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blackbody
ideal absorber
total black at decreased temperature than surroundings
blackbody curves
The curve obtained when the intensity of radiation from a blackbody at a particular temperature is plotted against wavelength.
Wien's law
The higher the temperature of a body the shorter the wavelength of it's maximum radiation. (hotter = shorter wavelength)
Stefan-Boltzmann Law
The relationship stating that an object emits energy at a rate proportional to the fourth power of its temperature, in Kelvins.
energy flux
the amount of energy passing through a unit area (for example, 1 square meter) per second; the units of flux are watts per square meter
luminosity
the true brightness of an object
Planck's Law
a relationship between the energy carried by a photon and its wavelength
absorption lines
a set of dark lines that show frequencies at which light has been absorbed from a star's bright spectrum
spectroscope
An instrument that separates light into a spectrum.
emission lines
lines that are made when certain wavelengths of light, or colors, are given off by hot gases
spectral analysis
method of charting and analyzing the chemical properties of matter by looking at the bands in their visible spectrum of light
element
A pure substance made of only one kind of atom
periodic table
A chart of the elements showing the repeating pattern of their properties
spectrograph
An instrument that separates light into colors and makes an image of the resulting spectrum.
diffraction grating
a device made of thousands of closely spaced slits through which light is passed in order to produce a spectrum
Kirchhoff's Laws
the sum of current flowing into a junction must equal the sum of the current leaving at any junction
the sum of voltage sources = the sum of voltage drops around a closed-circuit loop
continuous spectrum
the emission of a continuous range of frequencies of electromagnetic radiation
emission line spectrum
a diagram or graph that indicates the degree to which a substance emits radiant energy with respect to wavelength
absorption line spectrum
A cloud of gas between us and a light bulb can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum.
atom
Basic unit of matter
electromagnetic force
a force associated with charged particles, which has two aspects, electric force and magnetic force
strong nuclear force
the powerful attractive force that binds protons and neutrons together in the nucleus
weak nuclear force
a powerful attractive force that acts over a short range
isotope
Atoms of the same element that have different numbers of neutrons
ion
A charged atom
Ionization
any process that results in the formation of an ion
molecules
Groups of two or more atoms held together by chemical bonds
quantum mechanics
behavior of submicroscopic particles
transition
a change from one state or condition to another
ground state
The lowest energy state of an atom
excited state
A state in which an atom has a higher potential energy than it has in its ground state
blueshift
A Doppler shift in which spectral features are shifted to shorter wavelengths, observed when an object is moving toward the observer.
redshift
shift of light to a longer wavelength as it moves away
doppler shift
the shift to a different wavelength
radial velocity
motion toward or away from the observer; the component of relative velocity that lies in the line of sight
transverse velocity
The portion of an object's velocity perpendicular to our line of sight to it.
proper motion
the angular change per year in the direction of a star as seen from the Sun
stellar evolution
the changes in size, luminosity, temperature, and chemical composition that occur as a star ages
stellar parallax
the apparent shift in the position of a nearby star (relative to distant objects) that occurs as we view the star from different positions in Earth's orbit of the Sun each year
apparent magnitude
the brightness of a star as seen from Earth
absolute magnitude
The actual brightness of a star
inverse-square law
the intensity of radiation is inversely proportional to the square of the distance from the source of radiation
photometry
The art of measuring the intensity of light.
stellar spectroscopy
the study of the properties of stars encoded in their spectra
spectral types
a classification of stars according to the appearance of their spectra
OBAFGKM sequence
The sequence of stellar spectral classifications from hottest to coolest stars.
Hertzsprung-Russell diagrams
A graph plotting individual stars as points, with stellar luminosity on the vertical axis and spectral type (or surface temperature) on the horizontal axis.
main-sequence
a diagonal area on an H-R diagram that includes more than 90 percent of all stars
main-sequence star
A normal star that is undergoing nuclear fusion of hydrogen into helium. Our sun is a typical main sequence star.
giant stars
stars that have diameters 10-100 times as large as the sun
red giants
Huge stars that are cooler than the Sun, emit much more light than a sun like star, form when a star starts to run out of helium, appear to be very bright
supergiants
The most luminous, most massive stars, with diameters greater than 100 times the diameter of the sun.
white dwarfs
very small, very hot stars
luminosity classes
I supergiants
II Bright giants
III giants
IV sub-giants
V main sequence
spectroscopic parallax
The method of determining a star's distance by comparing its apparent magnitude with its absolute magnitude, as estimated from its spectrum.
optical doubles
two stars that have a small angular separation as seen from Earth but are not gravitationally linked
binary stars
Star systems that have two stars
center of mass
the point in an object that moves as if all the object's mass were concentrated at that point
visual binaries
can see the two stars and used to get masses
eclipsing binaries
two stars that block each others light, easy to measure masses of stars
light curves
graphs that show how an object's intensity varies with time
close binary
a binary star system in which the two stars are very close together
mass-luminosity relation
the more massive a star is, the more luminous it is
spectroscopic binaries
a binary-star system which appears as a single star from Earth, but whose spectral lines show back-and-forth Doppler shifts as two stars orbit one another
radial-velocity curve
a plot showing the variation of radial velocity with time for a binary star or variable star
initial mass function
The numbers of stars on the main sequence at all different masses
interstellar medium
The gas and dust that exists in open space between the stars.
reflection nebula
interstellar dust that is visible due to reflected light from a nearby star. Bluish in color due to the reflected light.
nebula
A large cloud of dust and gas in space
molecular clouds
cool, dense interstellar clouds in which the low temperatures allow hydrogen atoms to pair up into hydrogen molecules
giant molecular clouds
large, cold interstellar clouds with diameters of dozens of light-years and typical masses of 105 solar masses; found in the spiral arms of galaxies, these clouds are where stars form
dark nebulae
a cloud of interstellar gas and dust that obscures the light of more distant stars
emission nebulae
glowing gas clouds, often red in appearance because of scattered red light from hydrogen atoms
interstellar extinction
the dimming of starlight as it passes through the interstellar medium
interstellar reddening
the process in which dust scatters blue light out of starlight and makes the stars look redder
Jeans unstable
Any volume of gas and dust that meets the conditions of a Jeans instability and hence will collapse under the influence of its own gravitational force
supernova remnants
The shredded remains of a more-massive star (several times more massive than the Sun). Left behind at the centers of these might be a neutron star (or a pulsar, a special kind of neutron star), or a black hole. Tend to have a more "exploded" and fragmented appearance, not "smooth" like Planetary Nebulae.
Bok globules
named after astronomer Bart Bok who studied them extensively, are small dark clouds made of gas and dust that are typically condensing to form a star or stars.
open clusters
Loose, disorganized appearance and contain no more than a few thousand stars
protostar
A contracting cloud of gas and dust with enough mass to form a star
pre-main-sequence star
the stage of star formation just before the main sequence; it involves slow contraction of the young star
evolutionary track
a representation of the changes in color and luminosity of an evolving star
birth line
In the H-R diagram, the line above the main sequence where protostars first become visible
T Tauri stars
young, variable pre-main-sequence stars associated with interstellar matter that show erratic changes in luminosity
H II regions
the region of ionized hydrogen in interstellar space
OB association
an unbound group of very young, massive stars predominantly of spectral types O and B
zero-age main sequence (ZAMS)
The location in the H-R diagram where stars first reach stability as hydrogen-burning stars
red dwarfs
(cool, faint, and small) on lower right
hydrogen shell fusion
hydrogen fusion that occurs in a shell surrounding a stellar core
Pauli exclusion principle
An atomic orbital may describe at most two electrons, each with opposite spin direction
electron degeneracy pressure
degeneracy pressure exerted by electrons, as in brown dwarfs and white dwarfs
core helium fusion
the fusion of helium to form carbon and oxygen at the center of a star
helium flash
the event that marks the sudden onset of helium fusion in the previously inert helium core of a low-mass star
instability strip
A location on an H-R diagram where evolving stars pulsate.
variable stars
stars that regularly or repeatedly change in magnitude
RR Lyrae variables
Stars with pulsation periods ranging from 1.5 hours to 1 day, generally having the same luminosity, regardless of pulsation period length.
Cepheid variable
A star whose brightness varies periodically because it expands and contracts; a type of pulsating star.
Type I Cepheids
brighter, more massive, metal rich stars