwarf in a close binary system can become a ________ when carbon fusion ignites explosively throughout such a degenerate star.

Type Ia supernova

After exhausting its central supply of hydrogen and helium, the core of a high-mass star undergoes a sequence of other thermonuclear reactions, eventually producing an ________ core.

iron

A high-mass star dies in a(n) ________ explosion that ejects most of the star's matter into space at very high speeds.

supernova

Neutrinos were detected from ________, which was visible to the naked eye. Its development supported theories of Type II supernovae.

Supernova 1987A

The core of a high-mass main-sequence star containing between 8 M☉ and 25 M☉ becomes a ________.

neutron star

A ________ is a rapidly rotating neutron star with a powerful magnetic field tilted relative to the star's rotation axis.

pulsar

Explosive helium fusion may occur in the surface layer of a neutron star in a close binary system, producing a sudden increase in X-ray radiation, called a(n) ________.

X-ray burster