The world's largest telescope is currently being built in Steward Observatory, Arizona. The first (and the most critical) component of the telescope is to be casted soon; 8.4 meter diameter mirrors, which will more than quadruple the power of today's best observatories:):). The mirror will be created by pouring liquid glass onto a huge mold, the last of whose 1,681 ceramic fiber cores was recently added.

Installing the core (Courtesy: University of Arizona)
The mirror is for the Giant Magellan Telescope (GMT), which when completed will have seven of such large mirrors! The mirrors will give GMT four-and-one-half times the collecting area of any current optical telescope and the resolving power of a 25.6-meter (84-foot) diameter telescope, or 10 times the resolution of the Hubble Space Telescope:):).
Obviously, to build such a large, blemish-free mirror is a Herculean task. The Mirror Lab will start heating the furnace July 18, 2005. It takes six days for the glass to reach peak temperature at 2150 ºF (1178 ºC). At this temperature, the glass begins to flow like honey at room temperature. The thick liquid glass flows between the hexagonal cores in the mold to create a honeycomb structure. The oven's rotation rate determines the depth of the curve spun into the shape of the mirror, or the mirror's focal length. The whole process will take 11-12 weeks.
The GMT is slated for completion in 2016 at a site in northern Chile. With its powerful resolution and enormous collecting area, the GMT will be used to detect extrasolar planets, understanding the formation and evolution of galaxies, probing dark matter and dark energy, finding the link between black holes and galactic bulges, and so on and on:).