Around OCA for April, 2005
Posted On April 2, 2005
By Barbara Toy
Starting off this month with something a little different than our usual fare
Astronomy and the Lewis and Clark Expedition
I've been thinking quite a bit about Lewis and Clark mainly because of a CD I've listened to so many times on my way to and from Anza (and other places) that I've lost count, that was put together to commemorate the bicentennial of their famous expedition. One song starts:
he river sorely tested us that spring of 1804
When we set out to explore Louisiana
I don't know why that drove the date home, but 1804! Cosmically speaking, only the blink of an eye, but what a different world they had! Jefferson was president, California was part of Mexico, our Gold Rush was still 45 years in the future, and the United States was just beginning its westward expansion with the Louisiana Purchase. In Europe, France made Napoleon its emperor, and he was pursuing his own expansion plans. In astronomical circles, William Herschel had just published his third list of nebulae, and had shown that some double stars were true binaries that orbited each other, not just visual binaries that happened to be along the same line of sight. Frederich Wilhelm Bissel was calculating the orbit of Halley's comet using observations made by Thomas Herriot two hundred years before, and William Wollaston had just noted the existence of dark lines in the solar spectrum, though nobody yet had any idea what they meant. 1804 also saw the discovery of the third and fourth known asteroids (Juno and Vesta; the first two were Ceres in 1801 and Pallas in 1802).
Artificial lighting of the time was by flame candles, oil lamps and lanterns of various types, and wood or coal fires were still the main sources of light when the sun or moon weren't available. Experiments had started on lights fueled by coal gas, but true gas lights were still several years away. Night skies over the cities of the time might have been smoky, but were still very dark. And the night skies over the Lewis and Clark expedition must have been darker still when they weren't clouded over or filled with moonlight, of course. So, naturally, the historically-minded astronomer wonders about what astronomy they might have done on that expedition of discovery
Meriweather Lewis bought a six inch long telescope in Philadelphia among his other supplies, about the length of finderscopes on many modern amateur telescopes. He also had at least one that was15 inches long, which would still be a pretty short telescope. Unfortunately, I couldn't find any direct information about the apertures, even though there's a 15-inch telescope from the expedition at the Athenaeum in Philadelphia. One refractor from that era with a 3-inch primary is 35 inches long, and another with a 4-inch primary has a 60-inch focal length (see http://www.antiquetelescopes.org/19thc.html and the Kenyon College site given below). These imply that a 15-inch tube had a correspondingly smaller primary "fast" short-tube refractors are a more modern phenomenon. As additional comparisons, I have a 3-inch refractor with a 31-inch tube, and the finder for my ETX is four inches long with a 1-inch aperture overall, the indications are that the expedition's telescopes were of pretty small aperture, most likely one to two inches. There are also references to the expedition using "spyglasses," one of which was carried by Captain Clark and used to scan terrestrial objects, including parties encountered along the way again, most likely of pretty small aperture. I've found no descriptions of the optical qualities of their telescopes, even of the surviving telescope at the Athenaeum, but, even if their optical equipment wasn't of the size or quality we would expect to see at a modern star party, they clearly did have a number of telescopes of various types along with them.
Sadly, if anyone used the telescopes for astronomical viewing beyond the navigational requirements of the expedition, it doesn't seem to be recorded in the expedition journals (though there's a description of Northern Lights observed on the night of November 5, 1804, from Fort Mondan). Lewis received training in astronomy and navigation in preparation for the trip, and did use the sun, moon and stars regularly to determine their location, using the same techniques more often used at sea. This was by Jefferson's specific directive, so they would have a better record of the locations of important points they found along the way than if they made their maps based only on their observations of the terrain without celestial references. To make the necessary readings, Lewis brought along a number of specialized pieces of equipment, in addition to the telescopes a quadrant, a sextant, an octant, a surveying compass, artificial horizons and a chronometer and took frequent readings to determine the expedition's latitude and longitude.
Latitude was the easier of the two measurements, as it was read off of the position of the sun using the sextant or octant, but properly measuring longitude required an accurate chronometer to provide Greenwich time, which was a problem. As a check on the local time, they used a technique of measuring the altitude of the sun when it was at equal distances on either side of the meridian, noting the times, and averaging to get the time for local noon. They also used the angular distances from the moon to planets and stars to determine the timing of certain events or configurations according to the tables in the Nautical Almanac and Astronomical Ephemeris along with proportional logarithms given in Maskelyne's Requisite Tables for times not shown in the Almanac; the difference between the time per the Almanac and their local time would give their longitude. These were exercises that took a lot of computation after they got the actual readings it seems that this is one aspect of pulling information out of astronomical observations that hasn't changed much in 200 years. Unfortunately, for a number of reasons (including atmospheric refraction, changes in the equipment with temperature and moisture levels as well as wear and breakage, problems with the chronometer, and inaccuracies in the tables), most of the readings that Lewis and his assistants got were not accurate enough to give pinpoint locations (several were miles off), but they were precise enough that most of the locations could be identified by people looking for them later, so they did serve their purpose.
here's nothing like a big anniversary to turn people's attention to particular events, and we're right in the middle of the bicentennial of the Lewis and Clark expedition (which took place from 1804 to 1806). If you're interested in any aspect of the expedition, there are lot of different sites available on the Internet to help you out. I'm particularly indebted to Discovering Lewis and Clark, http://www.lewis-clark.org/ , Lewis and Clark Historical Articles from the Bureau of Land Management, http://www.id.blm.gov/lc/ , the Philadelphia Chapter of the Lewis and Clark Trail Heritage Foundation, http://www.lewisandclarkphila.org/, the Lewis and Clark Internet Archive, http://www.lcarchive.org/ , and American Journeys, a digitized collection of original documents from America's early days, including the full published journals from the Lewis and Clark expedition (http://www.americanjourneys.org ). Another useful site, though not specifically on Lewis and Clark, is at http://www.answers.com/ , which has all kinds of interesting information, such as what was happening when. Kenyon College has a lot of pictures about equipment used in the early days of physics on its site, including optical equipment; see http://physics.kenyon.edu/EarlyApparatus ; the part of the site on telescopes is http://physics.kenyon.edu/EarlyApparatus/Optics/Telescope/Telescope.html , which for those interested in true classics includes pictures of several different Clark telescopes. And the album I started off with is "Most Perfect Harmony," Lewis and Clark: A Musical Journey by the Discovery String Band, a great sing-along album for those long trips out to the dark site of your choice.
[Thus endeth the educational portion of this column. For further educational content, you might want to check out Don Lynn's Astrospace Update]
urning to more current matters
The 2005 Messier Marathon and Clean-up Day
Every year's Messier Marathon seems to have its own twist, and this year's was no exception. Those who were out at Anza the night before the Marathon, which was the night of the March general meeting, have told me (some with from my perspective, anyway unnecessary glee) that it was a wonderful night out there, and there have been pictures posted to the website fr