Eli5 Space telescopes image capturing process


How do NASA scientists know where to point the camera from the James Web Telescope. If the camera is pointing one direction , what are we missing by not focusing on other areas?
Help me understand , because in my simple mind there’s space all around us & taking a picture usually only captures what in front of you .

In: 1

Things in space still exist in some specific location, like specific stars. You’d face the thing you want to take an image of. You work that out by taking the position you see the object from earth, the position of the sun or some other reference points, and do some 3D trigonometry to work out where to face.

As for what you miss, it is like anything. If you take a photo of what is in front of you, you miss everything that isn’t in the direction you look.

What you miss totally depends on what you are not facing. There is “stuff” in all directions.

> how do NASA scientists know where to point the camera

Thousands upon thousands of scientists submit proposals to the Space Telescope Science Institute (STScI) asking them to point JWST at a target the scientist is interested in. In this proposal they tell them where they want to point it, how long, and what science they hope to gain from it. A group of scientists at STScI then review these proposals, accept a fraction of them, and schedule the observation. The director of JWST also has a small amount of alotted time every month or so where they can point it wherever they want, usually going to some mystery part of the sky just to see if anything new is there.

>What are we missing by not focusing on other areas?

Probably something, even Hubble has only seen like 1% of the whole sky. It’s up to the scientists submitting proposals and the director to maximize what we can get from the limited lifetime of JWST. There are also lots of other telescopes on earth and in space that provide tons of other pictures as well. Many specialize in seeing large swaths of the sky for people to see if there is anything interesting out there

well we can point the telescope in different directions and move it around, so we can image one thing and then move to another. How we decide what to image depends in part on the telescope and what it was made for. For JWST and other NASA telescopes, an observation proposal system is used, where scientists propose things that should be observed, and a group of scientists review the proposals to decide which ones to do. They will also do some observations for people who have been guaranteed an observation in return for work they did in the development of the telescope.

You can see the approved proposals here:


They generally choose to look at targets that we have looked at before with other instruments, but with a plan to use the JWST to get a better look at the target. Sometimes it will be looking at a specific planet, and using the instruments of the telescope to analyse the atmosphere. Other times it might be doing something like imaging general galaxies and looking at specific stars in the galaxy to calibrate our methods of measuring distances, like in this proposal:


With JWST, the heat shield needs to be kept facing the sun, but it can still rotate 360 degrees while keeping the heat shield facing the sun. This means that while it can’t be pointed anywhere at anytime, it can be pointed to most places, and by waiting for its orbit to take it somewhere else we will be able to then see more places.