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University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Great Plains Quarterly Great Plains Studies, Center for 1993 How Far West Am I?: The Almanac as An Explorer's Yardstick Arlen J. Large The Wall Street Journal Follow this and additional works at: https://digitalcommons.unl.edu/greatplainsquarterly Part of the Other International and Area Studies Commons Large, Arlen J., "How Far West Am I?: The Almanac as An Explorer's Yardstick" (1993). Great Plains Quarterly. 752. https://digitalcommons.unl.edu/greatplainsquarterly/752 This Article is brought to you for free and open access by the Great Plains Studies, Center for at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Great Plains Quarterly by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. HOW FAR WEST AM I? THE ALMANAC AS AN EXPLORER'S YARDSTICK ARLEN]. LARGE On 14 September 1494, three ships from nearest tip of Europe. From that Columbus tried Spain lay anchored at the southeastern tip of to judge how far west he was at this stop on his Hispaniola. Their admiral, Christopher Co­ second voyage to America. lumbus, looked up at a full moon expecting More than three hundred years later something to happen, and it did. Meriwether Lewis made the same kind of cal­ Darkness nibbled at one edge of the lunar culation at his winter fort in modern North disc, the start of an eclipse predicted in an Dakota. His almanac forecast the time in Green­ almanac carried by the Admiral. The book had wich, England, that a lunar eclipse would end been prepared twenty years before by a on 14 January 1805. When the American ex­ Nuremberg mathematician called Regiomon­ plorer saw the moon escape from the same tanus. The almanac gave the date and time of eclipse, he noted his North Dakota time and that eclipse as clocked from Europe. Watching figured his longitude was 99°27' west of Green­ sand in an hourglass, Columbus decided his wich. local time for the event lagged five and a half Both Columbus and Lewis investigated dis­ hours behind Portugal's Cape St. Vincent, the tant places at a time when astronomy was considered the main scientific way of fixing their positions. Historians of American explo­ ration know well the names of other travelers who were guided by the sky: Alexander Mackenzie, John Evans, David Thompson, Zebulon Pike, Stephen Long, John Charles Arlen]. Large is a former reporter for The Wall Street Fremont, and John Wesley Powell. Journal, 1956-86, and a past president of the Lewis and Like Columbus and Lewis, these explorers Clark Trail Heritage Foundation. needed almanacs predicting the times of various celestial events to help locate their place on earth. Their travel accounts, however, rarely [GPQ 13 (Spring 1993): 117-131] explained how almanacs contributed to their 117 118 GREAT PLAINS QUARTERLY, SPRING 1993 own measurement of daily progress and to the Toledo, the Azores, Copenhagen, Paris, and maps they brought home. For example, many of others. The first English prime meridian ran the mysterious columns of astronomical digits through the dome of St. Paul's Cathedral in filling the Lewis and Clark journals have mean­ London before being switched to suburban ing only when linked to the almanacs they Greenwich. Not until 1884 did an interna­ carried. To understand how explorers navigated tional convention formally ratify Greenwich as America historians therefore might find it help­ the world's prime meridian, from which 180 ful to review the general concepts of antique degrees of longitude diverge east and west. 2 almanac usage. And that, in turn, requires an The idea of locating a place on Ptolomy's acquaintance with some European almanac sa­ coordinate grid by astronomy also had ancient vants-Giovanni Domenico Cassini, Tobias roots. Geographers quite early realized they Mayer, Nevil Maskelyne-whose names aren't could measure north-south travel by tracking often linked with the Great Plains and Rocky the elevation of the North Star at night or of the Mountains. sun at noon after adjusting for seasonal varia­ The kind of almanac used by navigators is tions. That gives latitude in degrees from the properly known as an ephemeris, which forecasts equator; the earliest almanacs provided naviga­ the celestial positions of the sun, moon, and tors year-round tables of the sun's seasonal planets. For a long while astronomy navigation height needed for this calculation. For the coexisted with the spookier practices of astrol­ harder task of measuring east-west movement, ogy; the Regiomontanus almanac, for one, Hipparchus of Nicaea theorized as early as 150 bragged that it could divine the future and B.C.E. that a distant celestial occurrence like a predict the weather. The Paris Observatory lunar eclipse could be used to establish longi­ started compiling the first real astronomical tude. almanac in 1679, but it was the Royal Green­ The basic principle underlying the use of wich Observatory's Nautical Almanac and Astro­ astronomy to get longitude is that time equals nomical Ephemeris that became the prime posi­ distance: in one hour of time, the earth rotates tion-fixing handbook for the explorers and through 15° of longitude. That's the rate at mappers of North America's interior. which the moment of local noon moves west­ In calculating how far they had come from ward as the earth turns beneath the sun. Thus home, these investigators relied-as we still each hour of difference between the local noons rely-on conventions inherited from the an­ of two observers equals 15° of longitudinal sep­ cients: a global grid of north-south and east­ aration. The function of a celestial event that west coordinate lines developed by Claudius can be seen simultaneously in places distant Ptolomy in the second century C.E. for the from each other is to signal the observer at Mediterranean world.! The arcing lines of each place the exact instant at which to mark Ptolomy's latitudes and longitudes chopped the the local time shown on each respective clock. arcing lines of his grid into 360 units or degrees, In practice an almanac substitutes for the home­ an inconvenient legacy of old Babylon. base observer, giving the traveling observer a Ptolomy decided degrees oflongitude should reference against which to compare local time. be counted eastward from a base meridian run­ The non-astronomical method of carrying a ning through the Canary Islands off the coast of chronometer set on the time of a known longi­ Morocco-to him the edge of the western world. tude serves the same function. Many mapmakers continued to count 360 de­ That's the theory, anyway. As will be seen, grees all the way around the globe from the precise position-fixing often was elusive in prac­ Canaries well into the eighteenth century, tice during the age of exploration. A traveler which is why North American longitudes on could be misled by the built-in error of his own old maps often numbered in the high 200s. almanac if it placed the moon just a smidgeon Rival prime meridians proliferated, including away from its real location. Instruments still HOW FAR WEST AMI? 119 weren't terribly accurate, and paperwork mis­ earth casts a fuzzy-edged shadow on the moon, takes could snare busy seamen, soldiers, and and Lewis had to make a subjective decision traders who may have had little practice in about timing the shadow's final departure. Be­ celestial mathematics. sides that, it would appear Lewis left out an Both Columbus in 1494 and Lewis in 1805 additional step in his calculations needed to put tried to exploit the theory with lunar eclipses, his local time on the same footing as the Green­ and their answers were both off the mark. Co­ wich time shown in his almanac. That addi­ lumbus faced greater disadvantages, for his tional adjustment alone would have brought hourglass was too crude for comparing his local him closer, but still thirty miles too far west of time with the eclipse time shown in Regio­ his true position.6 In drawing his map of the montanus's almanac. Also, his result depended area, co-commander William Clark decided to on accurate almanac predictions of the moon's borrow a better longitude derived from the work orbital motion, and Regiomontanus made his of a previous explorer, David Thompson. forecasts without benefit of the later writings of N icholas Cop~rnicus, Johannes Kepler, and Isaac For much of human history the difficulty of Newton on how orbits really work. finding longitude wasn't a terribly disabling If Columbus's local time of the eclipse was problem. Mediterranean sailors going east or five and a half hours behind his chosen base west needed only to keep the shore in sight. meridian of Cape St. Vincent, he would have Norsemen pushed their boats westward from been at about the same longitude as New Or­ Scandinavia to Iceland to Greenland in man­ leans-1500 miles too far west. Everybody has ageable stages by keeping Polaris steady off wondered how the great navigator could have their right shoulders. By around 1000 C.E. they been so wrong. Samuel Eliot Morison, the required only a final westward hop of about Admiral's best-known chronicler, has suggested three hundred miles across Davis Strait to bump Columbus gladly embraced the mistake because into "Helluland," today's Baffin Island. From it reinforced his conviction that he was on the there they turned south to their short-lived doorstep of Asia.3 Ernst Zinner, Regiomon­ L'Anse aux Meadows settlement in Newfound­ tanus's biographer, has offered a more specific land.

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