Components of the universe Flashcards
Astronomical unit
Distance from earth to sun, approx 150 million km
Light year (ly)
Distance light travels in a year. Also light hours, minutes etc. 1AU approx 8 light minutes. Light second approx 300 million metres (speed of light)
Speed of light
3.00 x 10^8 ms^-1 So 300 million metres per sec
Angular size and angular resolution
Size angle between 2 imaginary lines, drawn from observer to what they are observing. Angular resolution, smallest angular size that can be determined with an instrument. Eye angular res 0.01 degrees. If angle between 2 stars smaller than angular res then appears as one object
Angular size, actual size and distance
angular size (degrees) = 57 x (actual size/ distance observer to object)
Gravitational wave detection
Vibrating space, information encoded in vibrations
Semimajor axis
Largest distance from centre of ellipse to orbit
Eccentricity of an object’s orbit
Decree of elongation of orbit (in other words how elliptical). e=0 (circular obit) - close to 1
Kepler’s laws
1st:) relates to elliptical orbits. 2 focii on any orbit. Sum of distances from any points on elipse to the 2 focii is the same 2nd:) Speed - objects in circular orbits move at constant speed, in elliptical orbits objects move faster when closer to central body. 3rd:) Orbital period (p)^2 = (ka^3/M+m).M mass of central body, m mass of object orbiting, k constant, a length of semimajor axis. For our solar system, can user p^2=[1 year^2 au^-3] a^3 (au is astronomical unit)
Kepler’s third law
The square of the orbital period of a planet is proportional to the cube of the semimajor axis of its orbit
Gradients of the graphs with a^3 against p^2 for 2 different systems also gives ration of mass of central body.
Eg done with the sun and jupiter (with planets and jupiter’s galilean moons) grad of sun graph, grad of jupiter graph gives ration of masses of sun and jupiter
Extrasolar planet (exoplanet)
Planet orbiting stars other than the sun (eg proxima b orbiting proxima centauri, our nearest star outside our solar system)
Goldilocks zone (planets)
Far enough from star to be not too hot, close enough to be not too cold…so life more likely
Transit technique and Radial velocity technique
To detect and examine exoplanets. Transit technique involves measuring periodic decrease in brightness of star as planet moves in front of it relative to us. Transit depth radius^2 planet/radius^2 star. Large planet small star deepest transit, easiest to detect. Radial velocity using doppler shifts in spectrum.
Galaxy properties, sun and other stars
Sirius B, white dwarf, similar size to earth. Antares has diameter 2AU, massive! Stars from 10% size of sun to 100 solar masses. Luminosity from 1000thof solar luminosity to a million times brighter. Surface temps a few 000 degrees to tens of thousands
Galaxy size
tens of thousands of light years in diameter. Milky way 10^5. 10^11 stars in milky way (100 billion). Andromeda galaxy 2.5 million light years away
Extragalactic
Outside our galaxy
Types of Galaxy
Spiral, Elliptical, irregular. Spiral can have bars. Also between the 2 main types are Lenticular (lens shaped)
Galaxy classification
Elliptical by shape, Spiral by how tightly spiral arms wound
Hubble’s Tuning Fork Classification
Elliptical: E and number 0-7, eg E3. Lenticular SBO (with bar), SB. Normal Spirals S, SB (With bar) and lower case letter denotes how much central bulge dominates and arms tightly wound. eg Sa, SBa - bulge dominates, arms tightly wound. Sc, SBc - bulge small, arms open
Blueshift and redshift
Using doppler effect with light waves, if star moving towards observer, wavelengths shorter, frequency higher, the light is blueshifted. If star moving away, wavelength increases, frequency decreases, the light is redshifted.
Galaxy rotation and kepler
Orbital radius increases, by keplers laws the speed decreases. BUT speed seems to increase the further out from the centre the stars get - DARK MATTER
Dark matter
More mass than all stars and gas combined. Transparent, neither emits nor absorbs light - no electromagnetic forces as light is electromagnetic radiation. DM particles collect together in halos, but not form planets etc as only weak interaction. Could make up 80% of all matter
Dark matter halos
DM particlescollect together in halos - possible stars exist within larger halos. So mass not at centre of galaxy as we thought but distributed evenly, hence only matter within an orbit contributes to gravitational force. As orbital period constant for any orbital radius, stars furthest away move faster (unlike planetary orbits)
