Unlike the situation with latitude, where every line on the earth corresponds to one and only one line of declination on the sky, lines of longitude do not correspond to any single line of right ascension, since the earth is constantly rotating beneath the celestial sphere. Indeed, this is the principle by which we measure longitude; the rotating earth makes the sky act like a giant clock with the observer's meridian acting like the hour hand. By comparing one's local sky clock with any other standardized clock, one can determine one's distance from that standard clock.
One knows from experience that the earth is divided into time zones, but time zones are a relatively recent invention necessitated by modern society's ability to travel quickly and communicate instantly to distant places. Previously, time was reckoned locally by reference to the sun (``local noon''), so that each community enjoyed a different time from even it's neighboring community. Since the earth rotates 360 degrees in 24 hours, two communities separated by 1 degree of longitude (e.g., Charlottesville and Richmond) had clocks different by 4 minutes.
In this lab, you will measure your ``local noon'' to determine your longitude with respect to the prime meridian - which corresponds to longitude = 0 degrees. The prime meridian was established by convention to be the longitude running through Greenwich Observatory, in Greenwich, England. This is the location corresponding to the world's standard clock, which measures Universal Time or Greenwich Mean Time (GMT). You can determine your longitude by comparing your ``local noon'' to that of the clock in Greenwich, England, which is keeping track of GMT.
Historically, the problem with determining longitude, in the days before long distance communication was feasible, was how to know what the time was on the standard clock. Ideally, a ship at sea would have on board a clock synchronized to the Greenwich clock (or some other port of known longitude), and comparisons to this clock could be made at local noon on the sea. However, until about a century ago, timepieces were simply not accurate enough, and the mechanisms were notorious for losing or gaining time, especially with changes in temperature, humidity, and turbulent seas. The number of ships lost at sea due to navigational errors in longitude became so problematical, that in 1714 Queen Anne of England offered a prize of 20,000 pounds sterling to the first person that could solve the ``longitude problem'', defined as being able to determine one's longitude to one half degree, or 34 miles! You will be able to do much better than this in this lab. The longitude prize however was not claimed for some 50 years (the fascinating story of the ``longitude prize'' is given in the book ``Longitude'', by Dara Sorel).
For our clock, we will use the broadcast signal on WWV radio (broadcasted at 2.5, 5, 10, 15, and 20 MHz).