dipper@utastro.UUCP (Debbie Byrd) (09/29/84)
It's easy to find your latitude -- but hard to determine longitude. We'll tell you more about it -- after this. September 29 Longitude and Latitude If you live in the northern hemisphere, it's possible to use the stars to find your latitude -- or approximately how far you are above Earth's equator. The north polar axis of the Earth points almost directly towards Polaris -- the north star. So however many degrees Polaris is above your northern horizon -- that's also the number of degrees you are above the Earth's equator. Here in Austin, we're at about 30 degrees north latitude -- and Polaris is about 30 degrees up in our northern sky. Finding longitude -- how far east or west you are from a given spot on the Earth's globe -- is more difficult. The theory of finding longitude was known for thousands of years -- that differences in longitude correlate with differences in local time. Finding precise longitudes for places on Earth had to wait until two inventions of the seventeenth century -- clocks that kept very accurate time -- and telescopes. The clocks allowed people to pinpoint what time events occurred at their location. Telescopes let them watch celestial events -- which could be seen at widely separated locations at almost the same moment. By observing a celestial event at a given moment at different locations, the difference in longitude can be found. After telescopes were invented, the moons of Jupiter proved suitable for making longitude measurements -- since they could be seen regularly coming and going behind the body of Jupiter itself. Script by Diana Hadley and Deborah Byrd. (c) Copyright 1983, 1984 McDonald Observatory, University of Texas at Austin