Tweet Your Way to the VLT, day 4: Thor’s Helmet (English version)

I don’t know whether the feeling ever goes away, but for my part at least, sleeping seems like a waste of time at Paranal. So I meet up again with Mathieu at 4.45am in the residence’s hall, after a night’s sleep whose length in hours could be counted on half the fingers of a hand…

We still need to make the observation that is the objective and purpose of my visit – that of the nebula NGC 2359, appropriately nicknamed Thor’s Helmet.

So here it is, as it’s been known up until now…

Crédit image: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin

We meet up once again with Henri Boffin in the control room of UT1, and immediately begin the preliminary observations. The first thing to do is obviously to point the telescope at the nebula using a guide star. Each time the telescope moves, a loudspeaker announces “there is no cause for alarm,” followed by “but there probably will be!” when it’s in position. In fact, all the sounds produced by the software come from films or cartoons, and even if the joke seems surprising at first in such a serious environment, you can get used to it very easily.

We plan to take several monochromatic images of the nebula, using filters that isolate different components: I remember specifically the terms ionised hydrogen and oxygen being mentioned, for example. Henri also tries different exposure times, but the images that come from 30 second exposures are astonishing. These telescopes really are impressive. We make no exposures longer than three minutes, to avoid horribly over-exposing the brightest stars in the nebula.

We take several different photos using the same settings, but moving the telescope slightly, which will allow us to hide the black line that runs through the image. This is caused by the fact that the images are produced by two CCD detectors that do not touch each other.

If the black and white images made by the telescope are perfect for science, those destined for the public, in ‘true’ colour, need some post-production. Aside from removing the black line, each monochromatic photo needs to have a colour assigned to it before they are combined together. The colour assigned to a filter obviously corresponds to the colour that the component of the nebula emits, for example, green for ionised oxygen. The combined exposure time for all the exposures that are assembled for the image is around 3 hours in total.

Henri takes the time to show me in the software the commands that let him start and stop observations, change filters, exposure times… and look at the image that has just been taken. We also talk about the wind, which at 10 metres per second could become a cause for concern. Above 12 metres per second, the telescope has to be oriented at 90º to the wind, and if that happened we would have to stop observing, as we would not be able to point the telescope towards ‘our’ nebula. Above 18 metres per second, the telescope dome has to be closed.

We’re on live from 6am to take part in the “A Day in the Life of ESO” broadcast, presented by Dr Joe Liske, an ESO astronomer. Organised to mark the 50th anniversary of ESO, this broadcast will last six hours, and the live sessions from Paranal will be the beginning and end. Obviously I suggest you take the time to watch it all – all the segments are available on ESO’s site!

The images that appear on the screens are of course monochromatic, but they are superb to my eyes. Henri Boffin is delighted with the result, and since, unlike me, it’s far from his first observation, the final image will surely be a great success.

The live show goes well, and as soon as it’s over, I go up onto the platform to watch the closing of the telescopes. The Closing sequence takes 25 minutes and has to be finished before sunrise, at around 7.10am.

Sunrise is superb, the light is quite simply extraordinary. I realise that I have still only barely mentioned the four auxiliary telescopes, which, uniquely, can be moved around the platform thanks to the network of rails visible in some of these photos. Thirty different positions are available in order to maximise the observational possibilities.

It’s time to head back down for breakfast, before going back up to the platform for our second live appearance, which is a question and answer session with Gabriel, who is a ‘day astronomer’ this week, one of those who makes the daytime calibrations so that the night-time observations go smoothly. Claudio is team coordinator this week, and his job is to take care of the smooth running of the day, both in terms of science and of logistics.

The wind is impressive up there, 18 metres per second, or almost 65 kilometres per hour. The sunshine is intense, and skin dries in a matter of minutes. The conditions are extreme, but for me it’s a huge pleasure to be back there, with these people, to interact with Joe and to answer the public’s questions. I think it’s obvious in the video, but the magic of Paranal is also the mutual respect and shared mission of the people who work there. I take the opportunity to thank all of those who have welcomed me into their offices, workshops and their telescope, and who have made me feel at home on this mountaintop in the middle of the desert.

The image that comes from the morning’s observations is put online by ESO around 11am. Quite simply superb.

Crédit: ESO/B. Bailleul

Once the live show is over, I leave the VLT platform with regret, for the last time during this trip.

Back to the residence for lunch and to have one final ice cream on the terrace, in the sun, looking at the surrounding mountains.

There’s just enough time left to take a few photos, and to return once more to the pool.

Suitcase packed, it’s already 4pm, time to go, and not without regrets. Picking up the hire car, handing back my badge at the reception, looking one last time towards the VLT platform, stopping to take a photo of Armazones (the future home of the E-ELT) and picking up a few rocks.

Leaving the desert, returning to civilisation, crossing Antofagasta by the coastal road, taking the plane and finally a taxi to the ESO guest house at Santiago. It’s 11pm.