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The Sky This Week, 2020 June 30 - July 7

A busy Independence Day.
The Moon, imaged 2020 June 30, 02:30 UT from Alexandria, Virginia.
The Moon, imaged 2020 June 30, 02:30 UT from Alexandria, Virginia
28 subframe mosaic made with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor,
2X TeleVue "Big Barlow" lens, and a ZWO ASI224MC imager.

The Moon brightens the evening sky this week, providing a fitting backdrop to Independence Day fireworks.  Full Moon occurs on July 5th at 12:44 am Eastern Daylight Time.  July’s Full Moon is popularly known as the Hay Moon, Elk Moon, Buck Moon, or Thunder Moon.  The latter seems particularly appropriate for the sweltering afternoons we experience here in Washington, but hopefully the showers will hold off for this year’s observance.  This Full Moon also happens to coincide with a penumbral lunar eclipse, which takes place between 11:07 pm EDT on the 4th and 1:52 am EDT on the 5th.  This will be a very minimal eclipse, as only the northern third of Luna’s disc will pass through Earth’s penumbral shadow.  You may notice a very slight darkening near the Moon’s northern limb, but the effect will be very subtle, and most people won’t notice anything very different in Luna’s appearance.  Our next view of a lunar eclipse will be on November 19th, 2021, when 97 percent of the Moon’s disc will be covered by the Earth’s umbral shadow.  The Thunder Moon will be accompanied by the planets Jupiter and Saturn on the evening of the 4th, while on the following night she will form the southern apex of a triangle with the two gas giants.

The time of sunset gradually starts to inch earlier this week, but early risers may have already noticed that the time of sunrise is now about five minutes later than it was in mid-June.  I have noticed this because for the past several weeks a shaft of sunlight comes through a gap in my blinds to shine directly on my face each morning at around 6:30 am.  Now it’s running five minutes later, and in another week I’ll once again need to set the harsh ring of the morning alarm.  Fortunately there is still plenty of time to enjoy the day, but the pace of shortening daylight will soon begin to gather momentum.

July 4th also marks the date of Earth’s aphelion, its farthest distance from the Sun.  This will occur at 7:35 am EDT, when our fair planet will be some 152.1 million kilometers (94.5 million miles) from Old Sol.  Earth’s orbit is very nearly circular, so six months from now we’ll reach perihelion, only three percent closer to the Sun than we are now.

With a bright Moon and fireworks filling the sky, only the brightest of stars will shine through the hazy summer skies.  If you look high overhead as twilight fades you will see the rose-tinted glow of Arcturus, the brightest star in the northern sky.  High in the northeast you will see a star of similar brightness but sporting a subtle blue tint.  This is Vega, the brightest star of the asterism known as the Summer Triangle.  Somewhat lower in the northeast is the dimmest of the three Triangle stars, Deneb.  The third star in the triangle is Altair, which climbs higher in the east as the evening passes.  Arcturus, Vega, and Altair are relatively close neighbors to the solar system, lying 37, 25, and 17 light-years away, respectively.  Deneb, however, is much farther afield.  The distance to this star is not well known, but it is likely in the range of 1500 to 2000 light years!  That means that the light we see from Deneb tonight began its journey toward us at around the time of the fall of the Roman empire!  If we could somehow drag Deneb to the distance of Altair, it would shine with the equivalent light of the first quarter Moon, and night would be very different when it is above the horizon.

Giant Jupiter is inching closer to opposition as July opens, rising shortly after 9:00 pm as the week ends.  Old Jove is slowly moving westward toward the “teapot” asterism of Sagittarius.  Binoculars will show him in a rich field of faint stars.

Saturn rises about 20 minutes after Jupiter, and the two planets will spend the rest of the summer in close proximity.  Saturn’s rings are still tipped over 20 degrees to our line of sight, so the view of this distant world through the telescope should provide lots of time for enjoyment.

Mars is wending his way eastward through the faint stars of Pisces and remains best placed for viewing in the pre-dawn sky.  The red planet is gradually brightening and should be easy to spot thanks to his ruddy tint.  July will be a busy month for Mars aficionados as three space probes will be dispatched toward it, arriving in early 2021.