Orwell Astronomical Society (Ipswich)
James Webb Space Telescope (JWST), 21 January - 16 December 2022
The JWST was launched on Christmas Day 2021 and travelled towards the Lagrangian point L2 some 1.6 million km from Earth.
On 21 January 2022, I imaged the JWST at a distance of some 1.35 million km. The ephemeris from Project Pluto showed the object drifting at 1.7 arcsec per minute relative to the stars, limiting exposures to approximately 1 minute duration in order to minimise star trailing. The JWST was marginally visible in individual frames of 1 minute duration, so I aggregated groups of ten consecutive frames and assembled the groups to form the movie below.
The video shows the brightness of the JWST varying significantly, an effect which has been noted elsewhere, e.g. https://britastro.org/node/26452. At the very end of the video clip there is a flare.
The short break and jump in all videos on this page is caused by the telescope performing a meridian flip.
The JWST entered orbit around L2 on 24 January 2022. On 22 February 2022, I was able to image the object at a distance of approximately 1.5 million km at around magnitude 16. The video below comprises two distinct segments. The first shows the JWST moving among the stars; the second is centred on the instrument, showing the stars moving. The still image shows the track of the JWST among the stars.
The JWST at L2 is the most distant man-made object that I have observed!
After entering orbit around L2, on 15 March 2022, the JWST achieved its highest declination of +19°, and on subsequent days culminated as seen from the UK at an altitude of +54°. After this, it began travelling southbound towards its lowest declination of -38° in early July, when it will be invisible from the UK. It will then climb northwards again towards a maximum altitude of about +66° in mid-October.
On the night of 19-20 March 2022, I imaged the JWST again. The Moon, just after full (phase 96% waning), was only some 45° away, making the sky bright. As the JWST was close to its highest declination, its apparent motion was essentially horizontal, dipping slightly towards the end. The object was of magnitude approximately 16-17, but this varied, and there were some brighter glints as it moved.
To produce a file of manageable size, I created the video in PAL TV format, giving it a slightly strange appearance.
After entering orbit around L2, the JWST began a six-month commissioning activity. One of the early commissioning tasks was to spend several weeks imaging star HD84406 (Hipparcos 48034, Tycho 4139-971-1) to enable alignment of the 18 primary mirrors and perform initial focussing. (The star is located some 258 ly distant in Ursa Major in a relatively sparsely populated area of the sky, thus easily found. By 18 February 2022, Phase 1 of the procedure to align the 18 segments of the primary mirror was complete.) The NIRCam (near-infra red camera) instrument on JWST used to image HD84406 has a pair of apertures each with a Field of View (FoV) of 2.2 x 2.2 arcminutes. On 22 March 2022, I used a 200 mm Celestron Edge HD and SBIG 8300 camera, with a much larger FoV, to image the star field around HD84406, shown below.
After completion of initial focussing, another star, 2MASS J17554042+6551277 (also catalogued as Tycho 4212-1079-1), was used for final focussing. The star is a magnitude 11 object in Draco. My image of the star, taken on 26 March 2022, is below. There are several faint galaxies in the background field - two are marked.
Later, in the evening of 26 March, I took the opportunity to image the JWST itself. In recent weeks, its orientation relative to the Earth has been changing, making it slightly brighter. It is now at around magnitude 15, easily captured in a single 60 second exposure.
On the night of 01 April 2022, I took the opportunity to image the JWST again. It was around magnitude 14.7, similar to when I had last observed it, and again easily captured in a 60 second exposure.
Below is a video captured from a 4+ hour sequence of images, showing the JWST moving amongst the stars. It is initially easily visible, however, in a period of some 10 minutes duration around 22:00 UT, it all but vanishes from view! In individual frames at this time it measured close to magnitude 18, making it hard to identify. The video below ends when my telescope performed a meridian flip. A 2 hour sequence (not shown) following the flip revealed that the JWST continued to appear very faint.
On 20 October 2022, the JWST was at declination +29° 35', heading towards its highest declination of 29° 57' on 25 October, before heading south again. I recorded the JWST moving through the stars of Aries. I used a Celestron 200 mm Edge HG with LPF and SBIG8300 camera with 2x2 binning. With this equipment, the JWST was not visible in individual 1-minute exposures. However, I was able to reveal it by aligning the images on the predicted position of the craft and stacking them in groups of ten.
By 20 December 2022, the JWST was a working observatory, and I decided to make another video of it against the background star field. My usual checking of the first few frames of the video to confirm that everything in the image-processing train had worked properly proved unsettling as I could not see the JWST and it was only by checking the final frames that I realised that the craft was where it was supposed to be, but had been very, very faint. In fact, the brightness of the JWST varied considerably and, in order to make it visible throughout the entire sequence, I constructed subframes for the video by stacking 10 consecutive one minute exposures centred on the craft.
In the video below, the field of view is split: the LHS pane tracks the stars and the RHS the JWST. Initially the craft is all but invisible but, about halfway through the video, there is a glint (magnitude ~15) from part of the structure before the magnitude settles down to around 17. In the LHS pane, the JWST is invisible for the early part of the sequence; in the RHS, thanks to the stacking of 10 consecutive frames, it is visible throughout.
At a distance of 1.7 million km, the JWST is the furthest man-made object that I have observed.
Below is a stack of frames from the video: on the LHS tracking the stars and on the RHS tracking the JWST.
Nigel Evans