Astrophysics Flashcards
What is the Universe?
Large collection of billions of galaxies
What is a Galaxy?
Large collection of stars
What are Planets? Many Vampires Eat Mothers Joyfully So Undress Now
•Large objects that orbit the Sun in circular orbits •There are 8 planets : Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
What are Dwarf Planets and give an example?
- Plant like objects that aren’t big enough to be planets
* E.g. Pluto
What are Moons?
- Orbit planets with circular orbits
* Type of Natural satellite
What are Artificial Satellite?
- Ones humans have built
* Orbit Earth in circular orbits
What are Asteroids?
- Lumps of rock and metal that orbit the Sun
* Found in asteroid belt
What are Comets?
- Lumps of ice and dust that orbit the Sun
- Orbits are highly elliptical
- Some travel from near to Sun to outskirts of our solar system
How does Gravity provide the Force that creates Orbits?
- Object travelling in circle = changes direction = accelerating = there’s a force acting on it
- Centripetal force causing it - causes object to change direction because it’s moving
- Object keeps accelerating towards what its orbiting but velocity travelling in circle
- Gravitational force - gravitational attraction of Sun keeps planets + comets in their orbits
What happens the Closer you get to a Star or Plant?
- Stronger the gravitational force is
* The faster you need to go to remain in orbit
What are the different types of Orbit?
- Moons + planets are slightly elliptical
* Comets have very elliptical elongated orbits with the Sun at one focus
When do Comets travel faster?
- Nearer the sun
* Because increased pull of gravity makes it sped up the closer it gets to the sun
What are Geostationary Satellites and what are they Useful for?
- Artificial Earth satellites have orbital period of one day
- Useful in communications because they’re always over same part of plant
What is a Nebula?
Stars initially form from a cloud of dust and gas called nebula
What is a Protostar?
Force of gravity pulls gas/dust together to form a protostar
How is a Star Born from a Protostar?
- Temp rises as star gets denser and more particles collide
- High enough temp = hydrogen nuclei undergo nuclear fusion to form helium nuclei
- Give our a lot of energy, keeping core of star hot
- Star is born
What is a Main Sequence Star?
- Star enters long stable period - outward pressure caused by thermal expansion balances the force of gravity pulling everything inwards = main sequence star
- Heavier star = shorter its time on main sequence
What is a Red Giant and Red SuperGiant?
- Hydrogen in core runs out + force is larger than pressure of thermal expansion
- Stars compressed, until it’s dense + hot so energy makes outer layers of Star expand
- Red giant = smaller star
- Red supergiant = larger star
- Red because surface cools
What is a White Dwarf?
- Small star becomes unstable + ejects outer layers of dust + gas
- Leaves behind hot, dense solid core = a white dwarf
What is a SuperNova?
- Big stars glow brightly again as undergo more fusion to make heavier elements
- They expand + contract several times
- Balance shifts between gravity + thermal expansion
- They explode in supernova
What is a Neutron Star and a Black Hole?
- Exploding supernova throws outer layers of dust + gas
- Leaves dense core = neutron Star
- If Star is massive enough, it will collapse and become a black hole - super dense
What is Sequence of Star that has a Low Mass?
- Nebula
- Protostar
- Main sequence star
- Red giant
- White dwarf
What is Sequence of Star that has a High Mass?
- Nebula
- Protostar
- Main sequence star
- Red supergiant
- Supernova
- Neutron Star or black hole
What does a Stars Brightness depend on?
- It’s size + temperature + distance from Earth + absolute magnitude
- Bigger star + hotter star + closer to Earth + lower absolute magnitude = brighter
What is Absolute Magnitude?
- Measure of how bright a star would appear if it was a fixed distance from Earth
- Used to compare brightness of stars
What is the Hertzsprung-Russel Diagram?
- Graph of absolute magnitude against temperature for stars
* Groups that correspond to different periods in stars life cycle
Where are Red Giants or Red SuperGiants on the Hertzsprung-Russel Diagram?
- Top right
* They’re cool, Large, bright
Where are White Dwarfs on the Hertzsprung-Russel Diagram?
- Bottom left
* They’re hot, small, dim
Where are Main Sequence Stars on the Hertzsprung-Russel Diagram?
- Whole of graph diagonally from top left to bottom right
* Brighter Star = higher temp
What is the Red-Shift?
If light source moving away from you, light it emits will appear to be shifted towards the red end of EM spectrum
What is the evidence that light from galaxies are Red-Shifted?
- Different elements absorb different frequencies of light
- Light passed through sample of element, pattern of dark lines produced
- When look at light from distant galaxies we see same patterns at lower frequencies than they should be
- Patterns shifted towards red end of spectrum = red-shift
What does measurements of the red-shift suggest?
- All distant galaxies are moving away from us quickly
- More distant = greater red shift = show bigger observed increase in wavelength = moving away faster
- Whole universe is expanding
What is the Cosmic Microwave Background (CMB) Radiation and what is it Evidence of?
- Scientists detect low frequency microwave radiation coming from all directions + all parts of the universe
- Background radiation is evidence for initial Big Bang
- As universe expands + cools - background radiation cools + drops in frequency
What is the theory of a Big Bang?
- All matter in universe occupied at single point
- This tiny space was dense + hot
- This single point ‘exploded’ = Big Bang
- Space started expanding, and explosion is still going on
- CMB radiation is leftover energy of initial explosion
