Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
33 Cards in this Set
- Front
- Back
|
fundamental properties of stars
|
distance
luminosity (intrinsic brightness) (total power) temperature |
|
|
nearest star
|
proxima centauri
3 star system |
|
|
100 billion stars
|
milky way galaxy
90% Hydrogen (atomic & molecular) 9% Helium 1% everything else (Carbon, Oxygen, Iron, dust ….) |
|
|
100 billion gallexies
|
universe
10^22 stars |
|
|
trigonometric parallax
|
objects closer to us appear to move more.....(d=1/p)
....distance (in parsecs)=1/parallax (arcsecs) most accurate for distance |
|
|
parsec
|
the distance at )which 1-arcsec subtends 1 A.U.....
1 pc = 3.26 Light-years =3x10^16m Typical separation between stars in galaxies is 1 parsec. |
|
|
ways stars move
|
In addition to Parallax
(Apparent motion) transverse component (proper motion) and line of sight component (dopler) |
|
|
hipparchos (satellites)
|
yielded accurate distances to over
120,000 stars. |
|
|
inverse square law
|
d1=1
d2=4 d3=9 Increasing a star’s distance by 3 means our eye receives 1/9th as much light. |
|
|
luminosity function
|
stars like sun, relatively common
high curve, low luminosity common low curve, high luminosity rare |
|
|
black body
|
stars emit light like a black body; temperature gives off color
|
|
|
photometry
|
measures relative brightness by a series of filters....
Cool star emits more green photons; Hot star emits more UV and violet photons. |
|
|
color lies
|
If there is a lot of dust between the star and us, the star will appear redder in color than it
actually is. |
|
|
spectral classification of stars
|
obafgkm (+like that 4 brown dwarfs)
hot 2 cool, type and # of absorption lines change |
|
|
balmer absorption line
|
electron absorbs a photon of the correct quantized energy and jumps from the n=2 level to a higher level
|
|
|
brown dwarfs
|
failed stars;
to small; glow because of kevin-hemholtz contraction; peak wavelength in infared |
|
|
determining the radii of stars1
|
measure stellar diameter
not very effective |
|
|
radii of stars 2
|
interferometers 2 combine light from tons of telescopes to make higher res,
|
|
|
radii of stars 3
|
ellipse by moon
5% of stars |
|
|
radii of stars 4
|
stephen's law:
(Energy Flux=F = (o w tail)*T^4 Luminosity of a Star (L): L =4pi R^2 x(o w tail)*T^4 |
|
|
stellar radii
|
factor of 60,000
sun is med-low giants, super, dwarfs |
|
|
Hertzsprung-russell diagram
|
luminosity l
l ________ surface temp. * main sequence stars |
|
|
luminosity class
|
The width of spectral lines
can be used to define luminosity classes * mass and age |
|
|
spectroscopic parallax
|
find distance;
find mag and class; use spectral line 2 find lum. use inverse square * can see several thousand parsecs |
|
|
stellar masses
|
binary pairs;
visual binaries; spectroscopic binaries; eclipsing |
|
|
visual binaries
|
keplers 3 law
most accurate for finding masses |
|
|
radius
|
depends on mass
|
|
|
star life age
|
Stars more massive than the Sun live much shorter lives.
Stars less than the Sun live much longer lives. |
|
|
reflection nebulae
|
The bluish haze is
evidence of dust in the cloud....Starlight is scattered and reflected by these small grains... The grain size ~500 nm...i.e equal to wavelength of visible light... Scatter blue more efficiently than red |
|
|
dark clouds
|
very cold
T = 10 - 100 K Temperature low enough for hydrogen to form molecules 10^4 -10^9 particles/cm3 (atoms, molecules & dust) Compared to <HII> gas ~ 10 3 atom/cm3 ; density air in this room ~10^19 atoms/cm3) |
|
|
dust clouds
|
makes stars appear redder
NOT a Doppler shift |
|
|
dust is a catalyst
|
1. molecules form on surface
2. shield 3. coolant |
|
|
star formation
|
Star formation happens when part of a dust
cloud begins to contract under its own gravitational force; as it collapses, the center becomes hotter and hotter until nuclear fusion begins in the core. |
