Take delight in the details
THE big astronomy news this week was the release of the first images from NASA’s James Webb Space Telescope – the instrument that is about four times as far away from us as the moon and has the famous gold-plated segmented mirror.
The images show the universe in stunning detail, as we look back to its younger days across a huge chasm of space and time and peer at spectacular objects within our own galaxy.
It’s a quite remarkable achievement to have the JWST working so perfectly – although that was, of course, always the aim!
One of the great difficulties in establishing a space observatory of this size was for the mirror to assemble itself correctly. The 18 hexagonal segments needed to be placed and aligned perfectly, so that working together, they operate like one single mirror about 6.5m across – and all that had to happen out there in space.
The significance of the mirror of a reflecting telescope is that it gathers and focuses the light falling on to it, forming an image of a distant object.
That image can be captured by a CCD (or, in the old days, using photographic film or plates) and analysed using various techniques.
In telescopes for visual use, the image is viewed through a
small lens system known as an eyepiece, although that certainly doesn’t happen with the JWST!
The larger the mirror, the more light it gathers, allowing fainter objects to be detected. A larger mirror also means a sharper image – provided, of course, that the mirror is optically perfect.
The mirror of the JWST is as perfect as one could imagine, which is all the more special given that it is made up of 18 pieces.
NASA had earlier released some test images from the JWST, which already showed that the optics were in good alignment.
The final result – the first science images, which we now see – proves that to be the case. They are breathtaking.
The stunning picture officially released on Monday by US President Joe Biden shows intricate detail in a tiny patch of sky in the direction of the constellation of Volans, the Flying Fish.
Look up to the sky tonight about 7pm and face towards the Southern Cross, which is high in the sky a little to the right of due south, and look down to about halfway to the horizon. Above and to the left of the very bright star Canopus is the location of that rather dim constellation.
In that picture, almost all of the points of light are distant galaxies, and they include some of the farthest ever seen. The telescope’s ability to do this is not only because of its great light-gathering power. It is also because it concentrates on observing mainly infra-red light, rather than the visible light to which our eyes are sensitive.
Indeed, this is the “deepest’’ infra-red picture of the sky ever taken, in the sense that it penetrates right out to the faintest objects ever imaged at these wavelengths.
The very bright points are foreground stars in our own galaxy, but the “spikes’’ are not real. They are called diffraction spikes, caused by the way light negotiates edges, gaps and obstructions in the optics, which are dictated by the way the telescope is constructed.
The cluster of galaxies in the centre of the image is “only’’ about 4600 million light years away. Its gravitational field has bent and distorted the light from those galaxies in an effect called gravitational lensing, allowing us to see detail in them, and giving information about the structure of galaxies in the early universe.
Early on Tuesday morning our time, four more images were released. The picture of the “Southern Ring’’ nebula shows material that has been ejected from a dying star. The stunning detail shows the results of the individual outbursts, like layers of an onion expanding into the surrounding space.
These images show what we had all hoped for. I feel confident the JWST will greatly expand our knowledge of the universe – from topics such as star formation in our galaxy and others, to the detailed history of the early universe.