Light

Observing Techniques

Optics

Optics is an area of physics which looks at how light behaves and how we can observe it.

This usually involves using mirrors and lenses to magnify, focus, and direct the path of light.

There is an illustration of a bulging lens on the left. A dashed line runs through the centre across the image. Two red parallel lines hit the lens towards the top and bottom and then become diagonal, crossing paths at a point labelled "F" some distance after the lens. This distance is noted with a black arrow labelled "f'". — Light (red lines) passing through a convex lens. The point at which the light meets (F') is called the focus. The distance from the lens to the focus (f') is called the focal length.

How Telescopes Work

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.

Ripples on the surface of still water, caused by an object or disturbance, spreading out in concentric circles

This work by Pixabay is licensed under Creative Commons Zero v1.0 Universal

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.

A black arrow cuts diagonally downwards across the image towards the lower left, acting as an axis for a blue vertical wave labelled "electric field" and a red horizontal wave labelled "magnetic field". These waves are at right angle to each other. An arrow with heads at either end spans the length of the top of a vertical wave to the top of the next one.

This work by Piotr Fita is licensed under Creative Commons Zero v1.0 Universal

Wave-Particle Duality

Light is complicated as it can act as both a wave and a particle. Choosing how we want to talk about light - wave or particle - is only a matter of convenience.

An image of the gamma symbol — The gamma symbol which is used to represent a photon

Spectra

Even though light often looks white, it is made up of lots of different colours all added together.

When we talk about light we usually mean the light we can see with our eyes.

This is also called visible or optical light.

Light is one way energy can be transferred - moved from one place to another.

A bright sun at the top of image, slightly off-centre, shines down over tall, thin trees with green foliage. The sky is bright blue with some white clouds visible.

This work by Emmanuel Huybrechts is licensed under Creative Commons Attribution 4.0 International

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.

A white meshed grid against a black background. Three spheres of different size and mass sit on the grid, appearing to distort the grid beneath it. The largest sphere is yellow and causes the most distortion, with the next smallest being orange that causes less distortion. A red sphere is the smallest, with the mesh around it barely being distorted. — Artists impression visualising space-time being distorted by three spheres with different masses.

Relativity

Gravity is the force we are most familiar with in everyday life. It has been studied for longer than the other forces of nature. However, it is also the least well understood.

An image showing many galaxies within a cluster. Towards the centre, the light has curved, appearing to form the outline of a face and a mouth smiling whilst two bright galaxies look like the eyes. — A galaxy cluster appearing to have two eyes and a nose to form a smiley face. The eyes are actually very bright galaxies, and the lines are arcs caused by an effect called gravitational lensing.

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