EPT![[image loading]](http://i.imgur.com/LDgn9Eu.jpg)
MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov Telescope, moreorless) is (as far as I know) the second largest imaging gamma-ray telescope in the world. These things work by observing the Cherenkov light created in the atmosphere by the particle showers that happen when a very high energy photon (far harder than your common X-ray) hits an atom of the air - the idea is very similar to our own Auger project, you just use the huge volume of atmosphere above you to make you effective detector much bigger.
![[image loading]](http://i.imgur.com/1PHPDpk.jpg)
The MAGIC itself isn't exactly small either, though - they have two telescopes, each is 17 meters across, larger than any astronomical telescope in existence (incidentally, the largest such telescope is GTC, located in the dome on the horizon in the last picture of the post). The price to pay is that they are not capable of traditional imaging, the resolution of the optics is worse than your binoculars ... but for the gamma showers it's enough. It's the size that matters, because the Cherenkov light is extremely faint and you need to collect from a large area to see anything.
![[image loading]](http://i.imgur.com/C2EN1YF.jpg)
But this situation, when gamma telescopes are larger than astronomical ones will not hold for long - a 40-meter telescope is now being built in Chile. To help it achieve best results, a system of adaptive optics is being developed, including a 20-watt sodium laser which creates artificial stars via excitation of a sodium layer high in the atmosphere. This laser is now being tested here, alongside the 4-meter William Herschel Telescope (the white dome at the base of the beam). I didn't even notice in the field, but in the same picture, you can see a much fainter green beam parallel to the yellow one - that's the MAGIC lidar, a laser system for monitoring atmospheric transparency. The next picture shows it better.
![[image loading]](http://i.imgur.com/YU3hSok.jpg)
As the Moon is near full, the dark time between the sunset and the moonrise was only an hour yesterday. When the Moon comes out, the landscape changes dramatically and suddenly, you see things like if it were daylight. It's a nuisance for the telescopes, but even MAGIC can operate under moonlight thanks to having a special filter to suppress the moonlight while letting most of the Cherenkov light through. Even despite best efforts, the Moon runs are of lower quality - but if you have a pair of 17-meter telescopes, you want to squeeze them as far as you can.
![[image loading]](http://i.imgur.com/e7wyOmb.jpg)
Our trip here to establish a location for our own atmospheric-monitoring telescope has been a moderate success. We confirmed that our building technology works in the soil here and found a very suitable location, but there are still many permits to get and a lot of administrative issues. But it seems likely that we are coming back soon, this time with an actual telescope to build.
