Components of the universe

Question 1

Astronomical unit

Answer 1

Distance from earth to sun, approx 150 million km

Question 2

Light year (ly)

Answer 2

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)

Question 3

Speed of light

Answer 3

3.00 x 10^8 ms^-1 So 300 million metres per sec

Question 4

Angular size and angular resolution

Answer 4

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

Question 5

Angular size, actual size and distance

Answer 5

angular size (degrees) = 57 x (actual size/ distance observer to object)

Question 6

Gravitational wave detection

Answer 6

Vibrating space, information encoded in vibrations

Question 7

Semimajor axis

Answer 7

Largest distance from centre of ellipse to orbit

Question 8

Eccentricity of an object’s orbit

Answer 8

Decree of elongation of orbit (in other words how elliptical). e=0 (circular obit) - close to 1

Question 9

Kepler’s laws

Answer 9

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)

Question 10

Kepler’s third law

Answer 10

The square of the orbital period of a planet is proportional to the cube of the semimajor axis of its orbit

Question 11

Gradients of the graphs with a^3 against p^2 for 2 different systems also gives ration of mass of central body.

Answer 11

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

Question 12

Extrasolar planet (exoplanet)

Answer 12

Planet orbiting stars other than the sun (eg proxima b orbiting proxima centauri, our nearest star outside our solar system)

Question 13

Goldilocks zone (planets)

Answer 13

Far enough from star to be not too hot, close enough to be not too cold…so life more likely

Question 14

Transit technique and Radial velocity technique

Answer 14

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.

Question 15

Galaxy properties, sun and other stars

Answer 15

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

Question 16

Galaxy size

Answer 16

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

Question 17

Extragalactic

Answer 17

Outside our galaxy

Question 18

Types of Galaxy

Answer 18

Spiral, Elliptical, irregular. Spiral can have bars. Also between the 2 main types are Lenticular (lens shaped)

Question 19

Galaxy classification

Answer 19

Elliptical by shape, Spiral by how tightly spiral arms wound

Question 20

Hubble’s Tuning Fork Classification

Answer 20

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

Question 21

Blueshift and redshift

Answer 21

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.

Question 22

Galaxy rotation and kepler

Answer 22

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

Question 23

Dark matter

Answer 23

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

Question 24

Dark matter halos

Answer 24

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)

Question 25

Dark energy

Answer 25

Universe expanding faster, energy must come from somewhere. Universe 69% dark energy, 26% dark matter, 5% atoms.

Question 26

Galaxy clusters

Answer 26

Milky way part of local cluster (more than 54 galaxies), in turn part of virgo supercluster, in turn part of…etc. Galaxy clusters interconnected, like spider web