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The Sky This Week, 2018 July 3 - 10

The endless cosmic chase
Jupiter (above tree to left), Scorpius (just left of lens flare from Moon)
and Saturn, (just above peak at left), 2018 June 21

Imaged in Desolation Canyon, Utah with a Canon EOS Rebel T2i DSLR.

The Moon wanes in the morning sky this week, making her way through the rising stars of the autumn sky.  Last Quarter occurs on the 6th at 3:51 am Eastern Daylight Time.  She spends most of the week among the faint stars that define the obscure constellations of Aquarius, Pisces, and Aires.  By the week’s end she closes in on the bright star Aldebaran in the constellation of Taurus, the Bull.  If you rise before dawn on the morning of the 10th, you’ll find Luna’s slender crescent just above Aldebaran in the gathering morning twilight.

The short nights of high summer mean that we don’t achieve full astronomical darkness until around 10:30 pm.  With the waning Moon you have increasing time to enjoy the sights of the season’s sky.  One of my favorite sights in the summer sky is the constellation Scorpius, which crosses the meridian to the south at around midnight at this time of the year.  Scorpius is one of the few constellations that resembles its namesake, and depictions of its distinctive shape date back to very ancient times.  The brightest star in the group, Antares, is a “red supergiant” star, a highly evolved massive star that is nearing the end of its lifetime.  It marks the scorpion’s heart.  The nuclear fusion that powers it originates in shells around its core, which is accumulating iron as an end fission product.   This causes the star to swell to enormous size; if it were located at the Sun’s position in our solar system its outer layers would encompass the orbit of Mars!  Many of the other stars in Scorpius belong to an association of hot blue stars.  This is similar to the winter constellation of Orion, the Hunter.  Orion also contains a red supergiant star, Betelgeuse, which is very similar to Antares.  Interestingly, Betelgeuse rises at around the same time that Antares sets, and for a good reason.  In mythology, one of the legends accompanying Orion concerns his boast that he could defeat any animal on the Earth.  To prove him wrong, and to put him in his mortal place, the goddess Juno sent a lowly scorpion to do him in.  He was eventually granted a place among the stars, but his place was carefully selected so that he would never encounter the scorpion on the same night.  Scorpius’ most notable feature is its tail, which just clears the southern horizon when it culminates.  It dips down toward the horizon like a giant fish-hook, and ends in two closely-spaced stars that mark the scorpion’s deadly stinger.  This asterism is one of the most important star patterns to Polynesians, who see it as “Maui’s Fish-hook”, the implement that their creator god used to pull their islands up from the bottom of the sea.

Venus is now beginning to lose ground on the encroaching Sun as she slides eastward along the ecliptic.  At the same time she is drifting southward with respect to the western horizon.  This week she closes in on the bright star Regulus in Leo, the Lion.  She passes just one degree north of the star on the evening of the 9th, providing a very nice binocular view.

Jupiter stands above the southern horizon as evening twilight fades.  You’ll want to get the telescope on him during this time since that’s when he’ll be at his highest point in our sky.  He reaches the second stationary point in the current apparition on the night of the 10th.  He will slowly resume direct eastward motion against the stars for the rest of the summer, passing just north of the star Zubenelgenubi in mid-August.

Saturn is easily seen in the southeastern sky as evening twilight fades and should be high enough to get a good view in the telescope by 10:00 pm.  Distortion from Earth’s atmosphere will hamper viewing fine details in the planet’s rings, but you should have no trouble spotting the rings themselves.  Oddly enough, hot, sultry July nights can often offer the best viewing conditions if you’re looking for small-scale features.

Mars is fast approaching opposition, which will occur on the 27th.  This will be the best apparition of the red planet since 1988, and he won’t approach us at a comparable distance until 2035.  His disc is now over 20 arcseconds across (about half the apparent diameter of Jupiter) and will continue to grow until opposition.  That said, he is at a very low declination, and a planet-wide dust storm is raging, hiding the planet’s elusive surface details.  We don’t know how long the storm will last, but hopefully it will clear out before Mars recedes from us in the fall.

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