Skywatch Line for Friday, September 13, through Sunday, September 15, 2019

This is Dudley Observatory’s Skywatch Line for Friday, September 13, through Sunday, September 15, written by Sam Salem.

On Friday, Sun rises at 6:33am and sets at 7:10pm; the full Moon rises at 7:23pm and sets at 5:45am. Full Harvest Moon occurs at 11:33pm on Friday. This September full Moon is the closest full Moon to the September autumn equinox, hence the name “Harvest Moon”. This full Moon also happens to be the smallest of this year. On Friday, watch for 1st-magnitude Fomalhaut rising to the Moon’s lower right, by about two fists at arm’s length. After dark on Saturday, look upper-left of the Moon for the Great Square of Pegasus balancing on one corner. The Square is made of 2nd- and 3rd-magnitude stars. By the end of twilight the bright Moon, a day past full, has risen to shine low in the east. Look a couple of fists to its upper left for the Great Square of Pegasus tipped onto one corner. The Square’s lower left side points diagonally down at the Moon.

Jupiter, at magnitude -2.2, is found between the feet of constellation Ophiuchus. It sits roughly 20 degrees above the south-southwest horizon as twilight fades away. Get your scope on it early before it sinks lower into even poorer seeing. Orange star Antares, in constellation Scorpius, looks much fainter at magnitude +1.0. It twinkles 7½ degrees to Jupiter’s lower right. In a telescope, Jupiter is only 38 arc-seconds wide and shrinking. Saturn, at magnitude 0.4, culminates around 8:30pm with an altitude of roughly 23 degrees. Saturn is the steady, pale yellowish “star” in the south-southeast during and after dusk. Saturn sits 28 degrees left, or upper left, of Jupiter. Below Saturn is the handle of the Sagittarius Teapot. Jupiter sets around 11:00pm and Saturn sets around 1:00am.

Hunt down planet Neptune this weekend. Neptune is currently at its brightest, though that stat doesn’t change much throughout the year. Neptune was at opposition this week the night of September 9th and is passing 4th-magnitude Phi Aquarii. Right now, Neptune is at magnitude 7.8. When the planet is less favorably positioned, it dips an imperceptible 0.2 magnitude, to 8.0. Neptune is bright enough to be viewed in small telescopes, even when a full Moon is present. The star and planet are 12 arc-minutes, or 0.2 degrees, apart on Friday. They’re well up in the southeast by about 10:00pm and are highest in the south soon after midnight. You can start your search much earlier than that. The planet is making its way through the big, dim constellation Aquarius. Locating Neptune this weekend is not too difficult since it’s found just 0.2 degree west-southwest of 4.2-magnitude star Phi (φ) Aquarii. Center Phi (φ) Aquarii in your scope, crank up the magnification, and Neptune should be obvious as the brightest object near the star. In a telescope, Neptune is merely a blue-green point of light, just 2.3 arc-seconds in diameter. It appears only slightly bigger than Jupiter’s largest moon, Ganymede, which is 1.6 arc-seconds wide. You’ll have to use high magnification to resolve that pale pinpoint into a tiny disk.

Scientists have extracted a unique geologic record when a city-sized asteroid smashed into the planet 65 million years ago wiping out the dinosaurs and three-quarters of all other life. Their analysis of these new rock samples from the Chicxulub crater, in Mexico, was made public on Monday. The analysis reveals a parfait of debris deposited in layers almost minute-by-minute at the heart of the impact during the first day of a global catastrophe. It records traces of the explosive melting, massive earthquakes, tsunamis, landslides and wildfires as the immense asteroid blasted a hole 100 miles wide and 12 miles deep. Drilling into the seafloor off Mexico, the scientists worked aboard a drilling ship anchored offshore from the Mexican port of Progreso. In 2016, they drilled into the crater’s inner rim for the first time, buried in the seafloor under about 1,500 feet of limestone deposited in the millions of years since the impact.

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