As 2020 passes, Jupiter and Saturn get closer to that fatal day (from Earth) when Jupiter overtakes the ringed planet. Although to some it might be considered a "a rare event", it happens once every 20 years. If you need to catch up on the subject, go back and read last month's What's Up? article. The great conjunction has been known to sky watching astronomers for centuries. It was known that the 20-year cycle repeated and that the conjunctions would occur in the constellations on the ecliptic at equal intervals set 120-degrees or four zodiacal constellations apart. The repeating pattern is known as a "trigon"

Although today most people view the planetary patterns as a result of constant, stable orbits of the planets, years ago, this trigon had an ominous portent. Some were fearful until they saw that nothing terrible happened they could connect to the celestial situation. The only interest in astrology at Astra's Stargate is in the historical context for astronomy. Indeed, as witnessed by Galileo, the Church looked down on any attempt to defame the currently accepted (by the Church) science of the day.

Instead of the usual observing article, this month we have a little history as well. I'd like to talk about the 16th century astronomer, Johannes Kepler. As a young man, Kepler was deeply religious and wanted to be a clergyman. He found himself working at the Evangelical Seminar in Graz, Austria, where he taught mathematics as well as Latin and other classes. In addition, he wrote an astrological calendar and made some predictions that seemed to come true--winning him some astrological fame. But Kepler was fascinated by the astronomical questions of the day, pondering the distances and velocities of planets.

To illustrate the great conjunction to his mathematics students, Kepler drew the trigon. Carefully placing the points of the great conjunction in circle marked by the zodiacal constellations, he drew the beginning of the next trigon by continuing the line that ended the first. Going around 40 times, he showed that the cycle would start over after 800 years. The resulting image has been reproduced here. Kepler realized that the lines of the trigons formed inner and outer circles that described the difference between the orbits of Jupiter and Saturn. Needless to say, this excited him into testing other planets that might fit neatly into geometric figures. This lead to Kepler writing his first book, "Mysterium Cosmographicum" or The Cosmographic Mystery. This book helped to reinforce the ideas of Copernicus, with a sun-centered universe. (Today we know it really meant the solar system.)

Although Kepler failed to find simple keys to planetary orbits, it is very possible that this exercise fired his imagination and inspired him to continue his studies until he eventually developed his 3 laws of planetary motion. Kepler's interest in the planets led him to the greatest observational astronomer of his time, Tycho Brahe. Tycho was a Danish nobleman who made meticulous observations with special equipment that he had constructed to his specifications. Kepler worked with him at his observatory in Prague, until Tycho's untimely death in 1601. Kepler studied Tycho's observations of Mars, the planet Tycho had assigned to him originally. It was through the study of Mars' orbit that Kepler finally realized that the planets' orbits were elipses. Once he figured that out, he was able to understand how planets move faster and slower in their orbits, finally breaking through and starting astronomers on the correct path to decipher the mechanics of the solar system.

Mars Stars

From the great conjunction of Jupiter and Saturn, we turn to Mars as Earth comes ever closer to overtaking the red planet in its orbit in October of this year. Don't miss out this apparition because the next opposition of Mars the red planet will be farther away from Earth. Because of the 15.2-year cycle, the next opposition begins the series of aphelic oppositions when the red planet is farther away. For the December 08, 2022 opposition, the disk of Mars will be only 17.2” (arc-seconds) - - smaller than Mars' disk at the begining of September this year. For more information on oppositions of Mars, check out Astra's Mars Oppositions and the Mars Opposition 2020 pages.

The planet Mars starts out in September a bit shy of 19" and finishes over 21". The surface goes from 92% illumination and -1.8 mag to 99% illuminated and -2.5 magnitude. At closest approach on October 6, 2020, Mars will be 38,568,243 miles or 62,069,571 km away from Earth. The actual moment of opposition will occur at 2320 UT on October 13, 2020.

--See You Under the Stars!
Astra for Astra's Almanac