When looking at the southern sky this month, the Milky Way dominates the view. Along with it, the two largest planets in our solar system are easily seen in the night sky after sunset and are high in the sky.
Both Jupiter and Saturn are best viewed with a telescope.
Jupiter was named after the Roman god of the same name, the god of thunder, lightning, and storms. Greeks named it after their god Zeus. Because of its 12-year journey around the sun, the ancient astronomers divided the path of Jupiter into the 12 zodiacal constellations.
Galileo was the first person who recorded a view of Jupiter thru a telescope. He observed that there were four small star-like objects very close to the planet. When viewing Jupiter over a period of several nights, he observed that the small star-like objects revolved around the planet. This view was in opposition to the belief of that time that all objects revolved around Earth. Galileo’s observation was one of the first proofs that the solar system was heliocentric (sun centered) rather than geocentric (earth centered).
Today the four primary moons of Jupiter are known as the Galilean moons. Their names are Io, Europa, Ganymede, and Callisto.
To the ancient world, Saturn was the god of agriculture. Galileo also viewed Saturn with his telescope, but his observation troubled him. When he viewed Saturn, he observed two moons on either side of Saturn. When viewing Saturn several months later, the moons were gone. Not knowing what he viewed, Galileo didn’t report his observations.
It wasn’t until Christiaan Huygens viewed Saturn thru a better telescope that the ring system was visible. Even the smallest telescope will show the intricate ring system. With even larger telescopes, more rings are able to be viewed. Several moons are also visible orbiting the planet. Titan, the largest moon of Saturn, has a methane atmosphere.
The ring systems of Saturn are 66 feet in thickness and about 70,000 miles in diameter. They are made up of countless small dust particles and small ice crystals. There are thousands of ring systems orbiting the planet.
When the Voyager 1 space probe was sent to Jupiter in the 1990s, it discovered a very thin and faint ring system around the planet. Voyager 2 discovered rings around Uranus and Neptune.
Autumnal equinox will occur on Sept. 23. This marks the first day of autumn.
Venus and Mercury will return to the evening skies at the end of the month. They will be extremely low on the western horizon on the evening of Sept. 30.
The next meeting of the Springfield Astronomical Society will be Sept. 24. It will be at the Library Center at 4653 S. Campbell Ave., Springfield. Starting time is 7 p.m. Our website is http://www.springfieldastronomy.org.