Still, combining more than two telescopes is a must to improve the performance of the interferometer.Ī major step forward in this regard was AMBER, an instrument which saw first light in March 2004 and was capable of combining the light of three telescopes. Some help comes from the rotation of the Earth, which changes the orientation of the interferometer relative to the object being observed. This means that if you are observing two stars and one has a spot on its surface, you will never be able to say where it is,” Markus adds.
![eclipse book on tape eclipse book on tape](https://www.lbyr.com/wp-content/uploads/2019/05/9780316182935.jpg)
“With two telescopes you can only figure out symmetric structures. But like for VINCI, the fact that it could only combine two telescopes meant there were important limitations to what it could actually achieve. MIDI was ideal for observing the dusty environment around young and evolved stars, and around black holes at the centres of galaxies. “Just two telescopes because it's easier, and before you run, you first want to walk,” says Markus. The first instrument was VINCI, followed by MIDI in December 2002, both able to combine the light of two telescopes. There were empty bottles of champagne with the names of the instruments and the dates they were commissioned on them,” continues Markus. “Since the first fringes, we have tested a lot of VLTI instruments in that room. It's always great when you have done something new,” remembers Markus Schöller, a staff astronomer at ESO who uses the VLTI to study binary systems of stars orbiting each other “There were quite a lot of people that night, and we had a lot of fun afterwards. “I remember someone said that ‘I will never look at stars anymore as points’ as now we can see their shape, we can see they are disks,” concludes Philippe. And indeed, six months later the VLTI finally opened its eyes. How did Philippe and the rest of the team understand where the error in the length of the paths came from? “We suspected that the map of the Paranal grid, which defined where we had installed the siderostats, was not correct,” he says, “so we actually measured the alignment of the grid by looking at stars at night and determining the position of the North with a theodolite… just like sailors on boats with sextants centuries ago! We found the orientation of the grid to be a fraction of a degree off, meaning we were around 200 millimetres off with our instrumentation… an offset which made us wait two and a half nights to see the first fringes!”Īfter the first fringes with the siderostats, the team focused on getting ready for the fringes with the UTs. Since the VLTI observes infrared radiation, this means we have to be accurate down to a thousandth of a millimetre.” “This is very challenging, because stars move in the sky as the Earth rotates, so we have to constantly adjust the positioning of the instruments within a fraction of the wavelength of the collected light. “You have to make sure that at any time the lengths of the two paths are exactly the same, or you won’t be able to successfully combine the beams,” explains Philippe. It turned out that the problem was the length of the paths that the two light beams had to cover between the star and the instruments. And then at a certain point we got woken up because nice fringes had just popped up, it was amazing! This moment for me is present as if it was last night!”īut the fact that it took two and a half days for this process, much longer than the team expected, meant that something was off. There were two rooms in the VLTI building where we were working, and I remember people napping on couches or chairs in one of the two rooms.
![eclipse book on tape eclipse book on tape](http://3.bp.blogspot.com/_O5GTW8d1sx0/TEgBkjMqOuI/AAAAAAAABLE/vgyTN6ui0_M/w1200-h630-p-k-no-nu/Twilight-Eclipse.jpg)
“Most of us were working day and night, doing technical work during the day and observing at night, so we were very tired.
![eclipse book on tape eclipse book on tape](https://venturebeat.com/wp-content/uploads/2018/06/screen-shot-2018-06-04-at-2-23-42-pm.jpg)
“It took us two and a half nights to see the fringes with the siderostats and people were starting to be worried that something could be wrong,” says Philippe. “It was quick and may have looked easy, but it was the result of many, many years of preparatory activities.”Ī key preparation step took place a few months earlier: the observation of the first fringes with two small test telescopes called siderostats, which was by no means a walk in the park. “We could see the first fringes with the two UTs within the first few hours of the night,” remembers Philippe Gitton, an optical engineer at ESO.