Where is JWST in the sky

[E23 (Andras)]

Does anyone know how to find the James Webb Space Telescope in the sky.
It has to be near the meridian around midnight as well as near the ecliptic continuously when it gets to L2. But where can I find its accurate co-ordinates. JPL's 'Horizon System' website is no help. Since its tennis court size aluminised sunshield always faces towards the sun and earth it should be visible in any decent amateur telescope even at L2 1.5 million km away. Wonder what its magnitude should be.

[E23 (Andras)]

Should have done some work on this before I posted this query:
There is a website that can generate the ephemeris for JWST

https://unistellaroptics.com/ephemeris

Doesn't give a magnitude though.

[julianh72 (Julian)]

JWST was captured 4 days after launch on a 17" telescope, when it was just beyond the Moon's orbit (or about 1/3 of the way to L2).
https://www.virtualtelescope.eu/2021...s-29-dec-2021/

They estimated the Visual Magnitude to be about 14.7 - but at that time, the sun-shield was not fully deployed. The fore- and aft-pallets were extended full-length, but the kite-shaped sun-shield had not been spread out laterally.

Now that the sun-shield is fully deployed, the reflected sunlight should be at least 3 or 4 times more than its configuration at the time of the Day 4 capture (roughly 1 or 2 magnitudes brighter, say) - but this will be offset by the receding distance.

It is currently about twice as far away as at Day 4, leading to a 4-fold reduction in apparent brightness (about 1.5 magnitudes, say), which should be pretty much compensated for by the increased reflective area. When it reaches L2, it will be roughly 3 times as far away as at Day 4, which would be roughly a 10-fold reduction apparent brightness (about 2.5 magnitudes say), but again, largely compensated for by the bigger reflective area.

In summary - I would guess you'll be looking to capture a Magnitude 14 to 15 object (or thereabouts).

[julianh72 (Julian)]

Originally Posted by E23

It has to be near the meridian around midnight as well as near the ecliptic continuously when it gets to L2.

Webb will orbit around L2, in a "halo orbit" similar in size to the Moon's orbit around the Earth, taking about 6 months to complete.
https://webb.nasa.gov/content/about/orbit.html

Since L2 is about 4 times as far from Earth as the Moon, JWST's apparent motion from Earth should be something like an ellipse around a point directedly overhead at midnight, but about 10 to 15 degrees away.

By orbiting around L2, but never actually getting close to the Sun-Earth straight line, it will always be in full sunlight, and will always be generating full solar power. (This also minimises the thermal distortion effects that would arise if it was to pass in and out of the Earth's shadow.) It also means that the comms link to Earth is always pointing well away from the Sun - which would be problematic for interference etc.

It's all very clever - when people say of something mundane that "it ain't rocket science" - THIS is the sort of complexity and ingenuity they're talking about!

[E23 (Andras)]

Thanks Julian. I tend to agree with your logic on the estimate of its visual magnitude at L2. Which means it will be easy to image it with my C14 and CCD camera which can easily reach 19V.

It appears from the website you quoted that its orbit around L2 is the size of the moon's orbit so I figure that the 6 month excursion in the sky will by a whopping 30 degrees across centered on the actual L2 co-ordinates in the sky.

I do a lot of astrometry for the MPC so I can hardly wait for the sky to clear in Sydney to take some images. The JWST is now about 500,000km from Earth.

[PaulSthcoast (Paul)]

Video shows the JWST in Orion.

https://youtu.be/qfKSeGTf0jk

Paul.

[BlakPhoenix (Rohan)]

Currently the JWST is near the Rosette nebula, but it will continue to change as we orbit the sun. Since the L2 point is always away from the sun, so the JWST will always be in our night sky and as such in different constellations. It's not overly hard to capture, but will become more difficult as it continues to move father from us. I managed to do so on 3 occasions with only a RedCat 51.



The most precise way to find it is with the JPL Horizons App: https://ssd.jpl.nasa.gov/horizons/app.html



I put together a little video detailing how to photograph it here if you're interested in more info: https://youtu.be/O5NC99suIhA