Space

Kepler’s first law

Orbit in ellipse with sun at one focus

Kepler’s second law

Planets move faster when closer to sun, sweeps out equal areas of orbit in equal time

Kepler’s third law

Further away = longer orbital period ; p² = a³

Galileo’s theory of relativity

Can’t perceive constant motion; free motion is constant in speed and direction

Newton’s first law

Object moves at constant velocity unless net force acts on it

Newton’s second law

F = ma (rate of change of momentum)

Newton’s third law

Every action has an equal and opposite reaction

Two-body problem solution

Two orbiting objects orbit their shared centre of mass

Tides causes

Moon-side: moon attracting water away from earth

Far side: moon attracting earth away from water

Tidal friction effects

Slows earth’s rotation and pushes moon away from earth

Nebular hypothesis

Theory for how the solar system formed (spinning disc, gravity)

Comets found in

Kuiper belt: formed there, 30-110 AU

Oort cloud: ejected by Jovians, 50k AU

Giant impact theory explains

Earth’s moon, Venus’s backward rotation, Uranus’s axial tilt

Lithosphere

Rigid outermost layers of differentiated planet: crust and top layers of mantle, split into tectonic plates

P waves

(Pressure) shake backwards and forwards, can pass through Earth’s core

S waves

Shake side to side (perpendicular to direction of travel), don’t pass through the core

4 processes shaping planet surface

Impact craters, volcanism, tectonics, erosion

2 principles of special relativity

Laws of physics are universal; speed of light is constant

Time dilation

Fast moving POV experiences less time relative to stationary observer

Length contraction

Fast moving POV measures distances as shorter relative to stationary observer

Mass increase

As momentum = m * v and velocity cannot exceed c, relativistic mass increases

Ellipse semimajor axis

Half of major (long) axis

Perihelion

Focus of elliptical orbit at the star

Aphelion

Focus of elliptical orbit where there is nothing

Momentum

Mass * velocity

Lunar maria

Smooth, dark, less cratered regions of the moon created by floods of runny lava

Orbital resonance

Asteroids with a period of a regular fraction of Jupiter’s, which experience regular gravitational tugs and are slingshotted away

Why didn’t the asteroid belt form a planet

Tidal forces from Jupiter stopped it accreting

Comet coma

Atmosphere coming from heated nucleus

Comet plasma tail

Gas escaping from coma, pushed by solar wind

Comet dust tail

Dust escaping from its gravity, pushed by photons

Telescope angular resolution

Minimum angular separation that can be distinguished; limited by diffraction limit, which is 1/telescope diameter

Lorentz factor

Radiative zone

Gamma rays/photons travel at random by radiation, taking 100 000 yrs

Convection zone

Hotter regions rise and cooler ones sink, energy carried as heat in gas

Photosphere

Cooled to 5800K, photons live at visible energies; visible surface of sun

Granulation

1000-2000km across, caused by convection patterns

Corona

Higher temp (1 million K), extremely low density, origin of solar x-rays

Solar wind

Protons and electrons evaporated from the corona, replenished from below, speed = 400-800 km/s

Heliosphere

Extent of solar wind; about 100 AU, ~3x past Neptune

Star types hottest/bluest to coolest/reddest

O B A F G K M

Giants

Moderately bright, cooler than the sun, 10-100x R_sun

Supergiants

Extremely luminous but still <10 000K

White dwarfs

Very dim but hot, 0.1 R_sun/earth-sized

Open cluster

100s-1000s of stars, loosely bound, usually young as old ones get pulled apart

Globular cluster

100 000s to millions, tightly bound, very dense in core, often old

Pulsar

Rotating neutron star, with beams of radiation from the magnetic poles

Spiral galaxy disc

Flat, contains spiral arms which are site of new star formation, plus gas and dust

Spiral galaxy bulge and halo

Spherical, contain globular clusters

Elliptical galaxy

Round or flattened balls, mostly old stars

Cepheids

Variable stars with tight relationship between oscillation period and absolute luminosity; allows absolute luminosity to be measured and distance found

White dwarf binary (type 1a) supernova

Explosions always emit the same amount of energy; allows distance to be found

Hubble’s law

The further away it is, the faster it is moving away from us

Galaxy group

1-5 large galaxies, various satellite dwarf galaxies

Galaxy clusters

10s-100s of large galaxies, 1000s of dwarfs; the most massive gravitationally bound objects

Fine-tuning problem

Universe appears precisely optimised for life

Strong anthropic prinicple

Universe was designed with intelligent life in mind

Weak anthropic principle

Intelligent life may be however unlikely, we are a product of selection bias — the only universe we can inhabit is one that supports intelligent life