If you want precise positional information about a distant object, surely you'd need the individual sensors to be as far apart as possible. So why are these fibre optic heads placed so close together that they have to be careful not to make them collide with each other when adjusting their aiming line?
Lawrence Berkeley National Laboratory boffins are getting ready to point thousands of optical fibres at the night sky, starting with a 10-robot system proof-of-concept. The ProtoDESI the boffins are wiring up will use robots to aim optical fibres at distant galaxies, a light-gathering trick the DESI (Dark Energy Spectroscopic …
Tuesday 14th June 2016 11:05 GMT Flocke Kroes
How it works
The instrument starts with a big mirror, like a normal telescope, but instead of putting a CCD in the focal plane, there is a large number of ends of fibre optic cable. Point the big mirror at patch of sky, and move it to counter the rotation of the earth, then each optical fibre gets the light from a different galaxy. Presumably the other ends of the fibres are lined up pointing at a diffraction grating to split the light into colours, and the result goes to a CCD so you get a complete spectrum of a bunch of galaxies in the same patch of sky in one go. Every time you pick a different patch of sky all the fibres have to be moved, and that appears to be the tricky bit.
Tuesday 14th June 2016 13:54 GMT Boothy
Re: How it works
The Sloan Digital Sky Survey (SDSS) basically did the same process a few years back (the fibre bit), but without the robots, so was a very manual process. Basically drilling holes in plates for the fibres, that lined up with the galaxy positions in a specific area of the sky.
I remember watching a documentary about it a few years ago, took them days to set up a single plate.
This is basically automating the process, to ramp up the numbers (massively).
A couple of pics and some further links/reading here.
Tuesday 14th June 2016 14:21 GMT Boothy
@ frank ly
Quote : "If you want precise positional information about a distant object, surely you'd need the individual sensors to be as far apart as possible...".
The galaxies are too far away to use trigonometry to measure distance. We can use that for neighbouring stars, but once you get past a certain distance, it becomes very inaccurate.
So this about grabbing the spectrum of the galaxies, which gives us the red-shift, which tells us how far away the galaxy is far more accurately at these distances than trigonometry would.
We've done this already on a smaller scale, so this is about doing it on mass.
Quote: "So why are these fibre optic heads placed so close together that they have to be careful not to make them collide with each other when adjusting their aiming line?"
Don't think aiming, think more filter. It's one fibre per galaxy.
Imagine a disk (i.e. a disk of aluminium about a meter across), now drill holes in that disk that precisely match with the relative positions of galaxies in a specific area of the sky. Stick this plate at the end of a telescope (where the camera normally is), and point it at that section of the sky, so that the light from each galaxy lines up exactly with the holes on your drilled plate.
Now direct via fibre optics the light from each hole to a sensor, and you can measure the spectrum of each galaxy, one fibre being the light from one galaxy.
This was basically the Sloan Digital Sky Survey, check out wikipedia etc for some pics.
This new work is to automate the process, so rather than drilling metal plates, and fitting the fibres, a plate for each section of sky, you just move the fibres around via the 'robots'.
Tuesday 14th June 2016 07:37 GMT Michael H.F. Wilkinson
Ten million galaxies is nice, but it is all about spectra
The Sloan Digital Sky Survey release 12 has far more objects: 208,478,448 galaxies to be precise. It only contains spectra for 2,401,952 galaxies and 477,161 quasars, so DESI becomes particularly interesting because it captures spectra of so many objects.
Pointing an optical fibre directly at the sky is of course pointless, as the aperture is pathetically small. The trick is to get a big mirror (4 m in this case), which gathers a lot of photons, and use fibre optics to guide the light to (multiple) spectroscopes. The more usual trick is to use a slit, which captures spectra from a little stripe across the image plane. By using carefully placed fibre optics, the project (as I read it) wants to tap into more of the optical plane, to record spectra of far more objects simultaneously. The robots pick out the right bits of the image from which to obtain spectra. Sounds very interesting
Tuesday 14th June 2016 07:43 GMT Christopher Lane
Tuesday 14th June 2016 11:56 GMT Anonymous Coward
Tuesday 14th June 2016 12:40 GMT ravenviz
Tuesday 14th June 2016 13:04 GMT Graham Cunningham
wonders will never cease!
There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable.
There is another theory which states that this has already happened. - DNA
Tuesday 14th June 2016 23:47 GMT VeganVegan
Thursday 16th June 2016 00:06 GMT Mark Exclamation