astro

how to find particle denisty

number of particles / volume

density / mass of particle

how to find number of particles

mass of universe/mass of particle

what is the composition of the universe

90% H, 10%He, 0.01% everything else

how to find number of molecular gas

density / (2 x mass of hydrogen)

how to find number of atomic gas

density / mass of hydrogen

how to find number of ionized gas

( 2 x density) / mass of hydrogen

what is the force of gravity

weak, attractive, radial force

what is the total energy of an object

start energy + energy gained ( not linked to speed )

what is the work done due to energy

derived from integrating the gravitational force, as F is not constant with r

what is the escape velocity of an object

KE = gravitational

what is the orbital velocity of an object

gravitational = centripetal

what is kepler’s first law

planets orbit in ellipses with sun at one focus not the centre

how to find eccentricity of an orbit

sqrt ( 1 - (b/a)² )

what is kepler’s second law

planets sweep out equal areas in equal times, as there is a conservation of angular momentum (m v r sintheta)

what is kepler’s third law

period² = r³

what is a binary system

centre of mass is stationary and shared, objects are on opposite sides to conserve momentum and have the same period

how to find the parallax of an object

distance to object / distance to sun

what is parallax

change in position due to motion of earthw

what is proper motion

velocity (km/s) = proper motion (arsec/yr) x 4.74 x d (pc)

what is a parsec

if parallax = 1arsec and distance is 1pc

how many arsecs is 1 degree

3600

what is the equatorial system

declination - 0 at equator +_ 90 at north/ south

right ascension - in hours

how to find right ascemsion in arsec

RA(sec) x 15 x cos

what is the equation for flux

what is the equation for magnitude in terms of flux

what is equation of magnitude in terms of distance

what is a Cepheid variable

strict periodicity, longer peirod = higher luminsity

graph and peak for a supernova 1a

-19.3

what is the EM spectrum

gamma, xray, uv, visible, ir, micro, radio

what is radiation

object absorbs and emits photons of all wavelenghts with perfect efficiency

what is weins law

what is stefans law for flux

what is stefans law for power

what is the equation for luminosity

surface area x flux

what is the emitted energy over time

luminosity x time

what is the most perfect blackbody

CMBR

what a convex lens

converging

what is a concave lens

diverging

how to find power of a lens

1 / focal length

how to find distance of focal length

1/f = 1/distance from object and lens + 1/distance from lens and image

what are the images from a lens dependent on focal lenght

equation for magnification

objective/eyepiece

what is a refracting telescope

needs large objective focal lens, heavy - experiences chromatic aberration ( blurry/colourful images0

what is a reflecting telescope

mirrors, large, parabolic - spherical aberration ( not in focus)

what is the power of a lens

s = perpendicular distance between image and principle axid

what is the focal ratio

smaller value = brighter image, less detail, wide fov

what is the diffraction limit

what is atmospheric turbulence

pockets of air at different temps causing differential refraction

typical values for atmospheric turbulence

r0 - 5-30cm

t0- 1-100ms

what is an interferometry

combine line for N telescopes spread of distance d, with diameter D

what is the resolution of a telescope

what is snell’s law

which light bend more

blue bends more than red

what is the diffraction grating equation

why are CCDs better than light

larger quantum efficiency - 70-80%

large charge transfer efficiency

large dynamic range - can count high number of electrons

how to CCDs work

convert photons to measurable light, photo electric effect, use silicon crystals

what is the equation for v from the doppler shift

what is the equation for z

how to use doppler effect for exoplanet detection

wobble of star is large due to gravitational effect of planet

properties of low mass stars

cooler, smaller, fainter, higher density

properties of a stellar cluster

same age- found from main sequence turn off

luminosity of main sequence stasr

what is the equation for energy in a hydrigen nucleus

what is the equation for wavelength in any nucleus

x nucleus number²

what are the hydrogen line series

n=1 - Lyman UV

n=2 - Balmer optical

n=3 - Paschen infrared

equation for dynamic timescale

equation for hydrostatic equlibrium

negative pressure gradient

potential energy from constant density

total momentum

total velocity for constant velocities

total velcity for random velocities

equation for thermal energy

what does the virial theorem state

what is stellar nucleosynthesis

gravitational contraction- releases PE

nuclear fusion- produces right amount of energy needed

multiple reaction chains dependent on temp and density of star

what is the pp-cycle

energy release from fusion of 4 protons to 1 He nucleus as there is a mass deficit

energy needed in a star synthesis

luminosity / mass

why are planets stellar thermostats

can self-regulate temp, by increasing radius so lower temp and decrease in energy production

how long can a star shine

efficiency factor x mass / luminosity

proportion of luminosity and mass in main sequence star

proportion of time and mass in a main sequence star

max nucleon binding energy

56Fe, fusion for lighter, fission for heavier

radius for a black hole

escape velocity = c

galaxy calssification system

hubble’s tuning fork

E- ellipitcal, S- spiral, SB- spiral bar, irregular

10^7 - 10^13 Molar masses

properties of spiral galaxies

central bulge or bar, rotating disk, spiral arms(stars form(, stellar halo (globular clusters), younger stars orbit centre, random velocities, 10^9 - 10^12 molar masses, mostyl dmoinated by dark matter

properties of elliptical galaxies

little structure, old stars, little gas/dust, no star formation, product of merger of glaxies, E0 -circular - E7 -flat

properties of irregular galaxies

no clear structure, gas rich and star forming, undergoing merges, small

properties of supermassive black holes

centre of massive galaxies, not stellar remnants, active accretion disk which fuels star formation, cannot be views, 10^6 - 10^10 solar masses

how does gas work in a galaxy

makes up 5-25^ of mass and extends out of disk, is observed through 21cm emission from H gas,

how is H gas viewed

spin of electrons and protons gives 2 energy states, transition between states rises 21cm emission line, experiences doppler shift which shows rotation

how to find M(R) and velocity of a planet

centripetal = gravitational

where masses are m and M(R)

why does velocity profile prove dark matter

mass increases linearly from centre of galaxy, must be in spherical halo that extends further than stars and gas

properties of dark matter

cannot interact electromagnetically only gravity, emits no light, not baryonic

properties of the universe

homogeneous(same at any location), isotropic(same in all directions), gallilean invariance (same laws of physics)

what is the hubble flow

H = 70, v = km s^-1 , D = Mpc

what is the hubble time and radius

expansion started at the same time for all galaxies, t = 1/H, radiues = H time x c

what is the distance ladder

parallax, cepheid, supernova 1a

what is look back time

galaxies are seen in the past, z=1, time = 8Gyr

what is the evidence for the age of the universe

radioactive decay of elements, must be older than earth

evidence of age of stars

radioactive decay, ratios of decay give age, oldest stars in milky way are in globular clusters

when is peak star formation for galaxies

z=2 (10Gyr), declined by factor of 10 now