PHYS-116 Final Exam

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