Aiming for the stars

This post will be a little bit irregular, but some people might be interested in the details about the Palomar observatory we visited this week within the frames of the 9th iSAIRAS conference in Los Angeles. We were given a extraordinary behind the scenes guided tour thanks to the kind staff.

The Palomar Observatory is located in between Los Angeles and San Diego, in an altitude of 1700 m (5600 feet). It contains the 200 inches (5.08 m) Hale telescope that used to be the biggest in the world for more than 40 years. George Ellery Hale was a real visionary, and managed to build six times the biggest telescope on Earth (always breaking his own record). This got finished in 1947, and got some mayor reparations since, but has been working very stable, conducting thousands of experiments. Recently, it has been able to capture the world’s clearest space images, overtaking even the Hubble space telescope (that is "only" 94"). The Hale takes advantage of its new adaptive lenses that are compensating for the blurring affect of the atmosphere adjusting the distortion of the mirror at a 2000 reconfiguration/min rate. It uses a powerful laser beam that projects an artificial "star" 90 km high, and can used as a reference.
The 200’ lenses were produced in Pasadena, at Caltech that is the owner and manager or the telescope. It is 23.5 – 19 inch thick, and the biggest surface irregularity is about 10 microns, the focal length is F3.3, looking as far as 11 billion lightyears. I took one month just to melt the glass needed, and then 10 months gradual cooling. While testing, it was replaced with a huge concrete phantom (weighting the same - 14 tons) that can still be seen.
The servos moving the telescope can deal with 150 tons, and it was the first that used pressurized oil to reduce friction. They use the telescope every night if the weather allows (on average 200 nights a year), and to protect it from heat deformation, the interior is always kept at the night time outside temperature (that meant 0C on our visit). There is a dedicated science project for every day, assigned months ahead. If you have bad weather, you have to ask for reschedule.
Besides the Hale telescope, there are other smaller ones nearby. These are all automated, robots are moving the lenses towards the target areas. The new 24” telescope is constantly keeping an eye on Titan’s weather. The 48” Schmidt wide-field telescope is the "rapid reaction force", that is able to focus on any point of interest within 2 min of localization by a satellite. The 20” searches for exoplanets by observing star eclipses, the 60” reflecting has mapped the entire northern hemisphere, and just about to do it again, and there is a fast moving one, that scans the sky three times a night looking for anything new.
Looking to the future, they are testing a new telescope system based in interferometry, and the plans are ready for a 30 m wide telescope, TMT, that would redefine space observation.
The Hale telescope is open for the public, even though it takes three hours to get up to the hills from Los Angeles, it worths the visit.


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