Someone posted a question if you can see the JWST with a telescope on Earth and I thought pffft of course not, could you see a bus parked on the moon? And now move that bus four times as far away as the moon.

And then people posted pictures of the JWST taken in the backyards of amateurs with tracking equipment.

It is just a dot, yes, but it is actually a dot slightly bigger and brighter than the stars around it.

That said, you can't see it with binoculars as you can with e.g. the ISS.

‌‌#JWST #JamesWebb #JamesWebbSpaceTelescope

Some people, journalists and JWST fans alike, are claiming that it's in the Earth's shadow.

No. The JWST has solar panels. It's on a very wide orbit around L2 so that the moon will never come between it and the astronomers who want to communicate with it, and so that Earth will never come between the sun and the solar panels.

The heat shield needs to shield against the full power of the sun all on its own.

Many of the infographics out there are very symbolic, like a subway map; They're not to scale and everything is circles. Webb's orbit around L2 is often shown as similar or smaller than the moon's orbit around Earth. Here is an accurate illustration.



Image: NASA/STScl

@clacke I still don’t understand how an object can orbit “around” L2 (which is a point in space, right?). Do you happen to have a link to a good explainer because I haven’t been able to find one.

@torgo I haven't seen a real explanation, but here's how I imagine it works out.

What keeps us in orbit around L2 is the composant of Earth's gravity in the plane of our L2 orbit and what allows us to go with the same orbital period around the sun as Earth, even though we're farther away and should have a longer period, is the composant perpendicular to our L2 orbit, pointing toward the Sun.

If you look at just Earth and a satellite, and you have the satellite go a million miles toward you and then half a million miles up and you kick it hard to the right, it would spiral down to Earth, right? It would be on a kind of orbit around a line going down to earth, and that orbit would move toward Earth, probably pass it and oscillate like a pendulum.

But now we add the sun. So Earth orbits the sun and our orbit also orbits the sun and the way it plays out at L2 is that actually we're heading in the tangent just fast enough that our orbit never falls toward Earth.

@torgo

It's screwy for sure. I only figured this out just now (if I did indeed figure it out, don't take my word for it, there is no math here, only geometrical intuition).

And the orbital shape is really weird. As the L2 orbit also needs to go around the sun it will be a bit bent around the sun, so it looks a bit saddle-shaped. It's not a stable orbit, it's merely a "helpful" orbit. They will do corrective burns once every 21 days for ten years until the fuel runs out.

They actually put a refueling hatch on there, with handles for a craft to hold onto, but currently no such mission is in the pipeline.

@torgo