Maximum Meteors on Monday, the Old Moon’s Crescent Covers a Star, Medusa’s Eye Gleams, and some Binoculars Delights!
The bright evening planets are beginning to “exit — stage west” now. The moon will be absent from the evening sky worldwide as it swings towards the pre-dawn sun. So it’s a great time to explore the fall-winter deep sky treasures with binoculars and telescopes — while temperatures are still mild. Meanwhile, Earth’s nearest planets, Venus and Mars, are both improving in visibility as they increase their angles from the evening and morning sun, respectively. And Mercury has reached peak visibility, too. Here are your Skylights!
The Moon and Planets
Over the first part of this week, the moon will rise in the wee hours and traverse the stars of Gemini (the Twins) on Sunday and Monday, then dim Cancer (the Crab) on Tuesday, and bright Leo (the Lion) on Wednesday and Thursday.
When the moon rises in the eastern sky after shortly before 1 am EDT on Tuesday, it will be completing a passage through the heart of the large, open star cluster known as the Beehive (and Messier 44). The moon’s orbital motion will carry it several degrees away from the cluster by dawn, but both objects will still fit within the field of view of binoculars. For best results, position the moon outside of the lower left of your binoculars’ field of view and look for the cluster’s myriad stars. Hours earlier, observers in Europe and Asia can witness the moon crossing just north of the cluster’s center.
On Friday morning, the old crescent moon will rise at about 4:30 am local time and enter the constellation of Virgo (the Maiden). As it does so, the moon will pass in front of (or occult) a medium-bright star named v Virginis, or 3 Virginis. You can watch the event in a telescope, through binoculars, or with your unaided eyes. At about 5:28 am Eastern Daylight Time (or 09:58 GMT), the bright crescent of the moon will cover the star. At 6:21 am, the star will suddenly re-appear over the dark top edge of the moon. During these lunar stellar occultation events, stars disappear and reappear almost instantly because the moon has no atmosphere to spread out a star’s narrow beam of light. The exact timings will vary by your latitude, so start watching earlier — or use an astronomy app like SkySafari to find out the exact times where you are located. By the way, the moon’s orbital motion around Earth is fast! The moon shifts by its own diameter every hour.
In the eastern sky on Saturday morning, the slim, old, crescent moon will be positioned a palm’s width above (or to the celestial northwest of) the reddish planet Mars. Try to look for them between about 6:30 and 7 am local time.
Next Sunday morning, you might catch a glimpse of the very slim crescent moon sitting just above the eastern horizon before sunrise. Interestingly, the moon will reach its new moon phase just before midnight Eastern Time on Sunday evening. At its new phase, the moon is travelling between Earth and the sun. Since sunlight can only reach the far side of the moon, and the moon is in the same region of the sky as the sun, the moon will be completely hidden from our view until just after sunset on Monday evening.
Mercury and Venus will continue to occupy the western, post-sunset sky this week. Venus continues to shift farther from the sun, but the shallow evening ecliptic will prevent Venus from climbing above the glare of sunset for a while longer. Venus’ bright magnitude -3.85 brilliance 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. It sets shortly after 7 pm local time.
You can use Venus to find comparatively dimmer Mercury. Because Mercury has reached its greatest separation from the sun, and Venus has not, Venus will be shifting closer to Mercury this week. Tonight Mercury will be positioned a generous palm’s width to the left (or celestial southeast) of Venus. Next Sunday, however, Venus will have moved to within four finger widths to the upper right of Mercury. Viewed in a telescope this week, Mercury will exhibit a waning, half-illuminated phase. (Venus will look almost fully illuminated.)
Jupiter will be setting in the west at about 9 pm local time this week, but the earlier-arriving sunsets of October are still giving us time to view the spectacularly bright planet, albeit through a LOT of intervening atmosphere. Still — time is running out for Jupiter-viewing this year. As the sky begins to darken this week, look for the giant planet sitting about 1.5 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!
Yellow-tinted Saturn is still a very good option for backyard telescopes. It’s in the southern evening sky — and 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 about 10:30 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 upper left of Saturn tonight (Sunday) to the lower right of the planet next Sunday. (Remember that your telescope will flip the view around.)
The ice giant planets Uranus and Neptune are both positioned more-or-less opposite the sun in the sky, so each one is a good all-night target.
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 sunset 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 still pulling away from the sun’s glare in the eastern pre-dawn sky. It rises at about 6:10 am local time and will become more easily visible in early November. 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.
Binocular Dark Night Delights
The next two moonless weeks will be ideal for seeing the deep sky gems scattered along the winter Milky Way — and more. Here are some suggestions for binoculars viewing that are bright enough to see, even near city lights.
In mid-evening during late October, the constellation of Perseus (the Hero) is positioned midway up the northeastern sky. This constellation’s location straddling the outer reaches of the Milky Way has filled it with rich star clusters. The largest of these clusters, named Melotte 20, surrounds the bright star Mirfak, or Alpha Persei. Also known as the Alpha Persei Moving Group and the Perseus OB3 Association, the cluster is a collection of about 100 young, massive, hot B and A-class stars spanning 3 degrees (or six full moon diameters) of the sky. The cluster can be seen with unaided eyes, and improves in binoculars. It is approximately 600 light years from the sun and is moving through the galaxy as a group. Mirfak is moving with them. That elderly, yellow supergiant star has evolved out of its blue-coloured phase and is now fusing helium into carbon and oxygen in its core.
The northwestern region of Perseus contains the well-known Double Cluster. Two bright, open star clusters, each 0.3 degrees across and only 0.45 degrees apart, form a spectacular sight covering a single finger’s width of sky. If you face northeast, they will be located midway between W-shaped Cassiopeia (the Queen) and the bright star Mirfak.
You can try to see the pair of clusters without help. They’ll look like two fuzzy patches. Or use binoculars or a low power, widefield telescope to view them in all their glory. The lower, more westerly cluster is also known as NGC 869. It is more compact and contains more than 200 white and blue-white stars. NGC 884, the higher, easterly cluster, is slightly more spread out. Both clusters reside in the Perseus Arm of our Milky Way galaxy and are located about 7,300 light-years from the sun. Their region of the sky is heavily loaded with opaque interstellar dust that extinguishes their intensity.
An extra-galactic treat is nearby. After dusk on October evenings, the Andromeda Galaxy is halfway up the eastern sky. This large spiral galaxy, also designated Messier 31 (or M31), lies a whopping 2.5 million light years from us, and subtends an area of sky measuring 3 by 1 degrees (or six full moon diameters across and two diameters high). Under dark skies, the galaxy can be seen with unaided eyes as a faint smudge to the left (or celestial northeast) of the square of Pegasus (the Horse). The three westernmost stars of Cassiopeia, Caph, Shedar, and Navi, conveniently form a triangle that points towards the galaxy. Binoculars will reveal the galaxy better. In a telescope, use low magnification and look for the two smaller companion galaxies Messier 32 close to M31’s core and Messier 110, which is farther from the core on the opposite side.
Later in the evening, you can look for the bright little star cluster known as the Pleiades, the Seven Sisters, and Subaru (in Japan). It will rise from the north-northeastern horizon after 8 pm local time.
Watch Medusa’s Eye Brighten
The “Demon Star” Algol in Perseus (the Hero) is among the most accessible variable stars for beginner skywatchers. Like clockwork, this star’s visual brightness dims noticeably for about 10 hours once every 2 days, 20 hours, and 49 minutes. That happens because a dim companion star orbiting nearly edge-on to Earth crosses in front of the much brighter main star. Once the eclipse begins, the star steadily drops in brightness for five hours, and then it ramps up again during the second five hours — until the eclipse is over.
Algol represents the glowing eye of Medusa the Gorgon, whose severed head Perseus is carrying. That’s why this star has the nickname the “Demon Star”. Perseus is positioned to the upper left of the bright Pleiades star cluster. Another name for Algol is Gorgonea Prima “the First Gorgon”. The star that sits two finger widths to the right of Algol is Gorgonea Tertia “the Third Gorgon”. By the way, Gorgonea Secunda “the Second Gorgon” and Gorgonea Quarta “the Fourth Gorgon” are the stars Pi (π) Perseii and Omega (ω) Perseii. They sit to the upper right and lower right of Algol, respectively. The four Gorgons stars combine to form Medusa’s box-shaped head.
On Friday, October 25 at 8:51 pm EDT, Algol will reach its minimum brightness of magnitude 3.4 (i.e., the smaller, dimmer star will be fully in front of the larger, brighter star). At that time, Algol will be positioned a third of the way up the northeastern sky. By 1:51 am EDT, Algol will be approaching the zenith and will have brightened to its usual magnitude of 2.1.
The easiest way to detect Algol’s variability is to note how bright Algol looks compared to other neighboring stars. When it isn’t dimmed, Algol is brighter than any other nearby star save Mirfak, which sits a fist’s diameter to Algol’s left (or celestial north). Although Gorgonea Tertia is somewhat variable, too, it shines at about the same brightness as Algol when Algol is at minimum.
With the early sunsets of winter in the Northern Hemisphere, we’ll have many chances to see Algol brighten at convenient times — say, from dinnertime to bedtime.
Orionids Meteor Shower
The excellent Orionids Meteor Shower, which is derived from fine particles dropped by repeated past passages of Comet Halley, runs from September 23 to November 27, and is observable world-wide. The Orionids (for short) will peak in the hours between midnight and dawn (in your local time zone) on Tuesday, October 22. At that time, the sky overhead will be plowing through the densest region of the particle field, generating as many as 25 meteors per hour.
This shower has a broad period of activity — the comet’s debris field is very spread out because the comet’s orbit crosses Earth’s at a shallow angle. While the Orionids will linger until late November, they will decrease in quantity every night after this week’s peak.
The meteors can appear anywhere in the sky, but true Orionids will be travelling in a direction away from a location in the sky called the radiant. It’s positioned a fist’s diameter to the upper left of the bright red star Betelgeuse in the constellation of Orion, which gives this shower its name.
Although not too numerous, Orionids are known for being bright and fast-moving. Unfortunately, the waning, half-illuminated moon will overwhelm the weaker meteors on the peak nights this year. You can watch for meteors on Monday before midnight, too — but many of them will be obscured by the Earth’s horizon.
To see the most meteors, get away from light-polluted urban skies and find a dark site with plenty of open sky. Don’t bother with binoculars or a telescope — their fields of view are too narrow for meteors. And don’t watch the sky near the radiant — those meteors will be travelling towards you and will produce very short streaks. Just keep your eyes on the sky overhead.
You can start watching as soon as it is dark, or head outside before the dawn twilight begins. Avoid bright white light from phones or tablets — it will spoil your eyes’ dark adaptation (red light is fine). If the peak night forecast calls for clouds, try the nights before or the nights after. Happy hunting!
Astronomy Skylights for the week of October 20th, 2019 by Chris Vaughan.
Keep looking up, and enjoy the sky when you do!