In November’s episode of The Sky at Night, Paul Eccleston looked forward to the long awaited launch of the James Webb Space Telescope
This Christmas, astronomers around the world will be eagerly awaiting more than their presents, as the largest space telescope ever built will be blasted into orbit. The James Webb Space Telescope (often known as the JWST or just Webb) is due to launch this December on an Ariane 5 rocket from French Guiana to the L Lagrange point, where the gravitational pull of Earth and the Sun adds together to pull the spacecraft around the Sun in 365 days, keeping pace with Earth. At this stable location, 1.5 million kilometres from Earth, the spacecraft will be able to study the Universe in unprecedented detail.
Conceived in 1989 as the successor to the Hubble Space Telescope (then approaching launch), JWST will take over as the world’s flagship space observatory. Its 6.5m diameter primary mirror provides more than seven times the collecting area (and therefore sensitivity) of Hubble. Key scientific aims for the mission include searching for light from the first stars and galaxies (13.2 billion lightyears away), looking at how galaxies form, studying the life cycles of stars, and examining how planetary systems are born.
To answer these fundamental questions about our Universe, Webb will reach out into the infrared (IR) wavelengths on the electromagnetic spectrum as well as visible light. The light from the very earliest galaxies has been red-shifted so far that these stars are best observed in infrared wavelengths.
Additionally, this light passes through dust and gas clouds that surround regions where stars and planets are born, which gives us a unique insight into the factors that drive the diversity of planetary systems we now see. To see the infrared radiation given off by these distant or cool objects, the JWST must itself be cryogenically cooled. To keep the telescope and instruments below –228°C the telescope hides from the Sun and Earth behind a sunshield made of five ultra-thin layers of aluminised foils, each one the size of a tennis court but less than 1/20th mm thick.
The sheer scale of the telescope and sunshield prevents it being launched fully deployed, so within two weeks after launch a series of mechanisms will unfold it to make the complete spacecraft. With such a complex machine, and no chance of repair once launched, there has been a painstaking and timeconsuming process of repeatedly checking everything to make sure all goes as planned. By necessity, this has led to a very long gestation period for the mission in order to minimise the risk of anything going wrong. JWST is an enormous international effort, led by NASA with contributions from Canada and Europe. The European contribution includes the launch, the Near-InfraRed Spectrometer (NIRSpec) and the Mid-InfraRed Instrument (MIRI). I led the team responsible for MIRI, which captures the longest wavelength of light (5-28 microns). It was built by a consortium of 12 European countries (led from UK ATC in Edinburgh) and the US, with the assembly and calibration conducted at RAL Space in Oxfordshire.
Thousands of us around the world who have collaborated over the past 20 years await the final part of JWST’s journey from drawing board into fully operational telescope. The results will surely be fascinating as we open a new window on our Universe.
Paul Eccleston is Chief Engineer at STFC’s RAL Space facility. He led the team calibrating the MIRI instrument for the JWST
Looking back: The Sky at Night
9 December 1966
On 9 December 1966 episode of the Sky at Night, Patrick Moore looked back at an unexpectedly spectacular astronomical event that had happened the previous month. The 18 November was the peak of the Leonid meteor shower, created by Earth passing through the trail of gravel-sized debris left behind in the wake of Comet 55P/Tempel-Tuttle. Most of the time, the meteor shower is one of the weaker showings of the year, with a zenithal hourly rate (ZHR) of just 10-15 meteors, but once every 33 or so years, it is a completely different story as the parent comet returns to the inner Solar System and refreshes the debris stream.
In 1966, the comet had returned, and hopes were high about an impressive showing, at least for North America where it would be night-time when Earth passed through the densest part of the stream. However, the shower was far grander than anyone’s expectations, with reports of multiple meteors a minute. The peak rate was recorded at 4:54am at the Kitt Peak National Observatory in Arizona at an astonishing 40 meteors per second (around 144,000 per hour).
The next potential outburst should have been due in the early 2030s, but unfortunately the comet will make a close approach to Jupiter in 2028, throwing off its orbit enough that a repeat showing is unlikely.
It’s been quite a year for astronomy and spaceflight, and once again Maggie, Chris and the rest of The Sky at Night team have been at the forefront, bringing the latest space news and stargazing advice to viewers over the past 12 months. This episode the team look back at the year that was, and pick some of their highlights from The Sky at Night in 2021.
BBC Four, 12 December, 10pm (first repeat BBC Four, 16 December, 7:30pm)
Check www.bbc.co.uk/skyatnight for more up-to-date information
