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.
Light and Telescopes
One of the first people to study light was Ibn al-Haytham (known as Alhazen). He was a Muslim, living in Egypt in the early 11th Century. Alhazen is first person we know of who used the scientific method. He wanted to know why our eyes could see things.
Hans Lipperhey (also spelt Lippershey) was the first person to write down a design for a telescope. He made spectacles for a living, and in 1608 he applied for a patent for his new tool. He said it was "for seeing things far away as if they were nearby". Hans did not get the patent because other people were making similar tools. But, Hans was paid for his design. The first telescopes, known as Dutch Telescopes, contained both a convex and a concave lens.