Astronomy Chapters 12-16

Front 1

Low-mass stars

Back 1

Stars born with masses less than about 2M Sun; these stars end their lives by ejecting a planetary nebula and becoming a white dwarf.

Front 2

High-mass stars

Back 2

Stars born with masses above about 8M Sun; these stars will end heir lives by exploding as supernovae

Front 3

Molecular Clouds

Back 3

Cool, dense interstellar clouds in which the low temperatures allow hydrogen atoms to pair up into hydrogen molecules.

Front 4

Protostar

Back 4

A forming star that has not yet reached the point where sustained fusion can occur in its core.

Front 5

Life Track

Back 5

A track drawn on an H-R diagram to represent the changes in a star's surface temperature and luminosity during its life; also called an evolutionary track.

Front 6

Main Sequence Star

Back 6

Stars whose temperature and luminosity place them on the main sequence of the H-R diagram. Main-sequence stars are all releasing energy by fusing hydrogen into helium in their cores.

Front 7

Red Giant

Back 7

A giant star that is red in color

Front 8

Hydrogen-shell burning

Back 8

Hydrogen fusion that occurs in a shell surrounding a stellar core.

Front 9

Helium Fusion

Back 9

The fusion of three helium nuclei into one carbon nucleus.

Front 10

Helium Flash

Back 10

The event that marks the sudden onset of helium fusion in the previously inert helium core of a low-mass star.

Front 11

Planetary Nebula

Back 11

The glowing cloud of gass ejected from a low-mass star at the end of its life.

Front 12

Supernova

Back 12

The explosion of a star

Front 13

The nearest supernova seen in nearly 400 years and helped astronomers refine theories of supernovae

Back 13

Supernova 1987A

Front 14

Supernova Remnants

Back 14

A glowing, expanding cloud of debris from a supernova explosion.

Front 15

White dwarfs

Back 15

The hot, compact corpses of low-mass stars, typically with a mass similar to the Sum compressed to a colume the size of the Earth.

Front 16

Chandrasekhar Limit

Back 16

The maximum possible mass for a white dwarf, which is about 1.4M Sun

Front 17

Accretion Disk

Back 17

A rapidly rotating disk o material that gradually falls inward as it orbits a starlike object.

Front 18

Nova

Back 18

The dramatic brightening of a star that lasts for a few weeks and then subsides; occurs when a burst of hydrogen fusion ignites in a shell on the surface of an accreting white dwarf in a binary star system.

Front 19

White Dwarf Supernova

Back 19

A supernova that occurs when an accreting white dwarf reaches the white-dwarf limit, ignites runaway carbon fusion, and explodes like a bomb.

Front 20

Massive Star Supernova

Back 20

A supernova that occurs when a massive star dies, initiated by the catastrophic collapse of its iron core.

Front 21

Neutron Stars

Back 21

The compact corpse of a high-mass star left over after a supernova; typically contains a mass comparable to the mass of the Sun in a volume just a few kilometers in radius.

Front 22

Pulsars

Back 22

A neutron star from which we see rapid pulses of radiation as it rotates.

Front 23

Blackhole

Back 23

A bottomless pit in spacetime. Nothing can escape from within a black hole, and we can never again detect or observe an object that falls into a black hole.

Front 24

Disk

Back 24

The portion of the spiral galaxy that looks like a disk and contains an interstellar medium with cool gas and dust; stars of many ages are found here.

Front 25

Bulge

Back 25

The central portion of a spiral galazy that is roughly spherical (or football shaped) and bulges above and below the plane of the galactic disk.

Front 26

Spiral Arms

Back 26

The bright, prominent arms, usually in a spiral pattern, found in most spiral galaxies.

Front 27

Halo

Back 27

The spherical region surrounding the disk of a spiral galaxy.

Front 28

Globular Clusters

Back 28

A spherically shaped cluster of up to a million or more stars; globular clusters are found primarily in the halos of galaxies and contain only very old stars.

Front 29

Dark Matter

Back 29

Matter that we infer to exist from its gravitational effects but from which we have not detected any light; dark mater apparently dominates the total mass of the universe.

Front 30

Our sun is located in the disk about 28,000 light-years from the galactic center-a little more than halfway out from the center to the edge of the disk.

Back 30

The Suns location in the Milky Way

Front 31

Spiral Galaxies

Back 31

Galaxies like the Milky Way with arching structures lying in a plane and emanating from the nuclear bulge.

Front 32

Barred Spiral Galaxies

Back 32

Galaxies with a bar of stars running through the nuclear bulge

Front 33

Elliptical Galaxies

Back 33

Galaxies with an elliptical shape, no spiral arms, and little interstellar matter.

Front 34

Irregular Galaxies

Back 34

Galaxies that are asymmetrical and are sometimes just 2 or more galaxies colliding.

Front 35

Hubble's Law

Back 35

A linear relationship between the recessional velocity and the distance to the galaxies. V=HD

Front 36

Big-Bang theory

Back 36

States that all the matter in our observable universe came into being at a single moment in time as an extremely hot, dense mixture of subatomic particles and radiation.

Front 37

Lookback time

Back 37

Refers to the amount of time since the light we see from a distant object was emitted.

Front 38

Cosmological Horizon

Back 38

Marks the limits of the observable universe; a boundary int time, not space.

Front 39

Messier Catalogue

Back 39

1st catalog of nonstellar "fuzzy" objects during the 1770's. 109 such objects.

Front 40

Nucleosynthesis

Back 40

When helium is depleted, the fusion of heavier elements begins in High-Mass Stars.