Wednesday, January 16, we went to Lowell Observatory's campus on Anderson Mesa. Their original campus on Mars Hill, which we visited Monday, directly overlooks Flagstaff, so as the city grew, the serious astronomy moved ten miles or so away to the mesa. We met up with the group from MIT again and got a tour of the mesa. Our guide showed us two optical telescopes, and we went on the catwalk along the outside of one of the domes.
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| It's hard to get good pictures of big things in small spaces, but here's a wonky mosaic of the first telescope we saw. |
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| This is one of the domes at Lowell. |
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| Taking a panorama while walking around the dome's catwalk didn't work perfectly, but this is what we saw around us. |
The second telescope's mirror had been recently removed and sent off for resurfacing at the Flagstaff station of the US Naval Observatory (which we visited Monday), which meant we got to see the assembly that holds the mirror so precisely in place. The guide mentioned that the mirror had been dropped on its way to resurfacing and a part of the mirror would no longer reflect light, making my own mishaps in Calvin's observatory seem much less severe.
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| This is the mirror-holding assembly. |
Next we were shown the Navy Precision Optical Interferometer.
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| The interferometer |
This is a virtual telescope made of many small telescopes. Maybe a foot in diameter each, these telescopes are placed hundreds of feet apart along an infrastructure of vacuum pipes. The light from the telescopes is sent through the tubes to the center of the system where it is combined to produce a final image. The trick is that on the way to recombination, all the light from the distant telescopes must travel exactly the same distance to within ten nanometers or so--a fraction of a wavelength--despite coming from telescopes hundreds of meters apart. To do this, light from near telescopes is sent through delay lines--tubes with mirrors at the end--while light from distant telescopes catches up. This gets the path lengths much closer. Then the light from each telescope is sent into more delay lines, where three motors, each with less range but more precision than the last, move a mirror to the exact position needed for each telescope. (We saw one of the nested cart assemblies that the motors move at the Naval Observatory.) This ensures all the light travels the exact same distance, no matter which telescope it came from.
This device gives images with the resolution of a telescope whose mirror's diameter is the same as the distance between the small telescopes, which is much larger that any existing telescope by far. While the interferometer has this resolution, it sacrifices a lot in sensitivity and detail because it collects so little light. Still, they are able to directly measure the sizes and shapes of some stars, which is really impressive. Additionally, the interferometer uses lasers to measure the exact direction each of the mirrors is pointing with incredible precision, allowing it to make extremely precise measurements of stars' positions. The Navy, it turns out, still uses star maps for navigation. This is one example of the interplay between military and scientific goals that we've seen at some of the places we've visited, such as Los Alamos.
After lunch, we went to the Discovery Channel Telescope, about twenty miles further from Flagstaff. One of the staff members brought us up into the dome to show off the telescope. While all the large telescopes we've seen have had skeletal frames rather than a full enclosure like Calvin's telescopes, the Discovery telescope was especially unenclosed and we were able to see the surface of the four-meter-diameter mirror. (Our guide even offered to let us reach out and touch the mirror, as long as we didn't mind him cutting our fingers off.) He rotated the telescope pier, letting us ride on the spinning floor, and pointed the telescope down a bit to give us a better view of the mirror. We were also able to climb to platforms on the edge of the telescope and look down on it. The experience felt much more open than the other telescope tours we've had, like they were really excited to show off every part of this brand-new telescope. (When this trip happened before, four years ago, they saw the mirror being made at the U of A's mirror lab, so it's really new.)
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| The dome, which isn't quite dome-shaped |
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| On the ground floor looking up at the base of the telescope pier |
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| The Discovery Channel Telescope |
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| The instrumentation on the bottom |
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| A glimpse of the mirror |
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| The top of the telescope. (The cone is a closed cover.) |
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| A bunch of wiring mid-way up the side |
Once it began getting dark, the coolest part of the day began. Since the telescope is so very new, it's still being tested and calibrated and no real science is going on yet. It also has an eyepiece, unlike almost all large telescopes. This all means that for now, they can let groups like us look through the largest telescope that perhaps we'll ever look through! So they began starting equipment and opening things up so equipment could cool to the outside temperature. (Christian and I got to push the buttons to open the seven garage door-style openings around the dome that let cool air in!) Once it was thoroughly dark, we got to look at Jupiter and the Orion nebula. The telescope can cool off very quickly, but the mountain takes much longer, so the warm mountain with the cool air was driving air currents that, along with the wind, blurred the image, but the view was still fantastic. There was texture in the Orion nebula! We had to stop after seeing these two things to give the telescope back to its operators, and we were just about too cold to continue anyway--lots of people were dancing and singing show tunes to try to keep warm. But it was an amazing, one-of-a-kind experience.
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| Look, that conical cover is open now! |