There’s actually another good reason to use infrared light for JWST: It’s very difficult to get an unobstructed view of distant objects thanks to the gas and dust that is the debris of old stars. They can scatter visible light more easily than infrared wavelengths. Essentially, infrared sensors can see through these clouds better than visible light telescopes.
Since JWST is observing in the infrared spectrum, scientists will need everything around the telescope to be as dark as possible. That means the telescope itself needs to be extremely cold to avoid emitting its own infrared radiation. This is one reason why it has a sunshade. It will block sunlight from the main appliances so they can stay cold. It will also help remove excess light so the telescope can pick up relatively dim light from alien planets as they orbit their much brighter host stars. (Otherwise, it would be like trying to see in the dark while someone shines a flashlight in your face.)
How does JWST look back in time?
Light is a very fast traveling wave. In just one second, light can go around the circumference of the Earth more than seven times.
When observing celestial bodies, we must take into account the time it takes for light to travel from the object to the telescope or to our eyes. For example, light from the nearby Alpha Centauri star system takes 4.37 years to reach Earth. So if you see it in the sky, you’re looking 4.37 years in the past.
(Actually, everything you see is in the past. You see the moon about 1.3 seconds in the past. When detected closest to Earth, Mars was three minutes ago.)
The idea is for JWST to be able to see past more than 13 billion years, into the evolutionary time of the universe when the first stars were formed. That’s awesome, if you think about it.
What is Lagrange Score?
The Hubble Space Telescope is at low earth orbit, which is great because astronauts can use it as needed. But JWST will be much further away, at the Lagrange point L2. But what the hell is the Lagrange score?
Consider Hubble orbiting the Earth. For any object moving in a circle, there must be a centripetal force, or a force pulling the object toward the center of the circle. If you swing a ball on a rope around your head, the force pulling it toward the center is the tension in the rope. For Hubble, this centripetal force is gravity due to its interaction with the Earth.
As an object moves away from the Earth, the strength of this gravitational force gradually decreases. So, if the telescope moves to a higher orbit (larger circle radius), the centripetal force will decrease. To stay in a circular orbit, it would take Hubble longer to orbit. (We would say it has a lower angular velocity.)
