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Luminosity

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a measure of the light energy emitted into space by stars per second For stars, the Sun is of average luminosity. For the most part, very dim stars are most common, stars of medium L like the sun are fairly common, and highly luminous stars are very rare.

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Luminosity Function

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graph that describes how for stars, the Sun is of average luminosity. For the most part, very dim stars are most common, stars of medium L like the sun are fairly common, and highly luminous stars are very rare.

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Space Velocity "V"

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the speed and direction a star is moving through space

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Tangential Velocity - "Vt" -

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the component of a star's velocity that is traveling across the sky plane, OR more importantly perpendicular to our line of sight

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Radial Velocity -"Vr" -

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the component of a star's velocity that is traveling parallel to our line of sight, measured from Doppler shifts of the star's spectral lines If a star is approaching us, the wavelength decreases (blue shift) If a star is moving away from us, the wavelength increases (red shift)

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Proper Motion

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the number of arcseconds that a star appears to move per year on the celestial sphere

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Parallax

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the apparent displacement of an object caused by the actual change in position of the observer, also the go-to way to measure the distance of the stars. *The closer the object you are viewing, the greater apparent parallax shift*. Most stars in the universe are too far away to accurately measure the angle of apparent shift Parallax only works for stars that are relatively nearby, and the majority of stars in our galaxy are much too far away to exhibit any apparent shift in position as Earth orbits the Sun.

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Stellar parallax

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the apparent movement of a nearby star against a background of infinite stars that occurs due to the change in direction from the earth to the star as the Earth orbits the Sun.

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Parallax Angle

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angle formed by the apparent shift in stellar parallax Parallax angles are smallest for the most distant stars, so if a parallax angle was measured to be too small then the astronomer would assume the star is farther away than it actually is

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Equation for Parallax

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D = 1/p D =distance in parsecs, p = parallax angle in arcseconds

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Hipparcos

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High Precision Parallax Collecting Satellite Satellite created by the European Space Agency that measures parallax angles with an accuracy of up to .001 arcseconds

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*If a star's distance can be known its luminosity can be determined from its apparent brightness*

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*If a star's distance can be known its luminosity can be determined from its apparent brightness*

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Brightness (b)

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the amount of energy that passes each second through a square meter of a spherical celestial object's surface area. Expressed as Watts of power.

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Apparent Brightness

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same exact thing as brightness.

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Concept of Brightness

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if you have a star with a brightness of 1000 watts, 1 square meter of a solar panel receives 1000 watts of power from that star

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Inverse Square Law

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Law of science that describes the inverse relationship between the apparent brightness of a star and the square of its distances. For example, if the distance between an observer and a star doubles, that is increase by 2 x, the apparent brightness decreases by a factor of 4 (radiation spread over an area that is 4 times larger); If you increase the distance by 3 times your brightness decreases by a factor of 9; 4, 16; 5, 25; you get the idea Relates a star's luminosity, distance, and apparent brightness to the corresponding quantities for the Sun Based on this relationship, we are able to determine the luminosity of a star by comparing the distance of that star and the brightness of that star to the distance of earth to the sun and the apparent brightness of the sun. A very nearby flashlight will appear much brighter than a very distant spotlight. Although a large spotlight will emit more light, the light that appears brighter depends on their distances away

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Photometry

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the process by which scientists measure the apparent brightness of the stars

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Apparent Magnitude (brightness)

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A measure of a star's apparent brightness as seen from Earth

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Absolute Magnitude (Luminosity)

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A true measure of a star's energy output - The apparent magnitude a star would have if it were located exactly 10 parsecs from earth The Sun's absolute magnitude is 14.8

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Distance Modulus

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The difference between apparent magnitude (m) and absolute magnitude (M). *= m-M* The greater the value for distance modulus, the greater distance that star is from earth. Large discrepancies in absolute and apparent tend to mean the star is comparatively very far from earth

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A Star's color depends on its surface temperature

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The intensity of light from a relatively cool star peaks at long wavelengths, making the star look red. The intensity of light from a relative hot star peaks at short wavelengths, making it look blue. The shorter the peak wavelength, the higher the temperature, and the higher the frequency. Blue is always hotter than red Red stars are relatively cold, with low surface temps; Blue stars are relatively hot, with high surface temps

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UBV Photometry

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Photometry technique that utilizes the U, B, and V filters in a telescope that are transparent to UV rays, Blue Rays, and Yellow-Green rays respectively.

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Color Ratios

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ratio that compares the brightness of stars across the UBV filter, set up as Bv/Bb and Bb/Bu. The higher the surface temp, the lower the ratio for both sets.

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The Spectra of stars reveal their chemical composition as well as their surface temperatures

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-The process and technique in which scientists analyze the light spectrum of an individual star to determine many of that star's properties is called spectroscopy -Absorption lines are created when the light flows outward through the upper layers of the star's atmosphere -Atoms absorb wavelengths of the radiation at specific levels depending on the specific atom present (hydrogen, helium, etc) and the pattern of each atom's spectral lines serve as the comparison for new observations (though they vary a lot) -Due to the large amount of spectra that comes form the stars, similar looking stellar spectra are placed into spectral classes (OBAFGKM; each letter representing a different class) - O is most similar to B, B is more similar to F than it is to G -Within a particular spectral class, the larger numbers correspond to cooler stars. For example, a G2 star is hotter than a G8 star because a G2 star is closer to the hotter F-spectral class in the sequence OBAFGKM -*For a given luminosity, the greater the surface temperature, the smaller the radius will be. -*For a given surface temperature, the greater the luminosity the larger the radius must be

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Hertzsprung-Russell (H-R) Diagrams

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A simple yet important graph that plots the luminosities of stars (or their absolute magnitude) against their spectral types (or surface temperatures). - increasing luminosity on the vertical axis and increasing temperature on the horizontal axis. The data points are grouped into a few regions throughout the graph showing that luminosity and surface temperature are correlated Most stars cluster around the red curve called the main sequence Makes sense if we remember that the majority of stars have comparatively cooler surface temperatures For a given Stellar Radius: As the surface temperature increases, the star glows more intensely and the luminosity of that star increases As the surface temperature decreases, the star will glow less with a much smaller luminosity Structure: As you move to the left of the graph, surface temperature increases As you move up the graph on the y axis, luminosity increases

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Star Varieties (Referring to the Hertzsprung-Russell (H-R) Diagrams): MAIN SEQUENCE

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This variety accounts for the majority of stars (about 90%) Span from the top left of the HR graph to the bottom right Gain their energy through the conversion of hydrogen to helium in their cores The Sun is a main sequence star Stars like our Sun derive their energy from nuclear reactions in the core, whereas a brown dwarf derives its energy from gravitational contraction.

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Star Varieties (Referring to the Hertzsprung-Russell (H-R) Diagrams): GIANTS

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Upper right hand corner of the HR graph; are Luminous and Cool Since they are cool, they are much less bright (emit less energy). So, in order for these cool stars to be so luminous, they must be incredibly large (Giants) 10 - 100x larger than our Sun. Between 3000 and 6000K surface Temperature The cooler giants (3000-4000K) are called Red Giants as they appear red

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Super-Giants

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Rare stars that are bigger and brighter than red giants with radii of up to 1000x that of our Sun Together, giants and super-giants make up about 1% of the stars in the sky

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White Dwarfs

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located in the lower left hand corner of the HR diagram This means they are extremely hot, but also have very low luminosity, meaning they must be very small aka dwarfs About the same size as earth No thermonuclear reactions occur in their cores Glowing remnants of what used to be giant stars

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Brown Dwarfs

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lower right hand side of the HR diagram Cool with low luminosity Never will become stars, not massive enough for significant fusing of hydrogen in their core Gets energy from gravitational contraction, not a true star

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Details of a star's spectrum reveal whether it is a giant, a white dwarf, or a main sequence star

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The differences between the spectra of stars of different luminosity are due to differences between the stars' atmospheres which is where absorption lines are produced. The higher the density and pressure, the more hydrogen collision, the broader the hydrogen spectral lines are Typically, the smaller the star (comparatively), the higher the density and pressure is, meaning broad and clear absorption lines Luminosity broken down into 5 classes I - V. The higher the class, the lower the average luminosity for a given surface temperature If 2 stars have identical surface temperatures, but 1 has a much larger luminosity, you can assume that that star must be of a much more massive size to emit its higher levels of luminosity.

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Spectroscopic Parallax

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The method for determining the distance of a star using its spectral class, luminosity class, and location of the H-R diagram Deduce using the formula for the relationship between luminosity, distance, and apparent brightness No actual parallax involved, just similar because it answers a question of distance Helpful to make claims about stars that are simply too far to observe true parallax. H-R diagram plays a big role in determining the luminosity of a star from its spectral type and luminosity class Can then deduce property of distance from that information Key Formulas: L = 4pid^2b L = 4piR^2T^4

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Binary Stars

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Stars that orbit each other because of their mutual gravitational attraction Helps us determine the weight of these stars using Kepler's 3rd law Visual Binaries - Binary pairing that you can actually see orbiting each other Have extremely long orbital periods

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Center of Mass

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the center of the elliptical orbit of binary stars; a completely imaginary point that lies along a line connecting the 2 stars The center of mass in a binary star system is always nearer to the more massive star The two stars are always on opposite ends of the center of mass, so they never collide If two stars orbiting a common center of mass were moved farther apart, their masses would not change, but the period would increase following Kepler's 3rd law

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22-year solar cycle

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The semiregular 22-year interval between successive appearances of sunspots at the same latitude and with the same magnetic polarity

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chromosphere

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A layer in the atmosphere of the Sun between the photosphere and the corona

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CNO cycle

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A series of nuclear reactions in which carbon is used as a catalyst to transform hydrogen into helium

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conduction

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The transfer of heat by directly passing energy from atom to atom

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convection

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The transfer of energy by moving currents of fluid or gas containing that energy

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convective zone

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The region in a star where convection is the dominant means of energy transport

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corona

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The Sun's outer atmosphere, which has a high temperature and a low density

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coronal hole

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A region in the Sun's corona that is deficient in hot gases

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coronal mass ejection

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An event in which billions of tons of gas from the Sun's corona is suddenly blasted into space at high speed

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differential rotation

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The rotation of a nonrigid object in which parts adjacent to each other at a given time do not always stay close together

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filament

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A portion of the Sun's chromosphere that arches to high altitudes

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granulation

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The rice grain-like structure found in the solar photosphere

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granule

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A convective cell in the solar photosphere

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helioseismology

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The study of the vibrations of the Sun as a whole

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hydrogen fusion

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The thermonuclear conversion of hydrogen into helium

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hydrostatic equilibrium

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A balance between the weight of a layer in a star and the pressure that supports it

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limb darkening

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The phenomenon whereby the Sun looks darker near its apparent edge, or limb, than near the center of its disk

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luminosity (of the Sun)

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The rate at which electromagnetic radiation is emitted from a star or other object

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magnetic reconnection

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An event where two oppositely directed magnetic fields approach and cancel, thus releasing energy

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magnetic-dynamo model

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A theory that explains the solar cycle as a result of the Sun's differential rotation acting on the Sun's magnetic field

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magnetogram

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An image of the Sun that shows regions of different magnetic polarity

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negative hydrogen ion

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A hydrogen atom that has acquired a second electron

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neutrino

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A subatomic particle with no electric charge and very little mass, yet one that is important in many nuclear reactions

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neutrino oscillation

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The spontaneous transformation of one type of neutrino into another type

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photosphere

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The region in the solar atmosphere from which most of the visible light escapes into space

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plage

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A bright region in the solar atmosphere as observed in the monochromatic light of a spectral line

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plasma

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A hot ionized gas

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positron

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An electron with a positive rather than negative electric charge; the antiparticle of the electron

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prominence

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Flamelike protrusions seen near the limb of the Sun and extending into the solar corona

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proton-proton chain

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A sequence of thermonuclear reactions by which hydrogen nuclei are built up into helium nuclei

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radiative diffusion

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The random migration of photons from a star's center toward its surface

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radiative zone

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A region within a star where radiative diffusion is the dominant mode of energy transport

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solar flare

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A sudden, temporary outburst of light from an extended region of the solar surface

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solar neutrino

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A neutrino emitted from the core of the Sun

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solar neutrino problem

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The discrepancy between the predicted and observed numbers of solar neutrinos

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solar wind

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An outward flow of particles (mostly electrons and protons) from the Sun

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space weather

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Variations in the solar wind and magnetic field, which can affect satellites and astronauts

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spicule

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A narrow jet of rising gas in the solar chromosphere

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sunspot

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A temporary cool region in the solar photosphere

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sunspot cycle

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The semiregular 11-year period with which the number of sunspots fluctuates

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sunspot maximum

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That time during the sunspot cycle when the number of sunspots is highest

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sunspot minimum

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That time during the sunspot cycle when the number of sunspots is lowest

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supergranule

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A large convective feature in the solar atmosphere, usually outlined by spicules

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thermal equilibrium

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A balance between the input and outflow of heat in a system

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thermonuclear fusion

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The combining of nuclei under conditions of high temperature in a process that releases substantial energy

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Zeeman effect

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A splitting or broadening of spectral lines due to a magnetic field

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absolute magnitude

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The apparent magnitude that a star would have if it were at a distance of 10 parsecs

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apparent brightness

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The flux of a star's light arriving at Earth

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apparent magnitude

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A measure of the brightness of light from a star or other object as measured from Earth

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binary star

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Two stars orbiting each other

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brown dwarf

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A starlike object that is not massive enough to sustain hydrogen fusion in its core

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center of mass

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The point between a star and a planet, or between two stars, around which both objects orbit

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color ratio

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The ratio of the apparent brightness of a star measured in one spectral region to its brightness measured in a different region

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distance modulus

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The difference between the apparent and absolute magnitudes of an object

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double star

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A pair of stars located at nearly the same position in the night sky. Some, but not all, double stars are binary stars

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eclipsing binary

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A binary star system in which, as seen from Earth, stars periodically pass in front of each other

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giant

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A star whose diameter is typically 10 to 100 times that of the Sun and whose luminosity is roughly that of 100 Suns

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Hertzsprung-Russell diagram (H-R diagram)

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A plot of the luminosity (or absolute magnitude) of stars against their surface temperature (or spectral type)

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inverse-square law

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The statement that the apparent brightness of a light source varies inversely with the square of the distance from the source

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light curve

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A graph that displays how the brightness of a star or other astronomical object varies over time

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luminosity

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The rate at which electromagnetic radiation is emitted from a star or other object

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luminosity class

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A classification of a star of a given spectral type according to its luminosity

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luminosity function

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The numbers of stars of differing brightness per cubic parsec

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magnitude scale

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A system for denoting the brightnesses of astronomical objects

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main sequence

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A grouping of stars on the Hertzsprung-Russell diagram extending diagonally across the graph from hot, luminous stars to cool, dim stars

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main-sequence star

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A star whose luminosity and surface temperature place it on the main sequence on an H-R diagram; a star that derives its energy from core hydrogen fusion

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mass-luminosity relation

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A relationship between the masses and luminosities of main-sequence stars

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metals

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In reference to stars and galaxies, any element other than hydrogen and helium; in reference to planets, a material such as iron, silver, and aluminum that is a good conductor of electricity and of heat

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OBAFGKM

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The temperature sequence (from hot to cold) of spectral classes

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optical double star

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Two stars that lie along nearly the same line of sight but are actually at very different distances from us

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parallax

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The apparent displacement of an object due to the motion of the observer

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parsec

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A unit of distance; 3.26 light-years

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photometry

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The measurement of light intensities

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proper motion

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The angular rate of change in the location of a star on the celestial sphere, usually expressed in arcseconds per year

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radial velocity

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That portion of an object's velocity parallel to the line of sight

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radial velocity curve

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A plot showing the variation of radial velocity with time for a binary star or variable star

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red giant

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A large, cool star of high luminosity

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space velocity

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The speed and direction in which a star moves through space

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spectral classes

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A classification of stars according to the appearance of their spectra

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spectral type

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A subdivision of a spectral class

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spectroscopic binary

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A binary star system whose binary nature is deduced from the periodic Doppler shifting of lines in its spectrum

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spectroscopic parallax

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The distance to a star derived by comparing its apparent brightness to a luminosity inferred from the star's spectrum

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spectrum binary

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A binary star whose binary nature is deduced from the presence of two sets of incongruous spectral lines

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stellar parallax

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The apparent displacement of a star due to Earth's motion around the Sun

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supergiant

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A very large, extremely luminous star of luminosity class I.

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tangential velocity

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That portion of an object's velocity perpendicular to the line of sight

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UBV photometry

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A system for determining the surface temperature of a star by measuring the star's brightness in the ultraviolet (U), blue (B), and visible (V) spectral regions

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visual binary

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A binary star in which the two components can be resolved through a telescope

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white dwarf

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A low-mass star that has exhausted all its thermonuclear fuel and contracted to a size roughly equal to the size of Earth

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accretion

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The gradual accumulation of matter in one location, typically due to the action of gravity

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Barnard object

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One of a class of dark nebulae discovered by E. E. Barnard

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bipolar outflow

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Oppositely directed jets of gas expelled from a young star

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Bok globule

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A small, roundish, dark nebula

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circumstellar accretion disk

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An accretion disk that surrounds a protostar

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cluster (of stars)

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A group of stars that formed together and that have remained together because of their mutual gravitational attraction

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cocoon nebula

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The nebulosity surrounding a protostar

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dark nebula

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A cloud of interstellar gas and dust that obscures the light of more distant stars

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dust grain

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A microscopic bit of solid matter found in interplanetary or interstellar space

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emission nebula

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A glowing gaseous nebula whose spectrum has bright emission lines

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evolutionary track

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The path on an H-R diagram followed by a star as it evolves

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fluorescence

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A process in which high-energy ultraviolet photons are absorbed and the absorbed energy is radiated as lower-energy photons of visible light

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giant molecular cloud

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A large cloud of interstellar gas and dust in which temperatures are low enough and densities high enough for atoms to form into molecules

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H II region

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A region of ionized hydrogen in interstellar space

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Herbig-Haro object

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A small, luminous nebula associated with the end point of a jet emanating from a young star

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interstellar extinction

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The dimming of starlight as it passes through the interstellar medium

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interstellar medium

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Gas and dust in interstellar space

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interstellar reddening

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The reddening of starlight passing through the interstellar medium as a result of blue light being scattered more than red

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nebula

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A cloud of interstellar gas and dust

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OB association

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A grouping of hot, young, massive stars, predominantly of spectral types O and B

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open cluster

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A loose association of young stars in the disk of our Galaxy; a galactic cluster

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protoplanetary disk

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A disk of material encircling a protostar or a newborn star

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protostar

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A star in its earliest stages of formation

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recombination

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The process in which an electron combines with a positively charged ion

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reflection nebula

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A comparatively dense cloud of dust in interstellar space that is illuminated by a star

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stationary absorption lines

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An absorption line in the spectrum of a binary star that does not show the same Doppler shift as other lines, indicating that it originates in the interstellar medium

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stellar association

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A loose grouping of young stars

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stellar evolution

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The changes in size, luminosity, temperature, and so forth that occur as a star ages

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supernova remnant

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The gases elected by a supernova

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supersonic

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Faster than the speed of sound

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T Tauri star

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Young variable stars associated with interstellar matter that show erratic changes in luminosity

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alpha particle

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The nucleus of a helium atom, consisting of two protons and two neutrons

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Cepheid variable

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A type of yellow, supergiant, pulsating star

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close binary

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A binary star system in which the stars are separated by a distance roughly comparable to their diameters

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color-magnitude diagram

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A plot of the apparent magnitudes (that is, apparent brightnesses) of stars in a cluster versus their color indices (a measure of their surface temperatures)

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contact binary

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A binary star system in which both members fill their Roche lobes

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core helium fusion

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The thermonuclear fusion of helium at the center of a star

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core hydrogen fusion

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The thermonuclear fusion of hydrogen at the center of a star

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degeneracy

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The phenomenon, due to quantum mechanical effects, whereby the pressure exerted by a gas does not depend on its temperature

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degenerate-electron pressure

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The pressure exerted by degenerate electrons

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detached binary

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A binary star system in which neither star fills its Roche lobe

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globular cluster

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A large spherical cluster of stars, typically found in the outlying regions of a galaxy

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helium flash

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The nearly explosive beginning of helium fusion in the dense core of a red giant star

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helium fusion

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The thermonuclear fusion of helium to form carbon and oxygen

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horizontal-branch star

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A low-mass, post-helium-flash star on the horizontal branch

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ideal gas

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A gas in which the pressure is directly proportional to both the density and the temperature of the gas; an idealization of a real gas

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inner Lagrangian point

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The point between the two stars constituting a binary system where their Roche lobes touch; the point across which mass transfer can occur

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instability strip

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A region of the H-R diagram occupied by pulsating stars

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long-period variable

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A variable star with a period longer than about 100 days

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main-sequence lifetime

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The total time that a star spends fusing hydrogen in its core, and hence the total time that it will spend as a main-sequence star

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mass loss

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A process by which a star gently loses matter

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mass transfer

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The flow of gases from one star in a binary system to the other

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metal-poor star

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A star that, compared to the Sun, is deficient in elements heavier than helium; also called a Population II star

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metal-rich star

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A star whose abundance of heavy elements is roughly comparable to that of the Sun; also called a Population I star

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open cluster

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A loose association of young stars in the disk of our Galaxy; a galactic cluster

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overcontact binary

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A close binary system in which the two stars share a common atmosphere

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Pauli exclusion principle

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A principle of quantum mechanics stating that no two electrons can have the same position and momentum

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period-luminosity relation

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A relationship between the period and average density of a pulsating star

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Population I star

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A star whose spectrum exhibits spectral lines of many elements heavier than helium; a metal-rich star

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Population II star

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A star whose spectrum exhibits comparatively few spectral lines of elements heavier than helium; a metal-poor star

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pulsating variable star

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A star that pulsates in size and luminosity

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red dwarf

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A main-sequence star with a mass between about 0.08 solar mass and 0.4 solar mass which has a fully convective interior and which never goes through a red giant stage

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red giant

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A large, cool star of high luminosity

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Roche lobe

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A teardrop-shaped volume surrounding a star in a binary inside which gases are gravitationally bound to that star

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RR Lyrae variable

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A type of pulsating star with a period of less than one day

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semidetached binary

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A binary star system in which one star fills its Roche lobe

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shell hydrogen fusion

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The thermonuclear fusion of hydrogen in a shell surrounding a star's core

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triple alpha process

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A sequence of two thermonuclear reactions in which three helium nuclei combine to form one carbon nucleus

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turnoff point

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The point on an H-R diagram where the stars in a cluster are leaving the main sequence

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zero-age main sequence

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The main sequence of young stars that have just begun to burn hydrogen at their cores

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zero-age main-sequence star

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A newly formed star that has just arrived on the main sequence

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antiparticle

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A particle with the same mass as an ordinary particle but with other properties, such as electric charge, reversed

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black hole

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An object whose gravity is so strong that the escape speed exceeds the speed of light

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black hole evaporation

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The process by which black holes emit particles

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collapsar

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A proposed type of supernova in which a black hole forms at the center of a dying star before the outer layers of the star have time to collapse

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equivalence principle

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In the general theory of relativity, the principle that in a small volume of space, the downward pull of gravity can be accurately and completely duplicated by an upward acceleration of the observer

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ergoregion

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The region of space immediately outside the event horizon of a rotating black hole where it is impossible to remain at rest

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event horizon

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The location around a black hole where the escape speed equals the speed of light; the surface of a black hole

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gamma-ray burst

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Objects found in all parts of the sky that emit a one-time intense burst of high-energy radiation

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general theory of relativity

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A description of gravity formulated by Albert Einstein. It states that gravity affects the geometry of space and the flow of time

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gravitational radiation (gravitational waves)

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Oscillations of space produced by changes in the distribution of matter

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gravitational redshift

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The increase in the wavelength of a photon as it climbs upward in a gravitational field

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Hawking radiation

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Light and particles made of matter and antimatter that emanate away from a region just outside a black hole's event horizon. The radiation occurs when one member of a virtual particle pair is captured by the black hole; the other member of the pair becomes a real particle and carries away some of the black hole's energy (and therefore, some of its mass). This loss of energy leads to black hole evaporation

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Heisenberg uncertainty principle

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A principle of quantum mechanics that places limits on the precision of simultaneous measurements

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intermediate-mass (mid-mass) black hole

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A black hole with a mass of hundreds of Suns

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length contraction

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In the special theory of relativity, the shrinking of an object's length along its direction of motion

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Lorentz transformations

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Equations that relate the measurements of different observers who are moving relative to each other at high speeds

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no-hair theorem

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A statement of the simplicity of black holes

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primordial black hole

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A type of black hole that may have formed in the very early universe

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proper length (proper distance)

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A length measured by a ruler at rest with respect to an observer

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proper time

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A time interval measured with a clock at rest with respect to an observer

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Schwarzschild radius

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The distance from the singularity to the event horizon in a nonrotating black hole

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singularity

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A place of infinite space-time curvature; the center of a black hole........ Equations describing the matter within the event horizon indicate that the object's entire mass is crushed nearly to a single point... That single point is the SINGULARITY (which is at the center of the Black Hole)

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spacetime

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A four-dimensional combination of time and the three dimensions of space

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special theory of relativity

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A description of mechanics and electromagnetic theory formulated by Albert Einstein, which explains that measurements of distance, time, and mass are affected by the observer's motion

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stellar-mass black hole

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A black hole with a mass comparable to that of a star

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supermassive black hole

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A black hole with a mass of a million or more Suns

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time dilation

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The slowing of time due to relativistic motion

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virtual pair

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A particle and antiparticle that exist for such a brief interval that they cannot be observed

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Gravitational Redshifts

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caused by time flowing at different rates at different locations No motion is involved

ASTRO Midterm Exam #2: VOCAB (ch. 16-21) – Flashcards

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