ASTROPHYSICS Flashcards
(40 cards)
1
Q
The universe?
A
-A galaxy is a large collection of billions of stars.
2
Q
Our galaxy is called the…?
A
-Milky Way
3
Q
Our solar system is…?
A
-Our Solar System is a collection of 8 planets orbiting a star called the Sun.
4
Q
Order of planets from the sun outwards?
A
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
5
Q
What do planets, asteroids and comets orbit?
A
-Orbit the Sun
6
Q
What do moons orbit?
A
-Moons orbit planets
7
Q
What causes planets (e.g, sun and planets) to orbit?
A
-It is the gravitational force between objects
8
Q
Orbits can be…?
A
-Orbits can be circular or elliptical.
9
Q
Moon and planets have orbits which are…?
A
-Circular or slightly elliptical
10
Q
Comets have … orbits?
A
-Elliptical orbits.
11
Q
Moon definition?
A
- A celestial body (or object) that orbits a planet in a circular orbit. It is a natural satellite of a planet and the one that orbits Earth is just called ‘The Moon’
- Moons orbit planets and normally have circular orbits.
12
Q
Planet definition?
A
- A celestial body that orbits a star. There are 8 planets that orbit the Sun, along with dwarf planets and other objects
- Planets have slightly elliptical orbits(i.e. The inner planets are almost circular, but the outer planets are more oval).
13
Q
Comet?
A
-A celestial body of ice and dust that orbits the Sun in a very elliptical orbit. They release a tail of gas as they warm up when approaching the Sun
14
Q
Solar system definition?
A
- The Sun, together with the group of celestial bodies that are held by its gravitational attraction and orbit around it; either directly or indirectly.
- It is made up of the Sun, 8 planets, their moons, dwarf planets, asteroids, comets, gas and dust.
15
Q
Galaxy?
A
-A system of millions or billions of stars, together with gas and dust, held together by gravitational attraction. Our galaxy is called the Milky Way.
16
Q
Universe?
A
-The whole of space and all the stars, planets, and other forms of matter and energy in it.
17
Q
Gravitational force?
A
- There is an attractive force between any two objects that have mass. It is called the gravitational force.
- The greater the mass of the two objects and the closer in distance they are – the greater this force is.
18
Q
What two factors affecte the gravitational attraction between objects?
A
- mass
- distance
19
Q
If mass increases, the force of gravity…?
A
Increases
20
Q
If distance increases, the force of gravity…?
A
Decreases
21
Q
Gravitational force key facts?
A
- The gravitational force causes the planets to orbit around the Sun, as if there was an invisible ‘rope’ attached between both, like a hammer thrower spinning around.
- The gravitational force always acts towards the centre!
- The Sun has 99% of the mass of the Solar System, so causes planets to orbit around it – and the closer a planet is, the stronger the pull and the more curved and circular the path is.
- The further away the planet from the Sun, the longer it takes to complete one orbit. This is because the gravitational force is less, so its orbital speed is less.
22
Q
Comets explanation?
A
- Comets are large rock-like pieces of ice that orbit the Sun. They have very elliptical (elongated) orbits that means they are travel close to the Sun and then travel out to the very edge of the Solar System
- Comets speed up as they travel closer to the Sun.
23
Q
Artificial satellites?
A
- Artificial satellites can have circular or elliptical Earth orbits
- Many satellites are in a very high orbit and are used for communication purposes, while others in low orbits are used for weather and mapping.
- Geostationary satellites take 24 hours to orbit around the equator (the same time as the Earth rotates) so they appear in the same place in the sky.
24
Q
Gravitational field strength?
A
- The gravitational field strength (g) of a planet or moon shows how strong the gravitational force is.
- On Earth g = 10 N/kg, but on the Moon it is only ❤️1.6 N/kg❤️
- On a larger planet, like Jupiter, g = 23 N/kg.
- you weigh differently on different planets or out in space (even though your mass stays the same)
25
Weight equation?
- weight = mass x gravitational field strength
| - W = mg
26
Orbital speed equation?
-speed (v) = distance (s)
——————-
time (t)
-2 x π x orbital radius
——————-
time period
-v = 2πr T
27
Orbital speed explanation?
- The orbital speed (v) of planets, moons or even artificial satellites orbiting the Earth, depends on the orbital radius (r) and the time period (T) of one complete orbit.
- The circumference of a circle = 2 x π x r and that is the distance the planet travels in one complete orbit.
28
Star classification by colour?
- The colour of stars depends on the frequency of the light emitted – which depends on their surface temperature.
- Stars can be classified by their colour.
* Hotter stars give out light at higher frequencies.
* Cooler stars give out light at lower frequencies.
-This allows them to put into different spectral classes.
29
The birth of a star?
-A planetary system (such as our Solar System), is created after the birth of a star (like our Sun).
30
Nebula?
- a cloud of gas and dust
- all stars are formed from gas and dust which slowly come together due to the force of gravity
- the birth place of stars
31
Clouds of gas and dust continue to collapse...?
- The force of gravity makes the clouds become more dense and much hotter!
- It spins faster and faster and becomes a flat disc
- At the centre a protostar is formed – not quite hot or dense enough to ignite and become a full star!
32
How is a star born?
- when it is extremely hot and dense – nuclear fusion begins (hydrogen nuclei fusing to form helium nuclei) and a star is born!
- Large amounts of energy are given out and produce an outwards radiation pressure.
- The remaining gas and dust is blown out to the edge of the solar system leaving the planets behind.
—The star is now a MAIN SEQUENCE STAR!
33
A stable main sequence star?
- This stage can last millions or billions of years
- It is very stable and maintains a similar size because the inwards force of gravity is balanced by the outwards force caused by the thermal radiation pressure
- However, after millions or billions of years, what happens once the star starts running out of hydrogen ‘fuel’?
- It depends on its mass (or size)
34
The life history of a small star? (E.g, our sun)
1. Gas and dust (nebula)
2. Protostar
3. Main sequence star
4. Red giant
5. White dwarf
6. Black dwarf
35
Main sequence -> red giant?
- Fusion of H to He stops
- Outward radiation pressure reduces
- Core collapses under gravity
- Core gets hotter
- Pushes the outer layer of gas outwards
- The core is now white hot.
- As the outer layers expands, they cool - making the star appear as a RED GIANT
36
Red giant -> white dwarf
- The core keeps collapsing and getting hotter.
- The outer shell keeps expanding and cooling
- Fusion of heavier and heavier elements takes place – up to IRON
- Fusion of iron does not release energy
- Fusion stops.
- The shell is so far away from the core that gravity cannot hold it in place and it simply drifts away leaving the white hot core behind
- Over millions of years, this small, but hot, WHITE DWARF slowing cools and eventually becomes a cold BLACK DWARF
37
The life history of a large star?
1. Gas and dust (nebula)
2. Protostar
3. Main sequence
4. Red super giant
5. Supernova
6. Neutron star and black hole
-larger stars burn brighter and hotter but die younger
38
Main sequence -> red supergiant -> supernova
* The same process as a small star happens
* However the core is much larger, so when the outward pressure stops completely, the core has enough gravity to pull the outer layers back in
* These outer layers accelerate at speeds up to about a quarter the speed of light!
* The collision with the core is so great, the gases rebound back out in an explosion (a SUPERNOVA)
* The strong force of gravity at the collapsing core crushes all the electrons and protons together forming nothing but a dense ball of neutrons – a NEUTRON STAR - giving off X-rays and gamma rays.
* All its mass is probably packed into a diameter of less than 10 km!
39
Neutron star and black holes?
* If the remaining core mass is over 3 times the mass of our Sun, the core will not stop as a neutron star. The neutrons are unable to prevent further collapse due to gravity into an extremely small and dense core.
* Gravity is so strong, no radiation, including light, can escape – you now have a BLACK HOLE.
40
Stars and supernova, birthplace of the elements?
- All the elements – up to iron – are produced inside stars during nuclear fusion.
- Helium is produced most of the time, but heavier elements such as carbon, nitrogen, oxygen, silicon, calcium and eventually iron, are produced in the last stages of a large star’s life, as it frantically tries to fuse any elements at higher temperatures/pressures, as it runs out of fuel.
- Elements heavier than iron cannot be produced by fusion, but are created during a supernova, where there is enough energy to fuse these heavy elements together!
- We are all made up of star dust from the heart of a star or an exploding supernova!
