Karteikarten
Stars and cosmology: HR diagram, magnitudes, parallax
Karten in diesem Stapel (57)
- 1Black Body LawsRadiators surface temperature determines the characteristics of its spectrum
1.shape of spectral curve
2. location of the peak of energy output
3. total area under spectral curve - 2Planck's LawBlack Body spectral Curve has a single peak or color which is brightest
- 3Wiens Lawwavelength of the peak is inversely proportional to the temperature of the object emitting the black body radiation. for example if the temperature of the object increases, then the wavelength of its spectral peak decreases.
- 4Smaller wavelengths are... (referring to spectral curves)Blue. Temperature of object decreases
- 5Larger wavelengths are... (referring to spectral curves)Red. Temperature of object increases
- 6The Law of Stefan and BoltzmannLuminosity of black body radiator increases with increasing surface temperature, and also increasing with surface area.
- 7Mathematical representation of Wiens Lawsurface temperature=Wiens constant/wavelength of peak
or
(surface temp1)=(wavelength of peak1)^-1
(surface temp2=(wavelength of peak2) - 8Mathematical representation of Stefan and Boltzmanlumiosity1=(surface area1) (surface tem1)^4
luminosity2=(surface area 2)(surface temp2) - 9HR DiagramHR diagram is used to show each stage of a star on one diagram
white dwarfs-main sequence- evolved giants - 10HR DiagramY-axis: Total Brightness
X-axis: Surface Temperature - 11Atomic composition of a star and temperature range96 hydrogen atoms and 4 would be helium.
Temperature range: 3,000 to 30,000 kelvin - 12Russell-Vogtentire life cycle of star is determined by mass and composition but all stars basically composed of the same thing so really depends on mass.
- 13Spectrum colorsRed-->violet
goes up increasing in photon energy - 14stars can have different spectra because...spectra is based off of composition, temperature, pressure, state, size, luminosity, distance and motion
- 15Physical process main sequenceHydrogen fusion- hydrogen turning into helium
- 16physical process red giant stageHelium is collecting in core, hydrogen fusion moves out creating a shell around the core.
- 17physical process horizontal giant stageHelium fusion begins at 100 million Kelvin
3He-->C+energy - 18physical asymptotic giant stagecarbon collects in the core, helium fusion moves to a shell
- 19celestial sphereimaginary orb around us and what we see
- 20horizontal coordinatesAzimuth- the angle from the north cardinal point eastward
Altitude- then angle above or below the horizon
Zenith- maximum altitude 90 degrees directly above observer
Nadir- minimum altitude of -90 degrees directly below observer - 21Prime Merdianis the zero for right ascension, connects the celestial poles with the March equinox
- 22Celestial longituderight ascension- it increases eastward on celestial sphere
- 23Celestial latitudedeclination increases northward and decreases southward
- 24What generation is the sunThe sun is third generation star because of the measured quantities of heavier elements
- 25Planetary Nebula Ejectionlow mass stars
atmosphere expands then disperses - 26Supernova ExplosionHigh mass stars
core collects iron-core collapses
high temp and high densities - 27Geometric Parallaxonly direct method for determining distances to stars makes use of triangles
- 28Parallaxdefined as the apparent motion of an object due to the motion of the observer
ex: driving in a car and watching objects outside the window move past you, nearby objects appear to move more quickly than distant objects - 29Parallax in astronomythe moving object is earth-foreground stars will appear to change their relative locations when compared with background objects- the ultimate background object is the celestial sphere
- 30Annual shift angleMaximum baseline is when earth is located at opposite sides of its orbit which occurs every six months. We measure the apparent angle to the star and call it the annual shift
- 31Parallax angleHalf of the annual shift angle
- 32parallax-distance relation:d=1/p
d=distance in parsecs
p=angle in arc-seconds
1=constant proportion that arises as a result of our choice of units - 33Larger magnitude stars are...fainter
- 34Apparent magnitude (m)how bright the star appears from the earth bound observer- in relation to star's flux
- 35Absolute magnitude (M)how bright the star would appear if it were at a distance of 10 parsec. absolute magnitude is related to stars luminority
- 36Flux equationLuminosity divided by 4pie times distance squared
- 37Using magnitudes the flux equation becomes the distance modulus formulam-M=5 log(d)-5
- 38Johnson-Morgan filter system-UBVRI filter
U-ultrviolet (almost)
B- visible, blue
V-visible, yellow
R-visible, red
I-infrared (almost) - 39color indexFlux is measured in magnitudes m. Flux through a filter gets the subscript of the filter. So if it comes through the v filter it becomes mv or just V.
-the distance modulus would be V-Mv=5 log (d)-5 - 40color indices are always reported as...bluer magnitude minus redder magnitude so B-V but NEVER V-B
- 41Color standard for stars is...Vega.
stars are either redder than Vega or bluer than Vega.
Its color indices are all defined as 0 - 42Galaxyan island of stars, gas, and dust, all held together be gravity and surrounded by empty space
- 43Diameter of Milky Way100,000 light years across
- 44our galaxy is a disk shaped galaxy meaning...The brightest stars are located in a flat round region. . In addition to the disk, the stars near
the center of the Milky Way are arranged in a roughly spherical shape called the spheroid or bulge. Surrounding
the disk and bulge is a collection of very faint, low mass stars in a region called the halo. Halo stars are generally
too faint to be seen, even in photographs. - 45star formation occurs...in the mid-disk
- 46Globular clustera spherical collection of stars that orbits a galactic core as a satellite
-tightly bound by gravity
-younger than stars in open cluster - 47Open Clusteralso known as galactic cluster, is a cluster of up to a few thousand stars, that were formed from the same giant molecular cloud and have roughly the same age.
-older the stars in globular cluster - 48spectroscopic parallaxrevised method of flux equation for finding distance to the stars
1. measure directly the star’s apparent magnitude,
2. obtain spectroscopic or photometric information to find the star’s absolute magnitude,
3. compute the distance modulus,
4. solve for distance. - 49Stars exhibit a...line absorption spectrum
- 50By Kirchoffs 3rd law all stars have...By Kirchoff’s 3rd law, all stars have a high temperature and high density
gaseous core, surrounded by a lower density and lower temperature gaseous atmosphere - 51Local groupOur Milky Way is located in a galaxy group called the Local Group. The Local Group is a part of the Local
Cluster, itself part of the Local Supercluster of galaxies - 52CosmologyCosmology is the study of the universe as a single object
- 53multi-component universeOur
universe is a multi-component universe, meaning that there is more
than one type of energy in our universe.
we have decelerated and accelerated - 54the fact of expansion means...universe will be less dense in the future
- 55Hubble time13.7 billion years ago
- 56called Hubble's parameter because...its not actually constant
- 57Dark energyis intensifying but we don't know what it is
-like to see it be non-photon operational
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