What are the distances between the telescopes and Earth?
Hubble | JWST |
The Hubble Space Telescope orbits around the Earth at an altitude of ~570km | JWST will not actually orbit the Earth. Instead it will sit at the Earth-Sun L2 Lagrange point. This point is around 1.5 million kilometres further away from the Sun than the Earth is |
Space-based telescopes have a huge advantage over ground-based ones. By being above the atmosphere they don't have to peer through the shifting air to see into deep space, granting them a clearer view than most ground-based telescopes can achieve. They are also unaffected by the weather, which can be a big problem forastronomers.
However, being in space makes fixing things that go wrong considerably more difficult. Hubble famously had a small flaw in its mirror upon launch that required a mission into space to fix.
JWST will have no such rescue. At 1.5 million kilometres away, far further than any human has ever travelled, if something goes wrong it won't be possible to head into space and fix it.
It is being placed in such a remote place for several reasons. It keeps the telescope far from the reflected radiation of the Earth, one of many choices designed to keep this highly sensitive telescopecool. It will also be in a place where the gravity of the Sun and Earth work together, making it easier to keep the satellite in place.
How far back in time can JWST see?
The further away an object is, the further back in time we are looking. This is because of the time it takes light to travel from the object to us.
With JWST's larger mirror, it will be able to see almost the whole way back to the beginning of the Universe, around 13.7 billion years ago.
With its ability to view the Universe in longer wavelength infrared light, JWST will be capable of seeing some of the most distant galaxies in our Universe, certainly with more ease than than the visible/ultraviolet light view of Hubble.
This is because light from distant objects is stretched out by the expansion of our Universe - an effect known as redshift - pushing the light out of the visible range and into infrared.
Why has JWST been delayed so long?
Space projects often take longer than expected, but JWST has been more unlucky than most.
It was originally planned to be launched in 2007, but a major redesign, escalating costs and delays led to it being pushed back to around 2018. However, the testing period from 2016 onwards also suffered from long delays, and a further delay was imparted by the global pandemic of 2020.
The telescope finally launched on Christmas Day 2021 at 12.20pm GMT (7.20am EST). Over the next six months, the telescope performed a series of complex deployment operations, including the unfurling of its huge sunshield.
Watch the successful launch back via the NASA live stream below.
