Steward is one of the observatories joining together to build what is known as the Giant Magellan Telescope, or GMT. The GMT will be made of seven round mirrors for a total collecting area equal to a single mirror 21.4 meters in diameter, or about 71 feet across. This is over four times larger than the Keck Telescopes, currently the world's largest.
The design of the GMT requires making mirrors in a novel design, called "off-axis" design. This is because six of the seven mirrors are not at the center of the telescope, but rather away from it. A big step toward proving the required technology was taken this last weekend, when the first mirror 8.4 meters (28 feet) across was cast. This involved melting twenty tons of glass to 2150 degrees, and spinning the melted glass at 4.8 RPM. VIPs and Observatory staff were invited to watch this past weekend (though, like I said, I was out of town).
So far, everything has gone well! Now the glass will be allowed to slowly cool over a period of a few months, then the mirror will be examined and ground to its final shape.