This is the Dudley Observatory Skywatch Line for Wednesday, July 11th, and Thursday, July 12th, written by Louis Suarato.
The 2% illuminated, waning crescent Moon sets at 7:14 p.m. Wednesday. The Moon will reach its New phase at 10:48 p.m. Thursday. Lunar perigee, the Moon’s closest distance to Earth during this lunar cycle, occurs at 4:28 a..m. Friday. The combination of lunar perigee so closely following the New Moon will cause higher, and lower, than normal tides. This difference in tides is caused by the Moon’s close proximity, and alignment with the Sun, gravitationally causing the oceans to bulge higher than average on the Moon’s side of the Earth. As the Earth rotates under the bulge of water, tides rise, and as that same area rotates away from the bulge, tides subside.
Five planets are easily visible in the night sky. Look for Mercury low over the northwestern horizon before it sets at 9:35 p..m.. Mercury is 43% illuminated, and will reach its greatest eastern elongation, 26 degrees from the Sun, on Thursday. Venus will be 12 degrees over the western horizon as Mercury is setting. A telescopic view of -4.10 magnitude Venus will reveal it is 66% illuminated. Look for -2.24 magnitude Jupiter 30 degrees over the south-southwestern horizon. Thursday night, Jupiter’s Moon Io, and its shadow, will cross the face of the planet from 10:35 p.m. until 11:34 p.m., when Io’s transit ends. Saturn, just past its opposition, and still 100% illuminated will be in the sky all night. Look for the ringed planet in the constellation Sagittarius, above the south-southeastern horizon before midnight. Last up is 98 % illuminated, -2.49 magnitude Mars. Mars rises in Capricornus at 10:00 p.m., and sets after sunrise.
On July 11, 1801, astronomer Jean-Louis Pons discovered his first comet. During his lifetime, Pons discovered, or co-discovered 37 comets, more than any other person. The July 11,1801 discovery was shared with Charles Messier, who reported seeing the comet the next day. Pons’ first discovery was Messier’s last. Pons continued to discover comets almost every year until his sight failed in 1827. Comet C/2017 S3 (PANSTARRS) suddenly brightened recently. Observers reported the green comet exploded from 12th magnitude to 9thmagnitude and expanded in size to almost double the width of Jupiter. This visitor from the Oort Cloud was expected to be seen with the naked eye in August, but is currently only visible through binoculars and telescopes. You can find the location of Comet C/2017 S3 (PANSTARRS) for any given day using the Heavens-above website. https://www.heavens-above.com/comet.aspx?cid=C%2F2017%20S3&