#christopher clavius

The Fab Four: Clavius (lower right), Maginus (upper right), Tycho (upper left), and Longomontanus (center left) // Antonio Grizzuti

Happy birthday to Christopher Clavius (March 25, 1538-February 6, 1612), the German Jesuit mathematician and astronomer. And now, ladies and gents, here are some fun facts:

History doesn't know his actual German name. It could be Christoph Clau or Klau. It might be Schlüssel, which is German for "key", which in turn is "clavis" in Latin. But really, it's all speculation.

At the age of 17, Clavius joined the Jesuit Order, which was founded when he was a child.

While studying at a Jesuit college in Portugal, he excelled in math. Upon observing a total solar eclipse in 1560, he decided that astronomy would be his life's work.

As a professor at the Collegio Romano in (you guessed it!) Rome, Clavius taught mathematics and wrote textbooks, including works on algebra, the astrolabe, and practical arithmetic and geometry. He also did his own version of Euclid's Elements; that probably contributed to him being called "the Euclid of the sixteenth century."

Clavius was the senior math guy on the commission that reformed the calendar in 1582. This gave us the Gregorian calendar that most of the Western world uses to this day. Check out my previous post on this subject.

In his astronomical works, Clavius was geocentric in his opposition to the Copernican model of the universe for reasons both scientific and scriptural. He remained an everything-rotates-around-the-Earth guy until near the end of his life.

He budged on the matter. A little. Well, not quite, maybe. Clavius and Galileo had a mutually respectful relationship, and Clavius was rather thrilled (in his cautiously Jesuit way) with Galileo's groundbreaking observations of Jupiter's moons and other wonders. In 1610, during Galileo's visit to Rome, Clavius and other scientists confirmed the existence of Jovian satellites and the phases of Venus, which contradicted the Ptolemaic view of the cosmos. But the geocentrism-vs-heliocentrism debate raged on.

Clavius also seemed to take this skeptical-but-delighted approach to Galileo's telescopic observations of the Moon's rough surface. He wrote that "when the Moon is a crescent or half full, it appears so remarkably fractured and rough that I cannot marvel enough that there is such unevenness in the lunar body."

Speaking of the lunar body, Clavius was honored with his own crater formation on the Moon, as you can see above. Largest to smallest, the craters are designated Clavius D, C, N, J, and JA. Fans of 2001: A Space Odyssey might recognize this lunar location as the setting for Clavius Base, a human colony featured in both the film and book.

Feel free to contact me if I'm getting any of this wrong. I'm no Clavius.

Leap Year  

So I came across this explanation concerning Leap Year and the Gregorian Calendar that we currently use in our day-to-day activities from the Your Wednesday Briefing from February 24, 2016 edition of the New York Times. Here is what the post states:  

Feb. 29 appears on the calendar this month, as this is a leap year. That got us wondering: How did we end up with this calendar and its periodic recalibrations?

While China and other countries recently celebrated Lunar New Year, and Iran is preparing for Nowruz on the first day of spring, most of the Western world abides by the Gregorian calendar.

Pope Gregory XIII issued a papal bull, or proclamation, outlining the new calendar on this day in 1582 ***Editors Note aka HistorySisco: The papal bull was entitled Inter Gravissimas - Establishment of the Gregorian Calendar [Papal Bull] February 24, 1581/2***. It refined the Julian calendar that was in use at the time by synchronizing it more precisely with the Earth’s movement around the sun.

While the Gregorian calendar took the pope’s name, its adoption was heavily influenced by Christopher Clavius, a German priest and astronomer, and Aloysius Lilius, an Italian doctor.

Like the Julian calendar, it ensured that every year divisible by four would be a leap year. But it added an exception: Years ending in two zeros would be a leap year only if divisible by 400.

This more sparing use of leap years lets the calendar resolve a discrepancy with the solar year in the Julian calendar. (That explains why Eastern Orthodox churches, which still observe the Julian calendar, celebrate Christmas in early January.)

Britain, along with its American colonies, adopted the Gregorian calendar in 1752. Russia waited until 1918.

Even with the elaborate system of leap years, the calendar will still require another tweak. A day will need to be dropped in about 3,000 years.

For Further Reading:

Leap Year 2016: Why does February have 29 days every four years? by Rozina Sabur, Cameron Macphail and Juliet Eysenck from the Telegraph website dated 29 Feb 2016

The Gregorian Calendar from Time and Date.com