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The Sky This Week, 2019 June 11 - 18

Mpre places on the Moon to visit.
Region of Mare Humorum, imaged with a Celestron 9.25-inch Schmidt-Cassegrain telescope from Alexandria, Virginia
Region of Mare Humorum, imaged 2018 May 26 with a Celestron 9.25-inch Schmidt-Cassegrain telescope
and a ZWO ASI224MC imager from Mollusk, Virginia. The prominent crater Gassendi is on the terminator right of center.
The elongated crater Schiller is to the left.

The Moon waxes in the evening sky, washing out the stars of late spring as she heads toward the southern reaches of the ecliptic.  Full Moon occurs on the 17th at 4:31 am Eastern Daylight Time.  June’s Full Moon is popularly known as the Rose Moon, Strawberry Moon, Mead Moon, or Honey Moon.  All of these names reflect the warm tint that the Moon takes on for observers in northern climes; as the Moon skirts the southern horizon her light passes through more air along our line of sight.  Air molecules selectively scatter blue light, which, in turn, makes Luna appear a bit more red.  You’ll find the Moon about seven degrees north of the bright star Antares on the evening of the 15th.  On the following night she will be just to the east of bright Jupiter.

This week we see the earliest sunrises of the year.  In the Washington, DC area Old Sol crests the horizon at 5:42 am EDT each morning until the 17th, when he gradually begins to rise a dad later.  Our latest sunsets will occur for a few days before and after the 28th.  In between, the summer solstice will fall on June 21st.  From now until the end of the month Washingtonians will experience over 14 hours and 50 minutes of daylight, and the Sun will cross the meridian just 15 degrees south of the zenith, so don’t forget your sunscreen before venturing out at mid-day!

The short nights are once again dominated by the bright Moon, and, as was the case last week, you don’t have to stay up late to enjoy views of her battered surface.  As the week opens the terminator line bisects the largest impact basin on the lunar surface, the so-called Mare Imbrium, or Sea of Showers.  This vast basin measures some 1250 kilometers (750 miles) in diameter and formed from the impact of a large asteroid about 3.8 billion years ago.  Molten lava from the young Moon’s interior flooded the huge remnant crater, giving it a relatively smooth, dark surface pock-marked with smaller, more recent impacts.  As the week progresses the terminator will reveal more of the giant feature.  On the evening of the 13th look for a partially-filled crater on the basin’s northern rim that forms a feature known as the Sinus Iridum, or Bay of Rainbows.  Follow the terminator to the south and you’ll run into another lava-filled basin, Mare Humorum, the Sea of Moisture.  This is another asteroid blemish that pre-dates the Imbrium impact by about 100 million years.  It is about 380 kilometers (230 miles) across.  Its northern rim is dominated by one of my favorite lunar features, the crater Gassendi.  This formation has a very prominent central peak, and its floor is criss-crossed by a number of linear furrows known as rilles.  On the opposite side of Mare Humorum are a number of other prominent craters, many of which have been flooded by lavas that filled the Humorum basin after its formation.  Continuing to the south along the terminator, we now encounter the lunar “highlands” which preserve the Moon’s early history of intense bombardment during its formation over 4 billion years ago.  Here you will notice a very unusual crater, Schiller.  This feature is extremely elongated and probably resulted from an asteroid that crashed at a very shallow angle.

There is some interesting activity happening in the western sky during the twilight hours.  You’ll need a clear sky and a flat horizon to watch Mercury close in on the ruddy glow of Mars as the week progresses.  On the evening of the 18th the two objects will be just one-quarter of a degree apart and 10 degrees above the horizon about 45 minutes after sunset.  Binoculars should help you track down the pair, of which Mercury will be the brighter member.

Jupiter reached opposition on the 10th, and on the 12th the giant planet and Earth are closest together for the current apparition, with a mere 641 million kilometers (398 million miles) of space between them.  Old Jove now dominates the southern sky from a perch above the distinctive constellation of Scorpius.  Once the Moon leaves the scene next week you’ll find Jupiter hanging in front of one of the dense star clouds of the Milky Way.

You’ll find golden Saturn tracking behind Jupiter during the late-night hours.  While he isn’t as bright as Old Jove, the ringed planet still outshines everything else in the area.  Saturn follows the “teapot” asterism of Sagittarius into the night, just east of the bright core of the summertime Milky Way.

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