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Tracking the JWST

The NRT's design, operations model and science case are closely linked to the Liverpool Telescope (LT). The Liverpool Telescope monitors all kinds of objects in space ranging from gamma-ray bursts to exoplanet solar systems, blazars, supernovae and novae, to name but a few! The LT also tracks human-made satellites such as Gaia, which launched in 2013 and is still gathering data. One of the most exciting telescope-related events this year, the launch of the James Webb Space Telescope (JWST), happened on 25th December 2021 and the LT was there to track it as it travelled through space.

Animation of a cartoon Liverpool Telescope waiting for the JSWT to launch
The Liverpool Telescope awaits the launch of JWST.

The JWST is a revolutionary telescope and astronomers and engineers across the world have waited patiently for its completion and launch for many years. Located outside Earth's atmosphere, space satellites like Hubble and JWST have an unencumbered view of our Universe. Hubble has provided astronomers with incredible deep images of distant galaxies, but JWST will have a 6.5 metre mirror, capable of catching more photons than Hubble's 2.4 metre mirror, and therefore probing even further into the depths of our Universe. The JWST will look back over 13.5 billion years at our Universe in optical and infrared wavelengths and explore the formation of the first stars and galaxies. As JWST is designed to allow for measurements at infrared wavelengths, it is perfectly primed to see through the dust enshrouding many objects in the Universe such as stars and planetary systems. JWST will also explore distant exoplanet systems and objects within our own Solar System.


As the JWST is a near-Earth object, it needs to be observed using non-sidereal tracking; the route it takes across the sky is different to that of distant objects. In order to carry out non-sidereal tracking, the LT requires an ephemeris; information from NASA about the trajectory of the JWST. This ephemeris information is entered into the phase 2 graphic user interface (GUI) and the observation group is then automatically scheduled by the LT software.


Animation showing the JWST
Gif of the JWST travelling across the sky (created by Jon Marchant).

The above gif is made up of four LT IO:O images of the satellite as it travelled at speeds of approximately 1.5 miles per second through the solar system towards its destination of the L2 Lagrange point. The JWST telescope is visible just above the centre of the frame and appears as a bright point-source. The other sources in the frame are distant objects in the Milky Way, they appear as elongated sources due to the non-sidereal movement of JWST and the 10 second exposure times.


The LT will observe the JWST a second time on its month-long journey in the coming days. We expect to see a change in the brightness of the satellite as now it has successfully deployed its sunshield.