How do telescopes work?
Introduction
Owing to the fact that the James Webb telescope is set to launch in just under two weeks, I thought it would make sense to go through how telescopes actually work.
“The telescope… is a conduit to the cosmos.”
- Neil deGrasse Tyson
Now before we go over how telescopes work, we need to understand how we see objects.
We see objects due to the reflection of light. Light is emitted from objects like the Sun as well as artificial light sources like lamps. This light then bounces off of each object before it enters our eyes. If a certain object is blue in colour, that object will absorb every colour except the colour blue, which it reflects. Light is actually a spectrum of different colours.
Various cells in our eyes then send signals to the Brain which interprets what we see in a fraction of a milisecond.
To put it bluntly, telescopes work exactly like we do, they capture light reflected from other objects… but why can we see further? This is thanks to mirrors inside the chassis of the telescope. There are also different types of telescope that “exploit” different properties of light to enlarge images we see.
The picture above is a very simple representation of a refracting telescope. These telescopes make use of “refraction”, the process by which light changes direction when it enters a medium. of different density. Refractive telescopes contain two main lenses, the objective lens and the eyepiece. Every lens has what is known as a focal length. This quantity is the distance from the lens to the focus, which is simply the point at which light rays converge or diverge. The eyepiece is kept slightly beyond the focal length.
As light enters the telescope, the objective lens causes it to refract. They converge at the focus. This light then once again goes through the eyepiece and refracts into the eyes. This forms a large virtual image, an image in which the rays of light do not converge.
However, refractive telescopes have their limitations. Firstly, refractive telescopes suffer from chromatic aberration, a situation in which the colours of light cannot focus at the same point, this causes the image to get blurred. Furthermore, as the actual telescope becomes larger, the lenses tend to get distorted which can produce distorted images.
There is however a solution, use a reflecting telescope!
Reflecting telescopes use multiple mirrors that instead use the process of reflection. Essentially, the primary mirror or the objective lens is parabolic which allows it to have a long focal length. Light initially reflects off of the primary mirror before it hits a secondary mirror. It then passes into the eyepiece which allows us to view the object. There are different types of reflecting telescopes like a Newtonian telescope and a Cassegrain telescope.
Cassegrain telescopes are much smaller than Newtonian telescopes because light travels around the telescope three times more than it does in a Newtonian telescope which allows it to be be smaller without compromising on image quality.
NASA’s Hubble Space and James Webb Telescopes are reflecting telescopes. These telescopes are said to be better than refractive telescopes as they overcome their shortcomings.
Thanks for reading, I hope you guys enjoyed!
