Chapter 19: Stars (Definitions)

Front 1

Universe

Back 1

Everything that exists in time and space :)

Front 2

Protostar

Back 2

A very hot, very dense sphere of condensing dust and gas that's on its way to becoming a star.

Front 3

Nuclear fusion

Back 3

A process where two smaller nuclei join to form one giant nucleus.

Front 4

Radiation pressure

Back 4

Pressure from the photons in the core of a star, which acts outwards to counteract pressure from gravitational force, pulling the matter inwards.

Front 5

Gas pressure

Back 5

The pressure of nuclei in the star's core pushing outwards and contracting the gravitational force pulling matter inwards.

Front 6

Main Sequence

Back 6

The main period on a HR diagram in a stars life, during which is is most stable.

Front 7

Planet

Back 7

An object in orbit around a star with
-a mass large enough for its own gravity to give it a round shape

-undergoes no fusion reactions

-has cleared its orbit of most other things

Front 8

Planetary satellite

Back 8

A body in orbit around a planet, natural or artificial.

Front 9

Comets

Back 9

A small irregular body made of ice, dust and small pieces of rock in an elliptical orbit around the sun.

Front 10

Solar System

Back 10

A planetary system consisting of a star and at least one planet in orbit around it.

Front 11

Galaxies

Back 11

A collection of stars and interstellar dust and gas bound together by their mutual gravitational force.

Front 12

Red giant

Back 12

An expanding star at the end of its life with an inert core in which fusion no longer takes place, but in which fusion of lighter elements continues in the shell around the core.

Front 13

White dwarf

Back 13

A very dense star formed from the core of a red giant, in which no fusion occours

Front 14

Electron degeneracy pressure

Back 14

A quantum-mechanical pressure created by the electrons in the core of a star due to the pauli-exclusion principle.

Front 15

Chandra-sekhar limit

Back 15

(1.44 solar masses)
The maximum mass of a star's core where the electron degeneracy pressure is enough to prevent gravitational collapse.

Front 16

Red super giant

Back 16

A huge star in the last stages of its life before it explodes in a supernova.

Front 17

Neutron star

Back 17

The remnant core of a massive star after it has gone supernova and the core has collapsed so far that in order to escape and object would need an escape velocity greater that the speed of light. (therefore nothing can escape)

Front 18

Supernova

Back 18

The implosion of a red super giant at the end of its life, which leads to subsequent ejection of stellar matter into space, leaving an inert remnant core.

Front 19

Hertzsprung Russell diagram

Back 19

A graph showing the relationship between the luminosity of stars in our galaxy (y-axis) and their average surface temperature (x-axis) with temperature increasing right to left.

Front 20

Luminosity

Back 20

The total radiant power output of a star.

Front 21

Energy levels

Back 21

A discrete amount of energy that an electron within an atom is permitted to posses

Front 22

Ground state

Back 22

The energy level with the most negative value possible for an electron within an atom - the most stable energy state of an electron

Front 23

Excited ;)

Back 23

(an atom) Containing an electron or electrons that have absorbed energy and have been boosted into a higher energy level