The James Webb telescope is a lot larger than Hubble. The HST has a primary mirror with a diameter of 2.4 metres. The mirror on the JWST is a multi segment 6.5 metre design. This means that is has a light gathering power around one thousand times the power of the telescope I have in my observatory. This mirror is designed to work in the visible and near infra-red wavelengths. The James Webb telescope is intended to work more in the infra-red, hence the pretty gold mirrors, which reflects infra-red well. The mirror segments themselves are made of beryllium coated in a thin layer of gold. My telescope on the other hand is made of rather more mundane plate glass covered with a thin layer of aluminium. Unlike domestic mirrors, the reflecting surface of a telescope mirror is always on the front, not the back.
Although we are familiar with the visible light images from Hubble, imaging in the infra-red is far more interesting for science. Infra-red light allows us to see through the dust and murk in outer space which sometimes hides scientific targets. Most land based telescopes have to work in the visible and near infra-red spectrum because the water vapour in the Earth’s atmosphere tends to absorb a lot of the infra-red light.
In another departure from Hubble, the James Webb telescope will not be parked in the conventional low-earth orbit. To shield the detectors from infra-red light from the Sun, the JWST will be parked in an orbit around the L2 Lagrangian point on the other side of the Earth from the Sun. Thus the Earth acts as a giant sun screen. This makes telescope operation much easier, but does have the downside that no servicing missions are possible with current technology. The Lagrangian points are regions in space where the gravitational attraction of large orbiting bodies (i.e. the Sun and the Earth) is cancelled out - making quite a nice hideout for a spaceship.
This image shows us part of the mirror assembly at the testing facility. Before committing the telescope to launch, each part of the assembly must be tested by cryogenically cooling and then heating the telescope to test how it will respond to the extreme conditions found in space.
I enjoyed this shot of the engineers working on the mirror segments. IT is quite funny that you see a mundane object like a litter bin (bottom left) next to all the high technology.
Image credit: (NASA/Emmett Given)
Centaurus A, known to us Astronomers as NGC 5128 is 11 million light years away in the constellation of Centaurus is not visible to us Astrophotographers in the north, so it is a delight to see a "foreign" object for a change. This galaxy is extremely active with lots of exciting star forming regions. However, its appeal comes from the large amount of dark dust lanes that cross our view of the galaxy and hide some of the millions of stars in the galaxy.
Hubble has really gone to town on this one with the Wide Field Camera 3 which was installed a few years ago in the last shuttle servicing mission. Seven different filters were used to make up this image. Data from different wavelengths, from the violet all the way through to the infrared have been combined to produce this image. This is the most detailed image ever taken of this region.
The bright pink/purple regions are intense star forming regions similar to some of the active nebulae we image in our own galaxy with our hydrogen alpha filters. The orange/yellow areas show older stars, some of which doubtless orbit around the super-massive black hole which resides at the centre of this galaxy.
The second image shows a crop of the full sized version.
Image credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration. Acknowledgment: R. O’Connell (University of Virginia) and the WFC3 Scientific Oversight Committee