This is Dudley Observatory’s Skywatch Line for Friday, June 21 through Sunday, June 23, written by Sam Salem.
On Friday, Sun rises at 5:17am and sets at 8:38pm; the waning gibbous Moon rises at 11:52pm and sets at 9:11am.
The solstice arrives at 11:54am on Friday. The Sun is farthest north for the year and begins its six-month return southward. This is the year’s longest day and shortest night in the northern hemisphere. It’s also the day when the midday Sun passes the closest it can to being straight overhead and your shadow becomes is the shortest it can ever be. For stargazers, from this date onward, nights will start getting longer. If you have a good west-northwest horizon, mark very precisely where the Sun sets. In a few days you should be able to detect that it’s starting to set a little south of that point.
Evening twilight presents a trio of planets. Low in the west sit Mars and Mercury, which are positioned close together all week. Jupiter, at magnitude –2.6, sits in the east, just one week after opposition. Jupiter now culminates around midnight, when it sits due south and is highest. On Friday, Jupiter’s Great Red Spot should transit the planet’s central meridian, the line from pole to pole down the center of the planet’s disk, around 1:21am. Meanwhile Europa, the smallest of Jupiter’s Galilean moons, crosses the planet’s disk on Friday night from 11:32pm to 1:57am, followed closely by its tiny black shadow from 12:04 to 2:32am. Jupiter sets around 4:30am.
Saturn, shining at magnitude 0.2, rises a bit before 10:00pm and reaches the meridian just before 2:30am. Venus, at magnitude –3.8, clears the east-northeast horizon about one hour ahead of sunrise.
Mid. to late June is an excellent time to look for the planet Mercury in your western sky after sunset. On Sunday, Mercury reaches a milestone as it swings out to its greatest elongation of 25 degrees east of the setting Sun. Mercury, the innermost planet of the solar system, is often lost in the Sun’s glare. The best chance of catching Mercury after sunset is generally around the time of Mercury’s greatest eastern elongation. That’s because Mercury is now setting a maximum while after sunset. Mercury now stays out better than 1 1/2 hours after the Sun. To spot Mercury, find an unobstructed horizon in the direction of sunset. Then, starting an hour or so after sundown, watch for Mercury to pop out rather low in the western sky and near the sunset point on the horizon.
Neptune is stationary on Saturday. Neptune, at magnitude 7.9, sits in constellation Aquarius. It is well up in the southeast just before dawn begins, lower right of the Great Square of Pegasus.
Leo the Lion is a constellation of late winter and spring. But it has not gone yet. As twilight ends, look low due west for Leo’s brightest star Regulus, now lowest star the forefoot of the Lion stick figure. The Sickle of Leo extends upper right from Regulus. The rest of the Lion’s constellation figure extends for almost three fist-widths to the upper left, to his tail star Denebola, the highest.