Astronomy Chapter 9

Front 1

Interstellar medium

Back 1

The dust and gas distrubuted between the stars

Front 2

Nebula

Back 2

A glowing or dark cloud of gas or a cloid of dust reflecting the light of nearby stars

Front 3

Interstellar reddening

Back 3

The process in which dist scatters blue light out of starlight and makes stars look redder

Front 4

Interstellar dust

Back 4

Microscopic solid grains in the interstellar medium

Front 5

Emission nebula

Back 5

A cloud of glowing gas excited by ultraviolet radiation from hot stars

Front 6

HIII region

Back 6

A refion of ionized hydrogen around a hot star

Front 7

Reflection nebula

Back 7

A nebula produced by starlight reflecting off dust particles in the interstellar medium

Front 8

Dark nebula

Back 8

A cloud of gas and dust of any size seen silhouetted against a brighter nebula

Front 9

Molecular cloud

Back 9

A dense interslettar gas cloud im which atoms are able to link together to form molecules such as H2 and CO

Front 10

Interstellar emission lines

Back 10

A bright spectral line produced by excited intertellar gas viewed against a dark, cold background

Front 11

Shock wave

Back 11

A sudden change in pressure that travels as an intense sound wave

Front 12

Association

Back 12

Group of widely scattered stars (10 to 1,000) moving together through space

Front 13

Protostar

Back 13

A collapsing cloud of gas and dust destined to become a star

Front 14

Protostellar disk

Back 14

A gas cloud around a forming star flattened by its rotation

Front 15

Birth line

Back 15

In the H-R diagram, thr linr aboce the main sequence where protostars first become visible

Front 16

CNO cycle

Back 16

A series of nuclear reactions that use carbon as a catalyst to combine four hydrogen atoms to make one helium atom plus energy

Front 17

T-Tauri star

Back 17

A young star surrounded by gas and dust, believed to be contracting toward the main sequence

Front 18

Bok globule

Back 18

Small dark cloud only about 1 ly in diameter that co tains 10 to 1,000 solar masses of gas and dust

Front 19

Herbig-Haro object

Back 19

A small nebula that varies irregularly in brightness, believed to be associated with star formation

Front 20

Bipolar flow

Back 20

Jets of gas flowing away from a central object in opposite directions; usually applied to protostars

Front 21

Triple-alpha process

Back 21

The nuclear fusion process that comvines three helium nuclei to make one carbon nucleus

Front 22

Hydrostatic equilibrium

Back 22

The balance between the weight of the material pressing downward on a layer in a star and the pressure in that layer

Front 23

Energy transport

Back 23

Flow of energy from hot regions to cooler regions by one of three methods: conduction, convection, or radiation

Front 24

Opacity

Back 24

The resistance of a gas to the passage of radiation

Front 25

Stellar model

Back 25

A table of numbers representing the conditions in various layers within a star

Front 26

Brown dwarf

Back 26

A star whose mass is too low to ignite nuclear fusion

Front 27

Zero-age main sequence

Back 27

The location in the H-R diagram where stars first reach stability as hydrogen-burning stars

Front 28

Pressure-temperature thermostat

Back 28

The relation between gas pressure ans temperature, the stability of a star depends upon this

Front 29

The wavelength region of the electromagnetic spectrum in which protostars are observable is the

Back 29

Infrared

Front 30

Interstellar dust makes up roughly ______ percent of the mass of the interstellar medium

Back 30

1

Front 31

Emmission nebulae are produced when a hot star excites the gas near it to produce an emission spectrum. To do this, the star must be hotter than ______ K

Back 31

25000

Front 32

On the H-R diagram, protostars remain hidden in vidible wavelengths until they cross the

Back 32

Birth line

Front 33

Main-sewuence stars that produce energy through the CNO cylce are the _______ massive

Back 33

Most

Front 34

When powerful jets from a newborn star strike the interstellar medium, they produce

Back 34

Herbig-Haro objects

Front 35

Stars that fluctuate in brightness and appear to be newborn stars just blowing away their dust cocoons are known as

Back 35

T-Tauri

Front 36

Reflection nebule appear to be what color?

Back 36

Blue

Front 37

Stars that co tract the slowest to land on the zero-age main sewuence line on the H-R diagram

Back 37

Are the least massive

Front 38

To begin to collapse into stars, amd interatellar cloud must be

Back 38

Cold and dense

Front 39

Starlight passing through interstellar dust becomes

Back 39

Fainter and redder

Front 40

Main sequence stars of which spectral class use the CNO cycle?

Back 40

A

Front 41

Bok globules contain

Back 41

10-1000 solar masses

Front 42

Which of the following is not one of the four laws of stellar structure?

Back 42

Conservation of charge

Front 43

If an object formed from a cloud of dust and gas is less than 0.08 solar masses, it forms a

Back 43

Brown dwarf

Front 44

The major gas component in the interstellar medium is

Back 44

Hydrogen

Front 45

What two characteristics are balanced in hydrostatic equilibrium?

Back 45

Weight and pressure

Front 46

When a star begins its stable life it begins on the

Back 46

Zero-age main sequence

Front 47

The average star spends ____ of its life on the main sequence

Back 47

90%