This Week’s Penumbral Lunar Eclipse and the Astronomy of Columbus

universetoday.com ^ | October 14, 2013 | David Dickinson on

[BenLurkin]

In Columbus’s day, the Moon was often used to get a rough fix of a ship’s longitude at sea. Columbus was especially intrigued with the idea of using lunar eclipses to determine longitude. If you can note the position of the Moon in the sky from one location versus a known longitude during an event— such as first contact of the Moon with the Earth’s umbra during an eclipse —you can gauge your relative longitude east or west of the point. The sky moves 15 degrees, or one hour of right ascension overhead as we rotate under it. One of the earliest records of this method comes to us from Ptolemy, who deduced Alexander the Great’s position 30 degrees (2 hours) east of Carthage during the lunar eclipse of September 20th, 331 B.C. Alexander noted that the eclipse began two hours after sunset from his locale, while in Carthage it was recorded that the eclipse began at sunset.

Columbus was a student of Ptolemy, and used this method during voyages to and from the New World during the lunar eclipses of September 14th, 1494 and February 29, 1504. Of course, such a method is only approximate. The umbra of the Earth often appears ragged and indistinct on the edge of the lunar disk at the start of an eclipse, making it tough to judge the actual beginning of an eclipse by more than ten of minutes or so. And remember, you’re often watching from the pitching deck of a ship to boot!

Another problem also plagued Columbus’s navigation efforts: he favored a smaller Earth than we now know is reality. Had he listened to another Greek astronomer by the name of Eratosthenes, he would’ve gotten his measurements pretty darned close.

Read more: http://www.universetoday.com/105436/this-weeks-penumbral-lunar-eclipse-and-the-astronomy-of-columbus/#ixzz2hjbIvrwa

[Boogieman]

“Another problem also plagued Columbus’s navigation efforts: he favored a smaller Earth than we now know is reality.”

True, but if he hadn’t believe this erroneous idea, he probably wouldn’t have attempted his voyage, because he would have known it would take 3 times longer to reach the Indies.

[bunkerhill7]

Before 1492, 1490`s? An unsubstantiated story existed that Pinzon, Columbus` financier and captain of the Pinta , supposedly found information in Vatican archives about
“lands to the west.” Dor-Ner p. 73
1490`s? Columbus had set his goal to sail exactly 2,400 miles west from Palos, Spain, which is where the
Bahamas are. How did Columbus know that? P116
1492 Juan de La Cosa is the owner of the Gallega, renamed by Columbus as the Santa Maria; de La Cosa was Columbus` pilot on the Santa Maria P126
1492 Columbus knew the westward trade winds from the Canary Islands- P108
1492 August 3 Columbus sails from Palos, Spain in his 3 ships P128
1490`s Christopher Columbus` original Atlantic logbook, “Diario de a bordo”, and subsequent copies thereof, are lost; parts are in Bartolome` de Las Casas` “History of the Indies”.P122

source:
Dor-Ner, Zvi, “Columbus and the Age of Discovery”, NY : William Morrow & Co. 199167=73

[SunkenCiv]

Thanks BenLurkin. Columbus' belief that the globe was smaller was based on the reality of earlier voyages -- information obtained when he visited Iceland -- but biased by the uninformed Aristotlian view that there was just one landmass and just one ocean. The earlier Platonic view (seen in one of Plato's dialogues) showed that the Americas were rumored, almost 2000 years before Columbus.

[SunkenCiv]

Thanks BenLurkin, extra to APoD.

[Bigg Red]

Cool. We’ll be on the boat that night. Hope to get a good look.