8.1-8.3 - Astrophysics Flashcards
What is the universe
A collection of billions of galaxies
What is a galaxy?
A large collection of billions of stars, stars are astronomical objects such as the sun
What is a solar system?
A collection of stars
What is gravitational field strength?
The strength of gravity on a planet or moon. The larger the mass of a planet the greater its gravitational field strength. The larger the radius of a planet the smaller the gravitational field strength higher the gravitational field strength means larger attractive force towards the centre of that planet or moon.
What is weight?
Weight is the force acting on an object due to gravitational attraction and because of weight objects will stay firmly on the ground and satellites in orbit.
What is gravitational force?
Planets and comets travel around the sun Moons and satellites travel around planets. For this to happen forces must be applied to them between any two objects there is always a force of attraction. This is due to the masses of the objects.
How does mass effect force of attraction?
The gravitational attraction between two objects with small masses us tiny only when one or both objects have very large mass is the force attraction obvious . The Sun is massive containing 99% of mass of the solar system it is the gravitational attraction between this as and each of the planets that holds the solar system together.
How does a body start to orbit?
In order to orbit a body such as a star or planet there has to be a force pulling towards that body, gravity provides this force. The gravitational force exerted by the larger body on the orbiting object is alwasy attractive therefore the gravitational force always acts towards the centre of the larger body the gravitational force will cause the body to move and maintain in a circular path. Planets orbit the sun, moons orbit planets comets orbit the sun.
What is a satellite?
An object that orbits a planet
How do Moons orbit?
Moons orbit planets in a circular path, some planets have more than one moon the closer the moon is to the planet the shorter the time it will take to orbit.
How do comets orbit?
As comets approach the sun, its speed increases as it moves futher away it speeds decreases. Not all comets orbit in the same plane as the planets and some do not even orbit in the same directions
How is orbital speed calculated?
2pie x the orbital radius
Orbital speed equation
speed= distance / time
What does the colour of a star tell us?
The tempreture of the star
What colour does a very hot star emit?
A very hot star emits more blue and therefore looks blue
What colour does a medium star look like?
A star like our sun is yellow
What colour is a cooler star
A cooler colour star is red.
What do objects that are warm emit
Infrared heat.
What do extremly hot objects emit
visible light.
What does the brightness of a star depend on?
The distance the star is from earth and what the star is made from and what kind of nuclear reactions are taking place
Explain the nebula stage of a star (1st stage)
Stars are formed from large clouds of dust and gas particles that are called nebulae. These particles are drawn together over a very long period of time by gravitational forces. These particles are pulled together so tightly that there is a very large increase in tempreture and pressure. As a result of this, nuclear fusion reactions begin. Hydrogen nuclei join together to make a larger nuclei and huge amounts of energy in the form of heat and light are released. The incredible hot ball of gas formed is a prostar.
Explain the Prostar stage of a star (2nd stage)
The forces of gravity within a nebula pulls the particles closer together until it forms a hot ball of gas known as a prostar. All of the particles are pulled together tightly then the density of the prostar will increase. This will result in more frequent collisions between the particles because the partciles are being pulled together so tightly this causes the tempreture to increase
Explain the Main sequence stage of a star (3rd stage)
A main sequence star forms once the prostar becomes hot enough so nuclear fusion will occour within its core. The hydrogen nuclei will fuse to form helium nuclei every fusion releases heat energy which keeps the core hot. Thermal expansion from fusion reactions occours within its core due to the fusion and the force of gravity keeps the star of equilibrium. The inward force due to gravity is equal to the outward pressure force which results from the expanding hot gases inside the star.
Explain the red giant stage of a star (4th stage)
After several billion years when the most of the helium has been fused because the hydrogen has run out because of this fusion reactions in the core will start to die down. This will cause the core to contract and heat up and the star will change colour it will emit more blue and white light the core has shrunk because of the inward force due to gravity will become greater than the outward force due to the pressure dying down a new series of reactions will then occour around the core for example helium nuclei will undergo fusion to form beryllium as the core shrinks more reactions will cause the outer part of the star to expand it will become a red giant and because it is red its surface will start to cool down