Inside the U.S. Naval Observatory

Geoff Chester, a walking history book who's been with the USNO Public Affairs office for 12 years, leads each tour in three parts: observing through the telescope (weather permitting), USNO's mission and history, and "Geoff's Brief History of Time" – a look at how precise timekeeping has developed over the years. First, guests take a short walk through the grounds to the observatory housing the 12" Alvan Clark refracting telescope, built in 1892. Refractors are the telescopes of the romantic astronomy fan; it's the kind Galileo pointed at the sky in 1609 (though much improved by Johannes Kepler's optics research a few years later), featuring an objective lens at one end and an eyepiece at the other. Kepler discovered that flatter lenses created more focused images, but the flatter the lens, the farther away the focal point, making refractors almost comically huge compared to the more modern reflectors, which use mirrors to bounce light back and forth to get that distance without lengthening the body. In other words, a 12" refractor is an impressively big piece of astronomical equipment, and everyone should have the pleasure of seeing (and seeing through) one. In 1952, the telescope was removed from the observatory in favor of a specialized imaging device that took measurements of the Moon in preparation of the Apollo landings, but it was returned in 1980 through the efforts of volunteer astronomers.

On our tour, we were lucky to have a clear sky and Jupiter shining brightly above. We were treated to a couple views; first a wide-angle, in which we could see four relatively tiny moons swung out in their orbits around the gaseous planet. With a switch in eyepieces, we got a close up as the moon, Io, just began to transit in front of Jupiter. As we each waited our turn, Mihran Miranian, astronomer and retired Deputy Director of the Time Service Department, entertained us with the observatory's history, some spectacular digital photography taken with the scope, and answers to our every astronomical curiosity – and our group had many. The Gonzalez family brought their two sons from Bethesda to see the USNO; Nicholas, 9, told me he loved astronomy ("because of all the stars!") and seemed pretty excited to get a real opportunity to see the universe, until his 6-year-old brother Daniel interrupted us for an argument about string theory (I wish I was joking). It was at this point we were briefly interrupted by a "Helo Op" – the Vice President on his way back to the ranch. We were warned not to "rush the windows."

After our fill of Jupiter, we walked down to the USNO's James Melville Gilliss Library, past their six-inch transit circle telescope. If you're a book lover, the USNO library is drool-worthy. Created on a $25,000 budget in 1842, it's now the most complete astronomical library in the country. Copies of books by and about Tycho Brahe, known best for his precise planetary observations and the unusual stories around his death, sit under glass, including Astronomiae instauratae mechanica and his 1654 biography. Here, Chester gave us a fascinating lecture of the history of geographical positioning, from the invention of the complicated system sailors used at sea (involving no less than a chronometer, sextant, and accompanying nautical almanac) all the way up to today's modern GPS systems. Today, the USNO's Master Clock is the "backbone" of the internet (Network Time Protocol servers), digital television, and U.S. GPS. The USNO is part of an international consortium of timekeepers, where the U.S. Master Clock, which derives its time from the mean of 40-80 atomic clocks, contributes one-third the weighted average. To put in perspective how crucial exact time-keeping is to global positioning, Geoff explained that if our GPS satellites were off by one full second, instead of locating your position in the middle of D.C., your car's Garmin would place you approximately 2/3 of the way to the Moon.

The last part of the tour brought us to the sparsely designed (but packed with science) clock room. Unfortunately, guests don't get to see the current timekeepers, which are hydrogen maser atomic clocks. But we do get to see every piece used throughout history, from the "time ball" – dropped from the top of a building in Foggy Bottom at precisely noon each day, so sailors in the harbor could adjust their timepieces – to a photographic zenith tube which took pictures of the stars directly above, to the quartz oscillators that most of us can find in our watches, all the way to the variations of our modern atomic clocks, which redefined our entire concept of the "second." Scientists have been working hard to improve the hydrogen maser clock, and hope to implement the new system, which involves "fountains" of falling atoms, in late 2010. It should improve your GPS by a factor of ten as soon as the clocks are switched on.

Chester's presentation of this sliver of American and scientific history is a highly recommended way to spend a Monday evening. Click over to the USNO web site for more information about tours and events.