Flashcards in Stars and Star Terminology Deck (30):
What is the absolute magnitude of a star?
It is the magnitude that a star would appear to have if it were at a distance of 10 pc from the Sun
What is the apparent magnitued of a star?
It is the brightness of an astronomical object, as observed on Earth and referred to the appearance of some objects chosen as standards. The scale of magnitudes is defined so that a difference of 5 magnitudes corresponds to a ratio of 100 in observed radiation intensity
What is a binary star?
A binary star is when two stars are in orbit around one another.
What is a black dwarf?
It is the final state of stellar evolution, when a star has used up all of its energy resources and can no longer radiate
What is a black hole?
Body that is so massive and so compact that no light can leave its surface. Suggested by General Theory of Relativity
What is a cepheid variable?
A cepheid variable is a type of star with regular variation in its brightness, named for Delta Cephei, the first star recognized of this type. These stars play an important role in the determination of the scale of distances to galaxies
What are circumpolar stars?
They are stars that are close enough to the celestial pole that they do not rise and set each night but can be seen to move around the pole in a circular path. Latitude of observer determines which stars appear circumpolar
What is a constellation?
A constellation is a group of stars that seemed to suggest the shape of some god, person, animal or object. Now a term used to designate a region of the sky, of which there are 88.
What is the Crab Nebula?
Remnant of the supernova observed in 1054 AD, now observable as an expanding and tangled cloud of gas, with a pulsar at the center
What is a dwarf star?
A dwarf star is a main-sequence star of low luminosity
What is an eclipsing binary star?
A binary star whose mutual orbit is viewed almost edge-on so that light observed is regularly decreased each time one star eclipses the other
What is an emission nebula?
A cloud of interstellar gas that glows because of ultraviolet radiation absorbed from a nearby hot star
What is a globular cluster?
It is a tight cluster of stars that is circular and symmetrical, as opposed to open or galactic clusters
What is luminosity?
The rate at which radiant energy is emitted by a star or other object, usually expressed in erg/sec
What is meantby luminosity class?
Classification of stars on the H-R diagram within the same spectral class
What does the main sequence refer to?
The band on the H-R diagram, populated by stars that derive their radiant energy from the fusion of hydrogen to helium in their cores
What is a neutron star?
A neutron star is composed of neutrons except for a very thin surface layer of atoms. Neutron stars have masses similar to the Sun but dimensions not much larger than the Earth, and , as a result, have very high densities
What is a nova?
Abbreviation from nova stella, Latin for new star, literally meaning the sudden appearance of a star where none had previously been known. Term now applied to sudden large brightening of a star, followed by a less rapid decrease in brightness
What are optical binary stars?
Pair of stars that appear to be related because they seem close together, but are actually situated at very different distances from the Earth
What is a planetary nebula?
Relatively thin shell of gas, blown off from and illuminated by a very hot star. Expands at high speed as it disperses into the interstellar medium
What are RR Lyrae variable stars?
Class of variable stars with periods less than 1 day
What is a red giant?
A red giant is a large star with relatively low temperature but high luminosity; a stage in stellar evolution after a star has left the main sequence
What does sidereal mean?
Related to the stars. Thus sidereal day, month, period, year: lengths of time intervals specified by motion of some object relative to the stars, as opposed to apparent lengths of those time intervals that will depend on the Earth?s own movements
What is the spectral class?
Classification of stars by the spectral features, into groups designated by O, B, A, F, G, K, M. This grouping also corresponds to surface temperatures
What is a spectroscopic binary star?
A type of binary star whose components are not seen separately, but whose spectrum shows periodic wavelength shifts that can be interpreted as the results of orbital motion
What is a red supergiant star?
It is the most luminous class of stars
What does variable star refer to?
A star whose luminosity changes. This designation will include stars with explosive changes ( novae and supernovae) as well as cyclic changes (Cepheids and RR Lyrae)
What is a visual binary star?
A visual binary is a star whose two components can be seen by telescope to be separate
What is a white dwarf star?
Star that is less massive than 1.4 times the solar mass, that has consumed almost all of its nuclear fuel and has contracted to a size not much larger than the Earth. Characterized by high surface temperature but small luminosity, as compared to the Sun. White dwarfs fall below the main sequence in the H-R diagram