This is the Dudley Observatory Skywatch Line for Wednesday, September 16th and Thursday, September 17th written by Louis Suarato
The 12% illuminated, waxing crescent Moon can be seen low over the west-southwestern horizon after sunset before setting at 8:30 p.m. Wednesday evening. This is a good time to see “Earthshine” on the Moon. Earthshine is sunlight reflecting from the Earth onto the Moon’s shadowed surface creating a faint glow. It was Leonardo Da Vinci who concluded that Earthshine was created by the Earth’s reflected sunlight. Da Vinci was wrong about sunlight reflecting off the Earth’s oceans onto the Moon’s oceans, since Earthshine occurs when sunlight reflects off the Earth’s clouds, and, of course, the Moon doesn’t have oceans. But given Da Vinci’s perceptions occurred during the early 1500’s, years before even Copernicus’ heliocentric theories were published, it was an amazing discovery. Earthshine, also known as “The Da VInci Glow”, is best viewed 1 to 5 days before and after the New Moon.
You can find Saturn in the constellation Libra, to the upper left of the crescent Moon. Look about 15 degrees over the southwestern horizon. It was September 17, 1789 when William Herschel discovered Saturn’s moon Mimas. Mimas is the 7th largest moon of Saturn, and the 20th largest in the solar system. Mimas’ most outstanding feature is a gigantic crater known as Herschel. This crater measures one-third of Mimas’ 242 mile diameter.
The pre-dawn hours welcome the arrival of three planets. Venus is the first to rise at 3:40 a.m. Thursday, followed by Mars at 4:08 and Jupiter at 5:15. Look over the eastern horizon for all three planets. Continue to follow these planets as they draw closer during October.
The Dudley Observatory will host two events this week. The first is a lecture and star party at the Octagonal Barn in Delanson, NY on Friday, September 18th, beginning at 7 pm. The lecture will be given by Dudley Observatory’s archivist Josh Hauck on “A Scientific Sweatshop: The Industrialization of American Science and the Women of Dudley Observatory”. The Dudley Observatory will also be hosting “International Observe the Moon Night” at MiSci in Schenectady, beginning at 7 pm on Saturday, September 19th. More information about these events can be found at www.dudleyobservatory.org.
The Albany Area Amateur Astronomers will be hosting a Star Watch on Friday, September 18th at Grafton Lake State Park. If the Friday event is cancelled, it will be held Saturday night.