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34 Cards in this Set
- Front
- Back
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How many stars are there in a globular cluster
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- 10^5-10^6 stars
- In the HALO mostly though a few in the Disk and Bulge - Few heavy elements (Population II) - OLDER >10^10 years |
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How many stars are there in a open cluster
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- 10^2 – 10^3 stars
- Only in DISK of the galaxy - Heavy elements in the Stars (Population I Stars) – heavier than helium - Younger < 109 years |
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What is special about globular clusters
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When you map them on an H-R diagram - there is a common turn off on the main sequence - thus they are all the same age
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Diameter of the Milky way galaxy
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100,000 light-years - DISK
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distance to the center of the galaxy
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25,000- 30,000 ly from Solar System to middle of MWay
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the thickness of MWay galaxy
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5000ly at Bulge
1000ly at disk |
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Nearest Spiral Galaxy
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2,000,000 light years
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Nearest star
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4 ly
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Time it takes light to reach us from the sun
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8 minutes
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Age of the Universe
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13.7 times 10 ^9 years
(billion) |
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Mass of the MILKY WAY (not the Universe)
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M = 10 times the M of Sun
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DESCRIPTION – Five fundamental properties of light as an EM wave.
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a.) Speed of propagation = c
b.) Direction of propagation = sometimes the direction is not toward earth … we detected it FROM here c.) Wavelength – lambda (λ) Frequency is the same – because of the speed of propagation – same (distance from peak to peak) d.) Polarization – electric go one way – the magnetic the other – The plane in which the ELECTRIC field oscillates – linear or perpendicular (some lenses are polarized) e.) Intensity/amplitude – how HIGH the peaks are |
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The range of visible light
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0.4-0.7 microns (10 ^-6 m)
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Other key properties of light
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KEY PROPERTY of LIGHT
1.) REFRACTION – light is BENT when it goes from one medium to the other – Prism - all wavelengths refracted at diff. wavelengths 2.) DISPERSION – is differential refraction – the result is a rainbow - |
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Importance of Spectral Lines in Science
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1.) Which elements are present –
2.) Relative abundance of different elements and molecules – 3.) Physical conditions in the thing that is producing the light - Temperature and density of elements – 4.) VELOCITY - The motion of the elements – Doppler shift |
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Why don’t electrons crash into the nucleus???
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It is because the energy levels are quantized and they cannot BE ZERO – the probability of the electron going into the nucleus is almost zero … etc.
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What is hydrostatic equilibrium?
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-fluid not moving in balance - Everywhere in the star – there are no NET forces – or the forces are balanced –
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Temperature measures what?
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The speed of the particles
½ mv2 = 3/2 (kT) where m= mass v= velocity k = Constant |
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DENSITY of WATER
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1 gm cm-3
Same as humans |
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Photosphere – density
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10^-7 !!!! 10,000 times LESS dense than water
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What is the state of matter in the center of the sun?
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Plasma is in the center of the sun – atoms stripped of electrons – heat and collisions buts apart atoms and make electrons…
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What is the importance of the
STRONG nuclear force |
holds protons and neutrons together in the nucleus …
- in STRONG PRESSURE - THE NUCLEI get close enough to one another that the attractive short-range nuclear strong force can overcome the repulsive electric force… |
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Most important source of E from sun
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GAMMA RAYS - though they are trapped in the core and do not escape they power extra reactions in the core
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How much mass is converted to E in the proton-proton chain?
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MASS of 0.003 mass of a proton converted to ENERGY
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WHy can't stars fuse beyond iron?
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Because Iron is the most strongly bound nucleus and it TAKES energy to fuse iron - there is no mass converted into E in the reaction.
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What important matter is released in a Supernova explosions?
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1.) Elements made during evolution
2.) Elements made during explotion… |
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Why does collapse of massive star lead to supernova explosion?
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- At some point, the core becomes very stiff and the stuff falling on to it from the outer parts of the star – bounces back
- 2 different mass layers of matter rushing toward stiff core |
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How do we know how far away the sun is?
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We use the moons of Jupiter as an orbital clock -
THen we can get AU - so that we can use it in parallax angles later... |
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STELLAR PARALLAX:
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- It is the apparent motion of nearby stars against a more distant background…or stars or galaxies or quasars…
- CAUSED by the earth’s orbital motion around the sun |
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parallax angle
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which is HALF the measured shift in a star’s positions over a 6month interval
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Brightness formula
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b= L/4 (π)d2
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STANDARD CANDLE
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– anything that has the same luminosity as all the other members of its class
- FIGURE OUT how far it is by measuring brightness and using it to get the distance… |
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Cepheid Variable Stars
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Class of evolved or POST main sequence star (red giant land somewhere) which PULSATES
- AND whose luminosity varies in a regular way … If you plot the PEAK luminosity vs period in days Period TELLS us the LUMINOSITY – then use the Inverse Square law to get the distance…. |
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How to get d for Cepheids:
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1.) Measure period
2.) Infer L from known period L relation… (how is it known – nevermind for now) 3.) Measure brightness with a telescope – 4.) D with inverse sqare law… |
