What’s Up In the Sky, March 2008
March gives us the opportunity to see an object that man has observed since he began to look at the sky. In dark skies without light pollution the blurry glow they called Praesepe or the Beehive in the constellation Cancer can easily be seen, Cancer was one of the 48 constellations on Ptolemy’s list, and Messier gave the glowing blur the designation we know it by today M44.
Galileo discovered the four inner moons of Jupiter on January 7, 1610. The next night they were independently discovered by the German astronomer Marius, who named them Io, Europa, Ganymede and Callisto, in outward order from Jupiter. Galileo was observing Jupiter, which in March of 1610 was in the constellation Cancer, when he decided to take a look at that blurry object and was able to make out 40 stars. However it was Jupiter and its moons, that Galileo had the most interest in, especially the one closest to Jupiter.
Galileo observed that Io was eclipsed by Jupiter every forty- two and a half hours and thought that fact could be used to solve a big problem in navigation, determining longitude. He had found a universal clock, and he would become rich.
Clocks of Galileo’s era were weight or pendulum driven and the ships motion at sea made them useless. But, here was an event that could be seen from anywhere, tables could be made up and….no one bought the idea. Galileo would continue to work on the idea off and on until his death in 1642.
After Galileo’s death, a fellow Italian Giovanni Domenico Cassini studied Galileo’s idea and was able to make successful measurements of longitude using eclipses of Jupiter’s moons as a clock. Cassini is credited with discovering Jupiters red spot and four moons of Saturn and, the division in Saturn’s rings now named for him.
In 1671 Cassini was made director of the Paris Observatory and using Galileo’s clock made the first accurate land survey of France. The first country to have it’s borders done with such accuracy. The king of France was upset because it turned out to be smaller than expected.
Now on the scene comes Danish astronomer, Ole Romer. He along with Jean Picard made 140 observations of eclipses of Jupiter’s moons and were able then to compare them to the Cassini’s observation over the same period and calculate the difference in longitude between Paris and Uranienborg, Denmark.
Cassini had noticed discrepancies in his measurements that Romer realized were caused by where the Earth was in its orbit either approaching Jupiter or going away from it. He had just discovered that light had speed. The further away the Earth was from Jupiter the longer it took light to reach us. Until then light was thought to be infinite.
Again, for cartography the method worked very well, for navigation at sea not as well.
In May of 1804 28 men and a big dog began a journey up the Missouri River to map and explore the land recently purchased from France. The story of the Lewis and Clark expedition will never bore me. However it was Lewis that had gotten the crash course in navigation by Andrew Ellicot, America’s leading astronomer. In Philadelphia Lewis had purchased the most accurate chronometer he could find. Lewis could identify stars, among the stars he used for measurement were Antares, Altair, Regulus, Spica, Pollux, Aldeberan, and Fomalhut. Also he walked the grounds of Monticello at night with Thomas Jefferson as his guide to the sky. Position difference between the Moon and stars were calculated with a sextant and also an old idea going back to Galileo was also used too, the eclipses of the moons of Jupiter.
Two hundred years after the expedition Lewis and Clark’s readings were checked against modern methods. The accuracy was astounding within a few hundredths of a degree at most. One would never know from those readings how arduous that trip was. It’s interesting to think that Lewis’s accuracy had something to do with a guy named Galileo that turned his telescope toward Jupiter on a January night in 1610. Marv
March 5 The waning crescent Moon is close to Venus and Mercury in the east at dawn.
7 New Moon,
8-12 Mars is within 2 deg. of the open cluster M35 in Gemini.
9 DAYLIGHT-SAVING TIME BEGINS 2 a.m.
14-15 The Moon a degree north of Mars.
18-19 The Moon near Regulus and Saturn.
18-28 Mercury and Venus are less than 2 deg. apart in the dawn sky.
19 Spring arrives in the northern hemisphere.
21 Full Moon.
March 23- Apr, 6 Look for the Zodical light.
27 The Moon passes 1 deg. below Antares.
