Waves
We are all familiar with waves; from ripples on the surface of a pond to the swell of the ocean. A wave is just a regular vibration that travels through something, like air or water.
Unlike sound, light waves can travel through nothing, like the vacuum of space. This means that the light coming from stars, and all other objects in space is able to reach us here on Earth.
Distance
Measuring distances in astronomy is difficult but crucial. We need to know how far away objects are to look at the differences between them. Two objects can look different but be very similar, with one further away than the other. This can make them challenging to study.
- How do we measure distance?
Knowing the distance to objects in space is important. However, measuring it is also very hard—you can't just use a ruler! Astronomers have created a range of ways to measure the distance to objects in space.
Electromagnetic Spectrum
This light that we see is just one small chunk of light which is made by stars. We often call the small range of wavelengths our eyes can detect, optical, or visible light.
- Properties of each Electromagnetic Wave
Moving through the electromagnetic spectrum we go from short to long wavelengths and the frequency of the waves gets smaller. We go from high-energy to low-energy.
Wave-Particle Duality
To understand what happens to light when it reaches a mirror, we can say that photons bounce off the surface of the mirror. This treats the light as a particle like a ping-pong ball bouncing back. If we pass light through 2 holes then at the other side of the holes we see it interact like waves on the surface of a pond.
When we take a photograph on a modern camera, or on a telescope camera, we count these photons. The more we count the brighter an object is - we call this measurement the flux.
Spectra
Even though light often looks white, it is made up of lots of different colours all added together.
Astronomers often want to know exactly what colours of light there are coming from a star or galaxy. To measure this, they use an instrument called a spectroscope. These have prisms, or gratings, inside them which separate the light. They then record the data.
Light
When we talk about light we usually mean the light we can see with our eyes. This is also called visible or optical light.
- How does light travel?
For us to see, light must travel from a light source to our eye. The light we see on Earth travels in straight lines.
Anything in the path of light has an effect on what we see. For example, a window is transparent – this means that the light can pass straight through it.
Particle
- Sub-atomic Particles
Particles come in different sizes – some are so small that they make up atoms - like electrons. We call these sized particles “sub-atomic”. These also include protons and neutrons.
But these are made of even smaller particles called quarks!
Particle physics is the branch of science which studies these small particles. They include photons, the particles which also make up light.
Momentum
If an object is moving, it has momentum. This is what keeps an object moving in the same direction. The more momentum something has, the harder it is to change its direction or bring it to a stop.
So we can work out an object's momentum using the equation:
Momentum = mass × velocity
During an explosion or collision, the total momentum is conserved. This means the total momentum before the event is equal to the total momentum after the event. This is useful for studying collisions in space or stellar explosions.
Semiconductors
Semiconductors are an important part of CCD cameras (Charge-coupled Devices). They help to convert light into a current in the technology.
- n-doping
Here, silicon (Si) is doped with a material like phosphorus (P). This replaces some silicon atoms in the crystal.
The silicon bonds with the phosphorus but leaves behind an extra electron. This is loose inside the crystal and can be freed easily. This lets it conduct electricity.
The electrons that are freed have a negative charge, so the process is called n-doping.
Gravitational Lensing
Space is not flat. It is 3D, and we say that everything in it is held together on an imaginary surface we call spacetime. The idea of spacetime was put forward in Einstein's theory of relativity.
- How does Gravitational Lensing happen?
Lensing happens when light from directly behind a massive object, from our line of sight, can be bent around it. We call this gravitational lensing, and it is a way to see an example of the theory of relativity.