Lick Observatory, pictured above, is situated in the mountains east of San Jose, and when it was constructed in 1887 it was the world’s largest refracting telescope (a title it held for about 10 years).  Its benefactor, James Lick, made his fortune buying up real estate during the California Gold Rush (and incidentally, was the one who convinced his Peruvian friend Ghirardelli to move to California and start selling chocolate).  According to the historian-in-residence, the 40-tonne telescope itself is so finely balanced that it can be turned around by hand.  Though to reach the eyepiece, you need to move up the entire wooden floor surrounding the base of the telescope, a feat that’s possible through a mechanical water elevator.

The observatory also recently dug up the only known seismogram of the 1906 California earthquake recorded in North America:

As it turns out, 2009 marks the 400th anniversary of Galileo’s telescope (though he wasn’t the first to invent one - historical evidence suggests that honor goes to either Hans Lipperhey or Zacharias Janssen).  The progress of astronomy over time could be measured by tracking the resolving power or light-gathering ability of telescopes built:

“A telescope’s ability to detect fine detail in object at distance is known as resolution or resolving power… resolution is inversely proportional to the size of a telescope’s primary mirror.  A 5-inch telescope… could distinguish two quarters placed an inch apart from 3 miles away.  A 1.3-meter telescope could distinguish heads from tails on the quarters.  A 10-meter telescope could read the letters on the quarter spelling out ‘in God We Trust’… bigger telescopes can also see fainter objects.  The light-gathering ability is determined by the area of the primary mirror.” - Robert Duffner, the Adaptive Optics Revolution

Based on the list here, you can see the progression over time:

One should note that most of the new telescopes achieve their apertures through either segmented mirrors (a bunch of small mirrors put together) or optical aperture synthesis (mirrors separated by some distance joining to create a single image through interferometry) - simply because it’s prohibitively expensive to make large, smooth, light-weight concave mirrors with the accuracy demanded by telescopes (the mirror surface for one of Keck’s telescopes required ion milling to within a few nanometers).  Even with all this, if it weren’t for adaptive optics, the huge telescopes would be generating blurry images due to atmospheric turbulence (which is why astronomers tried to bypass this by creating Hubble and launching it into space).  It was originally thought of by Horace Babcock in 1953, developed by DARPA at the Starfire Optical Range, and improved by Will Harper’s sodium waveguide laser concept.  Modern telescopes also use liquid-nitrogen-cooled CCDs (which increases their sensitivity to photons) to capture digital images of the stars.

What’s next?  The 30-meter telescope on Mauna Kea, the Giant Magellan Telescope (a description of how they make their mirrors), the James Webb Space Telescope (the successor to Hubble).  In addition, alternative designs using liquid mirrors and membrane mirrors are being developed.