Intro To Astronomy Flashcards
Central meridian (zero point for measuring positions in sky)
Vernal equinox
Right ascension (RA)
Longitude (expressed as hour angle)
Declination (δ)
Latitude (expressed as an angle)
Synodic day
Solar day, time for earth to make one full rotation around the sun (24:00)
Sidereal day
Time for earth to be at the same point relative to the sun from the point of view of an earth observer (23:56:04)
Length of year (SI days)
365.2422 SI days
1 AU
Distance from Earth to the Sun (1.5 x10^11m)
Parsec
Distance corresponding to a parallax angle of 1” (3.086 x10^16m)
Parallax
Apparent motion of stars due to the Earth’s orbit around the Sun, movement by an angle 1AU/d(pc)
Proper motion
The transverse component of a star’s drift (i.e. motion in space)
Flux
Received light power per unit area (W/m^2)
Apparent brightness
Received light power (W)
Luminosity
Total energy-rate (power) emitted (W)
Absolute magnitude
The apparent magnitude we would observe if the object was 10pc away
Visible window of wavelengths and frequencies
λ = 400-700nm, f = 4-8 10^14 Hz
Black body emission
- Looks like a poisson curve
- T increases ⇒ BBR increases at all wavelengths
- T increases ⇒ peak at shorter wavelength
Planet
A celestial body that
a) is in orbit around the Sun,
b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and
c) has cleared the neighbourhood around its orbit
Dwarf planet
A celestial body that
a) is in orbit around the Sun,
b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,
c) has not cleared the neighbourhood around its orbit,
d) is not a satellite
μ
Mean mass per particle
Open cluster
Groups of a few 100-1000 stars, <10 pc across
These clusters a wide range of ages
Globular clusters
10^5-10^6 stars in a spherical cluster, 20-50 pc across
All very old, ~10^10 years
Mass-luminosity relation
L ∝ M⁴
Importance of clusters for stellar evolution
- same distance from earth
- have formed from a gas with the same composition
- same age
Chansrakhar limit
Maximum mass of a white dwarf due to relativistic limit
M_Ch = 1.33M☉
Cepheid variable stars
Giants that show regular pulsations, whose pulsation period only depends on the absolute magnitude of the star.
Hence measuring this period and apparent magnitude gives distance
Doppler shift of galaxy light
λ’ = λ₀(1+v/c)
Where λ’ is observed, λ₀ is rest wavelength
Redshift z
z = (λ’ - λ₀)/λ₀ = v/c
Cosmic Microwave Background
Peaks at λ ~ 1mm and T = 2.7K
Kepler’s Third Law
When m<
Hydrostatic equilibrium
dP/dR = -Gρ(r)M(r)/r²
Evolution of stars according to mass
0.8 M☉ ≤ M ≤ 8M☉ progresses to white dwarf
8 M☉ ≤ M ≤ 30-40M☉ progresses to neutron star
M > 30-40M☉ progresses to black hole
Cooling of white dwarf
t_cool = (GM²)/RL,
mass of WD ~ 0.6 M☉
Age of universe
1/H₀*Mpc/km
Luminosity in terms of radius of object and temperature
L = 4πR²σT⁴
Diffraction proportionality
Δα ∝ λ/D
Hubble’s law
v(km/s) = H₀*d(MPc)
Temperature of earth
~290K
Radiation pressure due to sun at distance d
P_rad = L☉/4πcd²
3 zones in solar system
Inner zone: gases escape by radiation pressure, compact terrestrial planets
Middle zone: lots of ice, gas giants and icy giants
Outer zone: methane ice, no collisions bc low density, so Kuiper belt with small objects
Core temp, mass and radius relation
T_c ∝ M/R
Lifetime of a star
t = E/L, E energy
H-R diagram
X axis temperature (decreasing)
Y axis luminosity (increasing)
