astronomy

galaxies

a gravitationally bound systems of gas, dust and millions or billions of stars and solar systems

shapes

• elliptical

• spiral

• barred (spiral)

• irregular (anything that dones’t fit above

milky way (our galazy)

• our systems is on the Orion Arm

• closest galazy: Andromedo

• 200-400b stars

• 100,000 lights years in diameter

solar systems

gravitationally bound systems of the Sun + the objects orbit it

constellations

group of stars as seen from earth that appear to form a familiar shape

contellations examples

• many different cultures have own stories/ diff meanings to it

• e.g emu in the sky. the emu indicate various seasonal activities like egg-laying season

stars

a luminious body of gas that shines due to nuclear fusion

absolute magnitude

how bright a star actually is

• if it was 10 parsecs from Earth

apparent magnitude

how bright a star appears from Earth

• affected by distance from earth

more negative=

brighter

more positive=

dimmer/ less brighter

small stars

e.g neutron stars 20-40k diameter

large stars

e.g supergiants 1500 x larger than our Sun

colour of stars

determined by temperature

hottest stars

blue/violet

coller stars

red

nuclearfusion

• nuclei fuse (atoms joins together) → create energy

• light atoms (e.g H) joins + become heavier atoms (e.g He) ‘H+’H=2He

hertz- russel diagram

shows relationship between stars tempoerate + brightness (luminosity. shows how they change during lifestyle

x-axis=temperature

->left is hot

->right is cooler

y-axis=luminosity(absolute magnitude)

->bright stars at the top

->dimmer stars at bottom

On the diagram stars are ranked from bottom to top in order of decreasing magnitude (increasing brightness) and from right to left by increasing temperature

bigger stars →

hotter + brighter

• more gravity

• more nuclear fusion → releases energy

Doppler effect

when objects are moving, the waves (sound/light) are produced by that object will be either lengthened or shortened due to their motion

blue shift + red shift

light from stars occurs when light waves from stars

blue: object approaching

red: object receding

blue shift

light from stars moving towards us will be compressed (blue shifted) + more blue than actual, wavelengths get shorter

red shift

light from, stars moving away from us will be stretched (red shifted) and more red than actually is, wavelengths get longer

moving sound source

long wave-length: low frequency

small wavelength: high frequency

electromagnetic spectrum description

small wavelegnths= high energy, higher frequency

long wavelegnths= lower energy, lower frequency

why are most galaxies red shifted

move away from us, universe is expanding → refers to big bang theory

sequence of their life

stars start bottom right of main sequence and move upwards and left during their life

big bang theory

an explanation of how the universe was created

what does the theory say?

-13.7b years ago universe started as a singularity (single point)

what does the theory mean now

• explosion → universe started to expand and cool

  • universe is explanding

cosmic mircowave backgroun radiaiton

left over radiation for big bang

• radiation appears red shifted

→ moving away

→ universe is expanding

what is the universe made of

hydrogen (74%) + helium (25%)

formation of elements

hydrogen formed first

other elements form via nuclearfusion

the age of stars

• some are 13b years old

• universe has to be older

  → big bang happen 13.7b+ years ago

life cycle of stars

nebula → protostar → main sequence star → red giant → white dwarf→ black dwarf. → red super giant → supernova → neutron star → black hole

birth of a star stage 1- nebula

a star is born in a huge, cold cloud of gas and dust called a nebula

birth of a star stage 2- nebula contracts

nebula slowly contracts under own gravity and clump of matter forms inside cloud

birth of a star stage 3- clump heats up

gravity continues pulling in more matter + clump collapse inward, becomes dense and compressed begins to heat up

birth of a star stage 4- star shines

core of collapsing clump so hot + compressed nuclear reactions start, hydrogen fuses form helium releasing energy = sun to shine

death of a star stage 1- red giant forms

hydrogen used up → helium core collapse and outer layer expands and cools. star shines less brightly = red giant. death of a star after the red giant shape depends on size of star

death of a star stage 2- beyond a red giant

small starr → massive star → really massive star

death of small star

becomes red giant, outer layer drifts. core reamins = white dwarf, cooles and eventually stops shining and becomes black dwarf

death of a massive star

becomes red giant, nuclear reactions in helium core continue and form other elements around iron core. collapse core= explosion → super nova. remains form tiny, very dense neutron star.

death of a really massive star

red giant stage, nuclear reaction create iron core which explodes as supernova and forms neutron star. difference= core of neutron star collapses further and results in black hole

black hole

• place and space where gravity pulls so much that lught can not get out

• range in size: 1 atom- 1 millions suns in diameter

• every large galazy contains a supermassive black hole at its centre