DIS 01

Astronomical Distance:
1 AU(Astronomical Unit, the distance between sun and earth) = 1.5 x 10^8 km = 9.16 x 10^7 miles -> measure solor system
Lightyear(光年, which is a distance unit) = dist. light travels in 1 year = 9.45 x 10^12 km -> measure dist. between stars
parsec = 3.26 lightyears = 3.086 x 10^13 km -> measure galaxies+bigger
C = 3 x 10^5 km/s
c = lambda (wavelength) * v(frequency hz = 1/s)
E = hv = hc / lambda

DIS 04

  1. The sun is 1 AU
  2. M = 2 * 10 ^30 kg = 1 MO solar mass = 330,000 Earths
  3. Wien’s Law: ASTRON 103 - 图1

image.png
Layers of the sun:

  1. Core
    1. where the nuclear fusion (H -> He: 3.9 x 10^25 W per sec)
    2. very dense, T = 1.5 x 10^7 K
  2. Photosphere
    1. what we see -> emits light
    2. T = 5800 K
    3. lowenouth dens.
  3. Chromosphere
    1. low dens, T = 50,000 K
  4. Corona
    1. lowest des., T = 10^6 K
    2. see only during solar eciipses

Sunspots

  1. cooler regions on the photosphere caused by the magnetic field of the sun
  2. T = 4500 K
  3. can be larger than the size of the Earth
  4. As magnetic field gets twisted, it eventually breaks and release a ton of energy
  5. Solar cycle: every 11 years, number of sunspots peak at a maximum , then clearance again

DIS 05

Parallax, Luminosity and Brightness

  1. Distances to stars are found using parallax
  2. Apparent motion of an object due to changing viewpoint
  3. dpc = 1 / Parcsec
  4. 1 pc = 3.26 lyrs = 3.09 x 10^13 km
  5. 1 arcsecond = 1/3600 degree
  6. Farther away star(d increase), the smaller the angle(p decrease)

Luminosity

  1. how much energy a star emits per second, not dist. dependent

Brightness

  1. measure of how much of that energy reaches us, dist. dependent
  2. B = L / 4Pid^2

Magnitude

  1. Absolute Magnitude = equivalent to luminosity, not dist. dependent
  2. Apparent Magnitude = equiv. to brightness, dist. dependent

DIS 06

SUMMARY UNIT

  1. Milk way = 100,000 lyrs
  2. light, c = lambda _ v, E = h _v = h C / lambda -> long lambda, low energy

long-lambda
radio, Microwave, IF
visible
Roy G BIV ( 400 - 700 nm)
UV, X-ray, Gamma
Short-lambda

  1. Black body: lambda max = 2.9 * 10^ 6 / T, lambda decrease, T increase.
  2. v is + if away, - if towards
  3. watt = joule / sec

DIS 07

Kepler’s Laws + Stellar Classification

  1. perihelion：近日点; aphelion：远日点, planets orbit faster when closer to their star
  2. M1 + M2 = a^3 / p^2

M1 + M2 = total mass of star + planet(in Mo), a = semi-major axis(in AU), p = time for one orbit (in yrs.), for S.S., a^3 = p^2

  1. Classify star with surface temperature:
    1. Wien’s Law -> T = 2.9x10^6 / lambda_peak
    2. Luminosity -> L = 4 Pi R^2 x mu*T^4
  2. Spectral Types: O B A F G K M
  3. Main Sequence: where they will spend majority of life, NO moves on MS.

DIS 08

  1. Molecular Cloud - cloud begins to clump from star or supernova
  2. Gravity starts acting more strongly, pulls coumps together and collapses to protostar
    • M < 0.08 Mo, never evolves past this. No fusion stars
  3. Gravity contracts gas so much, heats up, that when the core ~12 millon K, fusion of H -> He starts and the star stops collapsing, => Main Sequence Star, sun = 10 billion yrs,
    • spends entire MS fusing, H -> He in core
    • stars relatively stay the same
    • cooler/low-mass stars use up their hydrogen more slowly than hotter / high-mass stars.
  4. Eventually, no H hot enough to fuse He, so fusion stops!
  5. Gravity wins, core contracts/ heats up
  6. Outer shell get pushed by heat from the core, core contracts, outer layers expand and cool -> Red Giant for low-mass stars; Blue supergiant for high-mass stars
  7. Core contracts -> new hydrogen now falls into the core and can now be used, Helium core heats up enough for He fusion.
  8. He can fuse into 4 Be, but that isn’t stable, so instead most fuse 3He -> 6C
    1. Helium ignites -> helium flash star contracts slightly yellow giant (super) for high mass stars