Sunday, January 15, 2012

Giant Magellan Telescope ~ The Flame is burning

What a great weekend for astronomy related activity so far!  Great observing on Friday night, and then a visit to the Steward Observatory Mirror Lab on Saturday during the casting process for the second of seven mirrors that will become the Giant Magellan Telescope (GMTO). We are now clouded out, so what better activity than writing a blog post?

Click to enlarge
As mentioned, Friday night my good friend Jerry and I drove an hour south of Tucson to a great little spot called Empire Ranch to do some observing.  We arrived just before sunset and stayed until moonrise.  While the seeing (atmospheric stability) was just above average, the atmospheric transparency was excellent with a naked eye limiting magnitude of 7+ at the zenith.  The zodiacal light was quite bright shining from the horizon all the way up through Jupiter at the meridian.  While Jerry was busy continuing his detailed observations of globular clusters within the Andromeda Galaxy (not for the faint of heart!), I spent a lot of time panning through the winter milky way in Canis Major with my 4 inch f/11 refractor (how often can you see the milky way in this region!?!?).   I had also brought along a Meade 178mm f/15 Maksutov Cassegrain for evaluation and spent time observing Jupiter, M42, and various star clusters.  Later on in the evening, I decided to make a sketch of NGC 2024, nicknamed the Flame nebula, in Orion.  At right is my sketch completed through the Meade 178mm using a Panoptic 35mm eyepiece.  This is a very diffuse nebula that I tried to capture on paper, so be sure to click on the sketch to enlarge.

First GMTO Mirror
Saturday afternoon, Dean Ketelsen had arranged to take a group of Tucson Amateur Astronomy Association Members on a tour of the Mirror Lab.  I had been there a couple times previously, but never while the furnace was in operation.  Dean is a knowledgeable and friendly individual who shares a passion for astronomy and blogging (check out his blog here).  Dean began the tour showing us the first GMTO mirror, which is in the final stages of polishing.  It is always impressive to see an 8.4 meter mirror in front of you, but when considering that this mirror is one of seven that will make up the 24.5 meter GMTO, and that is an off-axis mirror, it gives one pause to consider how cutting edge this project is.  The first mirror is very nearly finished...while not perfectly smooth, the variations that exist are on the order of a millionth of an inch (you read that right).  As this mirror will sit off-axis (in other words, it is not the central mirror of the seven, but one of the six that will surround the central mirror) it requires a very unusual figure and is to date the most challenging mirror that the mirror lab has ever produced.  Here is a piece of trivia that will amaze-  how much aluminum is used to coat a mirror of this size?  Glad you asked!  An amount about the size of a can of soda pop!

For those of you who are interested in the accuracy of the mirror, you can enlarge the image at right, which is a picture I took of a poster sitting next to the first mirror.  The LBT referred to is the Large Binocular Telescope, currently the largest optical telescope in the world sporting twin 8.4 meter mirrors.  Ironically, when the GMTO comes on line it will be competing to retain its position as the largest telescope at 24.5 meters as there is a consortium working to create the "Thirty Meter Telescope" as well as discussion of "The Extremely Large Telescope" of 42 meters!

Continuing on, Dean took us to heart of the days festivities, the rotating furnace containing the molten glass that will become mirror number two.  There was something awe inspiring as we descended the steps into the room.  Not only was it impressive visually, but the sound or the furnace moving and the sensation of the heat radiating from the furnace reminded everyone that we were seeing history.  To stick with the GMTO theme, it was as if we were witnessing construction of the ship that Magellan would sail in the first crossing from Atlantic to Pacific oceans, or in the first circumnavigation of the world.   At left is an image of the furnace as it rotates.   From left to right in the picture are Dean and Melinda Ketelsen, and me with my friend and colleague Cathi Duncan who coordinates outreach for the Mirror Lab (she rocked the weekend!).

A BIG thank you to Dean for arranging this opportunity for TAAA members to experience this historic event.  So what is the next best thing to being there?  A video of course!  I made this short video with my point and shoot camera and uploaded it to You Tube...if your volume is on, you can hear the furnace as it rotates.  Several folks who have seen this video have asked about the speed of the furnace.  As it turns out (pun intended) the furnace speed was about 4.8 mph while I was visiting.


  1. Hi Alan

    Thank you for posting this. Surely was a fascinating event.
    Would have loved to attend the event as well.


    1. It was very cool, and I was thinking about you while we were there. As soon as you have an idea of your visit dates, send me a note!


  2. Had no idea that the furnace rotated that quickly when they were casting a mirror. That's a lot of hardware on that carousel to be spinning so quickly!