Sunday Brings a Punymoon and Rare Double Spots on Jupiter, Mercury at Max Visibility!
The Moon and Planets
The moon will occupy the evening sky worldwide during this entire week, while it transitions from a “puny” full moon tonight to last quarter next Monday. Meanwhile, the Earth’s neighboring planets, Venus and Mars, will both increase in visibility as they move farther from the evening and morning sun, respectively. And Mercury will reach peak visibility, too. Here are your Skylights!
Today (Sunday) at 5:09 pm EDT, the full moon of October, traditionally called the Hunter’s Moon, Blood Moon, or Sanguine Moon, will occur. In the western hemisphere, the moon won’t rise until after it is full — but it will still appear full all night long. Actually, in the hours after the full phase occurs, binoculars or telescopes will reveal that the craters arrayed along the moon’s eastern limb are casting shadows — while the rest of the moon will appear “flat”. (Remember that the moon’s eastern edge, or limb, is on the same side as west is, on Earth.)
Indigenous groups have their own names for the full moons, which lit the way of the hunter or traveler at night before modern conveniences like flashlights. The Ojibwe people of the Great Lakes region call this one Mshkawji Giizia, the “Freezing Moon”. The Cree people of North America call it Pimahamowipisim, the “Migrating Moon”, when the birds fly south.
The October full moon always shines in or near the stars of Cetus and Pisces. Since it’s opposite the sun on this day of the lunar month, the full moon rises at sunset and sets at sunrise. This full moon will occur a few days after the moon reaches its greatest distance from Earth, or apogee — producing the smallest full moon of 2019. The opposite of a Supermoon — perhaps this one should be called a Punymoon!
On Wednesday night, the waning gibbous moon will leave Pisces and Cetus and enter Taurus (the Bull). By dawn on Thursday, the moon’s orbital motion will bring it near the triangular face of the bull. But only observers in the Eastern Hemisphere can see the moon caress the bull’s northern cheek!
On Friday overnight, the approximately half-illuminated moon will land between the horns of Taurus, the upraised club of Orion (the Hunter), and the toes of Gemini (the Twins). That weekend moon will rise near midnight and linger into the morning daytime sky.
Mercury and Venus will continue to occupy the western post-sunset sky this week. Venus is currently shifting farther from the sun. The shallow evening ecliptic will prevent Venus from climbing above the glare of sunset for a while longer, but its bright magnitude -3.85 gleam will make it fairly easy to spot for a brief period after sunset, if you can find a low open horizon to the west-southwest.
Much less bright Mercury will be positioned less than a fist’s diameter to the left (or celestial southeast) of Venus this week. On the evening of Sunday, October 20, Mercury will reach its widest separation (25 degrees east) from the sun for the current apparition. With Mercury south of a shallowly dipping evening ecliptic, this has been a poor appearance of the planet for Northern Hemisphere observers, but an excellent one for those at more southerly latitudes. The optimal viewing period for mid-northern latitudes falls between 6:45 and 7 pm local time. Viewed in a telescope Mercury will exhibit a waning gibbous phase. (Venus will look almost fully illuminated.)
Jupiter will be setting in the west soon after 9 pm local time this week, but the earlier-arriving sunsets of October are still giving time to view the spectacularly bright planet. As the sky begins to darken this week, look for the giant planet sitting less than two fist diameters above the southwestern horizon. Jupiter has spent this entire year below the stars of Ophiuchus (the Serpent-Bearer) and above Scorpius (the Scorpion). It will spend next year sitting quite close to Saturn!
On a typical night, even a backyard telescope will show you Jupiter’s two main equatorial stripes and its four Galilean moons — Io, Europa, Callisto, and Ganymede looking like small white dots arranged in a rough line flanking the planet. Good binoculars will show the moons, too! If you see fewer than four dots, then the missing ones are in front of Jupiter, or hidden behind it. Or, it might be that some moons are not being illuminated by sunlight because they are in eclipse!
From time to time, the small, round, black shadows cast onto Jupiter’s surface by those four Galilean moons become visible in amateur telescopes as they cross (or transit) Jupiter’s disk. Tonight, Sunday evening, October 13, observers in the Americas can see a rare double-shadow transit on Jupiter. At dusk, Europa’s shadow will be midway across the northern hemisphere of the planet — accompanied by the Great Red Spot. Shortly before 8 pm EDT, Io’s shadow will join in the fun. Two shadows will both be visible for approximately 35 minutes — until Europa’s shadow moves off the planet at about 8:28 pm EDT. Io’s shadow transit will end at 10 pm EDT — after the planet has set for more easterly observers.
The story will repeat next Sunday evening, October 20 — but only for observers in western North America. At 6:47 pm Pacific Time (in twilight), Io’s shadow will join Europa’s shadow already in progress. The two shadows will cross (at different Jovian latitudes) until 8 pm PDT, when Europa’s shadow will depart, leaving Io’s to complete its passage as Jupiter is setting.
Note that as long as Jupiter is above the horizon for them at the appointed time, everyone on Earth will see the same Jupiter events. If you are not in the Eastern time zone, add or subtract the correct number of hours for your own zone.
Due to Jupiter’s rapid 10-hour rotation period, the Great Red Spot (or GRS) is only observable from Earth every 2nd or 3rd night, and only during a predictable three-hour window. The GRS will be easiest to see using a medium-sized, or larger, aperture telescope on an evening of good seeing (steady air). If you’d like to see the Great Red Spot in your telescope, it will be crossing the planet tonight (Sunday evening) from dusk until 9:30 pm EDT, on Friday, October 18 from dusk to 9 pm EDT, and on Sunday, October 20, starting at 8 pm EDT.
Yellow-tinted Saturn is in the southern evening sky, too — but it is rather less bright than Jupiter. The ringed planet will be visible from dusk, when it will be about 2.5 fist diameters above the southern horizon, until almost 11 pm local time. Saturn’s position is just to the upper left (or celestial east) of the stars that form the teapot-shaped constellation of Sagittarius (the Archer) and about 2.5 fist diameters to the upper left (or celestial east) of Jupiter.
A look at Saturn is well worth dusting off your old telescope! Once the sky is dark, even a small telescope will show Saturn’s rings and several of its brighter moons, especially Titan! Because Saturn’s axis of rotation is tipped about 27° from vertical (a bit more than Earth’s axis), we can see the top surface of its rings, and its moons can arrange themselves above, below, or to either side of the planet. During this week, Titan will migrate counter-clockwise around Saturn, moving from the right of Saturn tonight (Sunday) to the upper left of the planet next Sunday. (Remember that your telescope will flip the view around.)
The next planet in the line of evening planets, distant and dim, blue Neptune is visible all night long among the stars of eastern Aquarius (the Water-Bearer), and is less than a finger’s width to the right (or celestial west) of a medium-bright star named Phi (φ) Aquarii. Both blue Neptune and that golden-coloured star will appear together in the field of view of a backyard telescope at medium power. The distance between the star and the planet is steadily increasing due to Neptune’s westward retrograde orbital motion.
Blue-green Uranus will be rising in the east at 7 pm local time this week. It will remain visible all night long because it is only a couple of weeks ahead of its annual opposition date — when it will appear at its closest and brightest for 2019. The planet is sitting below (or to the celestial south of) the stars of Aries (the Ram) and is just a palm’s width above the circlet of stars that form the head of Cetus (the Whale). At magnitude 5.7, Uranus is actually bright enough to see in binoculars and small telescopes, under dark skies. You can use the three modest stars that form the top of the head of the whale (or sea-monster in some tales) to locate Uranus for the next several months — because the distant planet moves so slowly in its orbit.
Mars is now pulling away from the sun’s glare in the eastern pre-dawn sky. It rises at about 6:15 am local time and will become more easily visible later this month. Unfortunately, the red planet is on the far side of the sun from us — so it will remain rather small and faint until early next year.
Bright October Stars
Around its full phase, bright moonlight tends to overwhelm many of the medium-bright and dimmer stars. So let’s review some of the very bright stars you can see on any night this week.
It’s a good idea to learn the brightest stars, and this time of year, three of the brightest ones hug the horizon. Orange Arcturus is the brightest star in Boötes (the Ploughman). The eye-catching magnitude 0.15 star twinkles brightly, low in the western sky after sunset. It’s the fourth brightest star in the night sky, globally.
The white star Fomalhaut shines in Piscis Austrinus (the Southern Fish). Look for that star sitting low over the southern horizon. It never gets very high for Canadians, but it’s nearly overhead for observers at low latitudes. Fomalhaut is only the 18th brightest star, but dominates in its sparse celestial neighbourhood. It’s also the first star to have an exo-planet directly imaged!
In early evening, bright, yellow Capella sits low in the northeastern sky, ready to begin its nightly passage of the heavens. Sun-like Capella precedes the great starry ring of its constellation Auriga (the Charioteer) and is the sixth brightest star in the heavens.
Finally, the three bright, blue-white stars of the Summer Triangle, namely Deneb, Vega, and Altair, are still flying high overhead.
Astronomy Skylights for the week of October 13th, 2019 by Chris Vaughan.
Keep looking up, and enjoy the sky when you do!
