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Test 3
Vocabulary Words
73
Astronomy
Undergraduate 1
04/05/2011

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Term
absolute magnitude
Definition

measure of an object's luminosity/

the apparent magnitude the object would have if it were located 10 parsecs away

Term
accretion disk
Definition

fast rotating disk of material that gradually falls inward as it orbits a star like object

 

(such as a white dwarf, neutron star, or black hole)

Term
apparent brightness
Definition

amount of light reaching us per unit area from a luminous object 

 

measured in watts/meters squared

Term
apparent magnitude
Definition
measure of the apparent brightness of an object/ based on the system developed by Hipparchus
Term
astrometric (visual) binary
Definition
Term
asymptotic giant
Definition

when all He is used up in the core of a star, it contracts again, leading to heating up & causing He fusion to occur in a shell above the core

 

also known as He Core Exhaustion

Term
binary star system
Definition
star system containing two stars
Term
black hole
Definition

bottomless pit in spacetime

nothing can escape from within

it is impossible to detect or observe an object that falls into one 

Term
brown dwarf
Definition

object too small to become an ordinary star

because electron degeneracy pressure stops its gravitational collapse before fusion becomes self-sustaining 

 

Term
Cepheid variable star
Definition
particularly luminous type of pulsating variable star that follows a period-luminosity relation, and therefore is very useful for measuring cosmic distances
Term
chromosphere
Definition

layer of the Sun's atmosphere below corona

most of the Sun's ultraviolet light is emitted from this region- temperature about 10,000 K

Term
convection zone
Definition

outer layer of the Sun/ region of a star in which energy is transported outward by convection

(where the energy is transported by cells of hot rising gas)

Term

convective energy transport

convective contraction on a life track?

Definition

protostar's surface temperature about 3000K

convection remains the dominant mechanism for energy transport & gravitational contraction decreases the protostar's luminosity because radius gets smaller as temperature stays constant- protostars life track drops down

Term
solar core
Definition
central region in which nuclear fusion can occur
Term
core- collapse supernova
Definition

Fe nuclei break into protons, neutrons, electrons

neutrons are formed and neutrinos are released

thermal pressure drops and core collapses until stopped by neutron degeneracy pressure

then becomes a neutron star, this only takes seconds, upper layers rebound then fly into space

 

Term
solar corona
Definition

tenuous uppermost layer of the Sun's atmosphere

most of the Sun's X Rays are emitted from this region where temperature is about 1 mil K

Term
deuterium
Definition

form of hydrogen where nucleus contains a proton and neutron- rather than only 1 proton

 

Term
eclipsing binary
Definition

binary star system in which two stars orbit the plane of our line of sight 

each star periodically eclipses the other

Term
electron degeneracy pressure
Definition
degeneracy pressure exerted by electrons in brown dwarfs and white dwarfs 
Term
event horizon 
Definition

boundary that marks the "point of no return" between a black hole and the outside universe

events that occur within the event horizon can have no influence on our observable universe

Term
evolutionary track
Definition
a path through the H-R diagram predicted by astronomers
Term
fission
Definition
one atomic nucleus breaks into two smaller nuclei, releasing energy only if the two smaller nuclei together are less massive than the original nucleus
Term
fusion
Definition
reaction where two atomic nuclei fuse together to make a single more massive nucleus, releasing energy if the final nucleus is less massive than the starting two nuclei 
Term
gamma-ray burst
Definition

sudden burst of gamma rays from deep space

coming from distant galaxies, but their precise mechanism is unknown

Term
globular (star) cluster
Definition

spherically shaped cluster of up to 1 mil stars, found primarily in the halos of galaxies

and contain only very old stars

Term
gravitational contraction
Definition
the process in which gravity causes an object to contract, converting gravitational potential energy into thermal energy
Term
gravitational equilibrium
Definition
state of balance in which the force of gravity pulling inward is counteracted by pressure pushing outward
Term
helium (triple alpha) fusion
Definition
fusion of three helium into one carbon nucleus
Term
Hertzprung-Russell diagram
Definition

graph plotting individual stars as points

stellar luminosity on the vertical axis and

spectral type (surface temp) on the horizontal

Term
hydrogen fusion
Definition

(in a high mass star) 

CNO Cycle?

Term
hydrogen shell-burning
Definition
hydrogen fusion that occurs in a shell surrounding the stellar core
Term
inverse square law (of light)
Definition

states that an object's apparent brightness depends on its actual luminosity and the inverse square of its distance from the observer

apparent brightness= 

luminosity over

4π X (distance)2

Term
luminosity
Definition

total power output of an object, usually measured in watts or LSun (units of solar luminosities)

LSun= 3.8 X 1026 watts

Term
luminosity class
Definition

category describing a region of the H-R diagram in which a star falls

I represents supergiants, III represents giants and V represents main sequence stars

II and IV are intermediate to the others

Term
Main Sequence
Definition
prominent line of points (representing main sequence stars) running from the upper left to the lower right on the H-R diagram 
Term
Main Sequence lifetime
Definition
length of time for which a star of a particular mass can shine by fusing hydrogen into helium in its core
Term
M.S. turnoff
Definition

point on a star's H-R diagram where its stars turn off from the main sequence, 

the age of the cluster is equal to the main sequence lifetime of stars at the main sequence turnoff point

Term
mass-lifetime relation
Definition
look at H-R diagram??
Term
mass-luminosity relation
Definition
look at H-R diagram??
Term
mass transfer (in a binary system)
Definition
process in which tidal forces cause matter to spill from one star to a companion star 
Term
neutrino
Definition

fundamental particle that has extremely low mass and responds only to weak force

leptons that come in three types:

electron neutrinos, mu neutrinos, tau neutrinos

Term
neutron degeneracy pressure
Definition

degeneracy pressure exerted by neutrons

as in neutron stars

Term
neutron star
Definition
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
Term
nova
Definition

dramatic heightening of a star lasting for a few weeks & then subsiding

occurs when a burst of hydrogen fusion ignites in a shell on the surface of an accreting white dwarf in a binary system

Term
open (star) cluster
Definition

up to several thousand stars 

found only in the disks of galaxies and often contain young stars

Term
parallax
Definition
apparent shifting of an object against the background due to viewing it from different positions
Term
parsec
Definition

(pc) the distance to an object with a parallax angle of 1 arcsecond

approx equal to 3.26 light years

Term
photosphere
Definition
visual surface of the Sun where temperature averages just under 6000 K
Term
planetary nebula
Definition
the glowing cloud of gas ejected from a low mass star at the end of its life
Term
proton-proton chain
Definition
chain of reactions by which low mass stars (including the Sun) fuse hydrogen into helium
Term
protostar
Definition
forming star that has not yet reached the point where sustained fusion can occur in its core
Term
pulsar
Definition
neutron star from which we see rapid pulses of radiation as it rotates
Term
pulsating variable star
Definition
stars that grow alternately brighter and dimmer as their outer layers expand and contract in size
Term
radiation zone
Definition
middle region of the Sun (between core and convection zone) where energy is transported primarily by radiative diffusion by photons
Term
radiative diffusion
Definition
process by which photons gradually migrate from a hot region (such as the solar core) to a cooler region (such as the solar surface)
Term
red giant
Definition
giant star that is red in color
Term

Roche lobe 

(binary system)

Definition
LOOK AT NOTES??
Term
Schwarzchild radius
Definition
measure of the size of the event horizon of a black hole
Term
singularity
Definition
place at the center of a black hole where gravity crushes all matter into an infinitely tiny and dense point
Term
solar activity
Definition

short lived phenomena on the Sun

including the emergence and disappearance of individual sunspots, prominences, and flares

sometimes called Solar weather

Term
solar/stellar models
Definition
NOTES!!??
Term
solar neutrino problem
Definition
disagreement between the predicted and observed number of neutrinos coming from the Sun
Term
solar wind
Definition
stream of charged particles ejected from the Sun
Term
spectral type
Definition

way of classifying a star by the lines appearing on its spectrum- related to surface temperature

basic spectral types designated by OBAFGKM

O for the hottest stars and M for the coolest

all letters are subdivided by numbers 0 to 9

Term
spectroscopic binary
Definition
binary system whose binary nature is revealed because we detect the lines of one or both stars alternatively becoming blue shifted and redshifted as the stars orbit each other
Term
sunspot
Definition
blotches on the surface of the Sun that appear darker than surrounding regions
Term
supergiant
Definition
very large & very bright stars of luminosity class I that appear at the top of an H-R diagram
Term
supernova
Definition
explosion of a star
Term
supernova remnant
Definition
glowing expanding cloud of debris coming from a supernova explosion
Term
white dwarf
Definition
hot compact corpses of low mass stars, typically with a mass similar to that of the Sun compressed into a volume the size of Earth
Term
white dwarf supernova
Definition
supernova that occurs when an accreting white dwarf reaches the white dwarf limit, then ignites runaway carbon fusion, and explodes like a bomb often called a Type Ia supernova
Term
X-ray binary star system
Definition
binary star system that emits substantial amounts of X rays & thought to be from an accretion disk around a neutron star or black hole
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