The Sky This Week
U.S. Naval Observatory's Weekly Blog

Into the Mouth of the Southern Fish

by Geoff Chester, USNO Public Affairs
09 November 2021

Jupiter and three moons, imaged 2021 November 9, 01:05 UT
with the USNO's 30.5-cm (12-inch) f/15 Clark/Saegmüller refractor,
and a ZWO Optical ASI183MC CMOS color imager.

The Moon waxes in the evening sky this week, climbing northward along the ecliptic as she negotiates a path through the Zodiac’s “water constellations”.  First Quarter occurs on the 11th at 7:46 am Eastern Standard Time.  Look for the crescent Moon near the planet Saturn on the evening of the 10th.  She passes southeast of bright Jupiter on the following evening.

Our first full week back on Standard Time finds the early evening hosting the dim constellations of fall.  Urban stargazers may wonder where all of the bright stars have gone if they look southward at around 7:00 pm local time.  The stars are there, they are just quite faint.  The three large Zodiacal constellations of Capricornus, Aquarius, and Pisces have no stars brighter than third magnitude, making them difficult to see from the centers of large cities and suburbs.  However, there is one lonesome star that skirts the southern horizon as the early evening hours roll by.  That star is Fomalhaut, the brightest star in the constellation of Pisces Austrinus, the Southern Fish.  Fomalhaut is the 20th-brightest star in the sky, slightly brighter than Deneb in Cygnus.  Located about 25 light-years from Earth, Fomalhaut is close enough to us to show a broad disc of dust circling its equator.  This feature is considered to be a proto-planetary disc since Fomalhaut is a comparatively young star, perhaps 400 million years old.  The disc was first imaged by the Hubble Space Telescope, and in 2008 astronomers announced that an apparent planet had been spotted in the Hubble images.  The exact nature of this supposed planet is still controversial, but it may be a world caught in its early stages of formation.

By 8:30 pm the brightest of autumn’s constellations, Pegasus, is crossing the meridian high in the south.  This sprawling constellation is dominated by four stars that form a distinctive square, so many refer to it as the Great Square.  The star at the upper-left corner of the square is marked by its brightest star, Alpheratz, which is “shared” with the constellation of Andromeda.  The latter constellation sweeps northeast of Pegasus as two diverging chains of stars, the brighter one pointing toward Perseus while the fainter one tails off toward Cassiopeia.  All of these constellations are related in mythology, each a part of a grand story of vanity, vengeance, innocence, and heroism.
 
By midnight the bright stars of the Great Winter Circle have cleared the eastern horizon, seemingly filling the eastern skies with dozens of bright stars.  The circle surrounds the bright stars of Orion, the Hunter, which is arguably the most prominent constellation in the sky.  Because of its location straddling the celestial equator, Orion is visible in whole or in part from everywhere on the Earth, and his outline figures prominently in the sky lore of virtually every culture that has left records of their astronomical and astrological observations throughout history.  

The spate of crisp, clear night of late gave many of us a grand view of the dazzling planet Venus and the thin waxing crescent Moon.  Venus has begun to move northward along the ecliptic as she passes through the stars of Sagittarius this week.  She is hard to miss in the evening twilight sky, and over the course of the next few weeks she will gain a bit more elevation from the southwest horizon before she begins her year-ending plunge toward the Sun.

Saturn languishes among the dim stars of the constellation Capricornus, the Sea-Goat, and may be found just west of the meridian an hour after sunset.  Due to his southerly declination you only have a couple of hours to view him in steady air through the telescope, but it’s well worth the effort to do so.  I never tire of looking at his amazing rings.

Jupiter follows closely on Saturn’s heels.  He enjoys a somewhat higher position along the ecliptic, so viewing conditions for him last longer into the night.  Of all the planets visible in small telescopes, Jupiter sports the largest apparent disc.  A good three-inch telescope will reveal Old Jove’s dark equatorial cloud belts, and a four-inch instrument will show the enigmatic Great Red Spot on nights of steady air.  If you have an 8-inch instrument you can spend hours examining finer details in the planet’s clouds as they slowly rotate across the cream-white disc.
 
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