This is Dudley Observatory’s Skywatch Line for Friday, June 22 through Sunday, June 24, written by Sam Salem.
On Friday, the Sun rises at 5:18am and sets at 8:38pm; the waxing gibbous Moon rises at 3:17pm and sets at 2:10am. On Saturday evening, the waxing gibbous Moon and Jupiter are separated by less than 4 degrees. On Sunday, the Moon shines near the three stars forming the head, or the crown, of the Scorpion in the constellation Scorpius, in the south-southeastern sky. Use the bright star Antares to guide you to the Crown of the Scorpion when the Moon drops out the evening sky. The Crown star names are Graffias, Dschubba, and Pi Scorpii.
Mercury doesn’t stay very far from the glare of the Sun. Chances of observing Mercury this weekend are decent if you have an unobstructed west-northwest horizon. Use binoculars, or a small scope. Mercuryshines at magnitude –0.7 and sets roughly one hour after the Sun. Mercury will continue to gain altitude in the coming weeks. However, it will be somewhat dimmer. Venus and Jupiter are both well placed at dusk. Venus shines in the west shortly after sunset. Jupiter, sits due south at around 10pm. Mars, at magnitude –1.8, rises shortly before midnight. This week Mars’ disk equals 18..6 arc seconds, which is the maximum size it attained during the most recent opposition in 2016. Observe Mars when it’s highest around 4am. Mars may look like a featureless, fuzzy peach, in a telescope depending on how a dust storm now unfolding in the planet’s southern hemisphere. Saturn, glowing at magnitude 0.1, appears low in the southeast as dusk deepens. It reaches near the meridian around 2am.
Spot the brightest asteroid, Vesta, this weekend using binoculars or a small telescope. Shining at magnitude 5.4, you might have a chance to spot Vesta even though this weekend features a waxing gibbous Moon. Vesta currently resides in northern Sagittariusand is positioned about two degrees southwest of open cluster M23. The asteroid was first sighted by Heinrich Wilhelm Matthias Olbers in 1807. Itmeasures roughly 525 kilometres across, which makes it the second biggest asteroid-belt object, after Ceres. The title of largest asteroid now belongs to Vesta after Ceres has been reclassified as a dwarf planet. Use a telescope to spot the asteroid locatedvery close to the 9.3-magnitude globular cluster NGC6440. Make a field sketch and note Vesta’slocation relative to its surrounds. A night or two later, go out and look again when Vesta’s position has changed. Its proximity to the globular and open cluster will make the asteroid’s motion easy to detect.
Friday marks the 40th anniversary of the discovery of the 1st moon of Pluto, Charon, by Christy and Harrington. In 1978, evidence of the first moon of Pluto was discovered by astronomer James W. Christy, of the Naval Observatory in Arizona. Christyobtained a photograph of Pluto that showed the orbitto be distinctly elongated. The elongations appeared to change position with respect to the stars over time. The elongation proved to be caused by a previously unknown moon orbiting Pluto at a distance of about 12,100 miles with a period of 6.4 days. The moon was named Charon, after the ferryman in Greek mythology who took the souls of the dead across the River Styx to Pluto’s underworld.