This is the Skywatch Line for Monday and Tuesday, May 18th and 19th, written by Joe Slomka.
The Sun sets at 8:15 PM; night falls at 10:17. Dawn begins at 3:25 AM and ends with the Sun rising at 5:29.
The Moon is not seen on both nights. Tuesday’s 26-day-old Moon rises at 4:17 AM, is 10% illuminated, 6° high and sets at 5:15 PM. Wednesday’ Moon rises at 4:40 AM, is 6% lit and sets at 6:16 PM.
Two evening planets share Taurus. Venus is the brightest planet in the sky. It blazes with minus 4th magnitude, appears as a thin crescent, 8% lit and 14° high and sets at 10:17 PM. Mercury now appears 7° below Venus, appearing 77% lit, 7° altitude, glaring with minus zero magnitude and setting at 9:36 PM.
The pre-dawn sky is where the action is. Sagittarius houses Jupiter and Pluto. Dwarf planet Pluto actually rises first at 12:25 AM, shining with 14th magnitude, appearing less the one-arc second diameter and 22° high. Jupiter rises 4 minutes later, glowing with minus 2nd magnitude and 43 arc-seconds wide.
Saturn is the second major planet to rise, in Capricornus, at 12:44 AM, shining with zero magnitude and 17 arc-seconds breadth. Mars is socially distancing itself from the rest. It rises, in Aquarius, at 2:20 AM, appears a bit smaller than Saturn but almost 9 arc-seconds and 24° high. The Red Planet shares Aquarius with Neptune, which rises at 2:54 AM, 8th magnitude bright, 21° high and a small 2 arc-seconds. Another Dwarf planet, Ceres, also in Aquarius, rises at 2:56 AM below Mars is 97% lit, 17° high and shines with 8th magnitude, making it visible in 6-inch telescopes.
If that wasn’t enough, we have an interloper in our pre-sunrise sky. Comet Swan (C/2020 F8) is making a low appearance in the north-east sky. The comet was discovered by Australian amateur astronomer Michael Matiazzo on March 25th through the SWAN telescope. The comet is very bright and obvious in the southern hemisphere sky, but now it rises at 2:43 AM in the constellation Triangulum on Tuesday morning, and Perseus on Wednesday. It shines with 5th magnitude and is 8° high at 4 AM and 12° at 4:30. Wednesday finds it one-half degree away from the variable star Algol,
Putting it within the same finder scope field. Comet Swan also has an evening apparition from about May 23rd to June 10th for mid-northern observers.
Saturn is the showpiece of any star party. But, Saturn is not the only planet that has rings. Jupiter, Uranus and Neptune were discovered to display rings by space-borne probes. A new member joins the club. In 2014, the European Space Organization (ESO) announced that Chariklo, an asteroid, possesses rings. This was an accidental finding. The ESO had several observatories study Chariklo as it occulted, or eclipsed, a star – to determine its size and shape. When they studied the results, the star was occulted three times. First it flickered; secondly the asteroid blacked it out; thirdly, it flickered again. Astronomers deduced that rings surrounding Chariklo caused the flickering. Chariklo is a Centaur asteroid: it is rock, enclosed by a fuzzy comet-like halo of gas. The occultation revealed that it is the largest Centaur – 160 miles in diameter.