physcics - topic 7 space

What is a galaxy?

• collection of stars, rocks and gases pulled together by gravity

• We live in a cluster of galaxies called andromeda

What are stars?

Massive balls of hydrogen gas

Our sun is about 5 billion years old

Dwarf planets?

• five named ones

• Not full planets because they are not completely spherical nor have they cleared the orbital path of other objects

Asteroids + comets?

• asteroids are very small rocks

• Comets are icy rocks - often outside of solar system

Terrestrial planets

• mercury, Venus, earth and mars

• Rocky planets

• Solid surfaces

• No rings

• Few moons

• Quite small

Jovian planets ?

• Jupiter + Saturn (gas giants)

• Uranus + Neptune (ice giants )

• Gas giants mostly helium and hydrogen

• Ice giants mostly rock + ice

• no solid surface

• Many moons

• Ring systems

• Immense in size

What is a satellite?

• any object that orbits a plant

• Natural = moon

• Artificial = space station

Which planets don’t have moons?

Mercury + Venus

Earth’s artificial satellites?

• over 12,000

• For communication, security and weather

Low earth orbit

• Where most satellites are launched

• 300 - 2000km

• Often used for observation

Polar orbit?

Earth rotates beneath them but they are fixed, see most of planet each day

Used for weather

Geostationary satellites?

• travel at diced speed that keeps them directly above a fixed point on equator

• To Sattelites

• Orbit at same rate as earth

• 24 hours per orbit

Why does orbit occur?

Due to gravitational attraction between objects

Speed during orbit?

• speed stays constant

• No friction as no particles

• Direction is constantly chaninging so so is velocity (speed in a direction)

What does orbital speed depend on?

• radius from centre of plant/sun

  orbital length = circumference

Radius of earth?

6370 km

Relationship between orbital speed and+ orbital radius?

• inversely proportional/ inverse square relationship

What are stars powered by?

• nuclear fussion - binding two hydrogen nuclei into helium

• Releases lots of energy

Phases of star life?

• formed

• Relatively stable period

• Fade or explode

How are stars born?

• nebula/ stellar nurseries - areas of hydrogen gas and dust (dust from older dead stars, hydrogen from beginning of universe)

• Nebula collapses due to change in gravity - particles pulled tighter , faster + denser

• Collapses continues - end up with a dense rotating sphere or gas + dust (pressure + temp increases)

What is a protostar?

• dense hot sphere from nebula collapses

• core has very high temp + pressure

Core of protostar?

• gravity pulls in

• Pressure pushes out

• Balence one another

What happens when pressure gets too high?

• the forces between hydrogen nuclei are overcome so they collide

Nuclear fusion?

• the process of merging small nuclei into larger nuclei with release of energy

• Hydrogen isotopes—> fusion —> helium + neutron (load of energy)

• Turns protostar into main sequence star (emits light)

• Bigger star goes through fuel faster

Life cycle of stars like sun?

• main sequence star

• Evolve into red giant (size decrease pressure increase)

• Fuse helium (star expands + cools)

• Lawyers drift off to form planetary nebula

• Left with cor (white dwarf) - very hot and dull

• Cools to black dwarf

Life cycle of stars much bigger than sun ?

• evolve to red super giant

• Layers of fusion (every enemy up to iron is created here)

• Into a supernova (layers collpase, hit core and ricochet off)

• Every element past iron made here

• Neutron star (v heavy, small and dense)

• If neutron to big or dense it will collapse On itself and become a black hole

Violet light?

• short wave length

• High frequency

Red light

• long wave length

• Low frequency

Spectrum?

• what we get when we split white light into its colours

Absorption lines?

• black lines on spectrum

• Created as gases in star absorb the visible light

• Frequency of lines are very specific so relate to particular element

Hydrogen lines?

Used to compare stars as all stars contain hydrogen

Red shift?

• hydrogen line shifts towards red

• Star moving away from us - wavelength increases and frequency decreases

• Further away = more red shift

• Also applied to galaxies

Red shift in galaxies?

• light from almost all galaxies is red shift so they are all moving away

• Shows universe is expanding

Hubbles law?

• distance of a galaxy from the Milky Way us directly proportional to it’s velocity

• Further away = faster

Big Bang theory ?

• all of matter in universe occupied the same very small region of space in distant past ( 13.8/14 billion years ago)

• Universe wouldn’t habe been very hot + dense

• Expanded very quickly, cooled down to from matter as we know it

• Gravity pulled all matter together

Evidence for big bang?

• cosmic microwave background radiation / cmbr

• Early universe = high energy + short wavelength (gamma)

• Current universe = wave lengths expanded with universe

• Also shows universe was very hot and has cooled

Dark matter?

• universe expanding at faster rate, galaxies are larger than what we think they should be

• Caused by dark energy / matter, reacts with nothing but gravity