A Gorgeous Quarter Moon meets Saturn, and the Swan’s Wings bear its Best Features!
September Stargazing Round-up — Cygnus
With darkness falling a bit earlier, now’s a good time to tour the stars. Objects in the sky directly overhead will always appear at their best because you are looking through the least amount of intervening air. In early evening in late-September every year, the constellations of Lyra (the Harp), Cygnus (the Swan), Hercules, and Draco (the Dragon) surround the zenith. I posted a sky chart here. For a few weeks, we’ve been featuring them, pointing out some objects you can look at with binoculars and small telescopes. I posted our tour of Hercules last week here. Up next is Cygnus!
Head outside on the next clear evening, face east, and look nearly overhead for the very bright star Vega. Below it is the realm of the great constellation Cygnus (the Swan). It is also known the Northern Cross, which is an asterism (or star picture). In size, Cygnus is the 16th largest of the 88 official constellations. Technically, it’s a northern sky constellation — completely above the celestial equator and with a few of its stars circumpolar for mid-northern latitudes around the world.
The constellation is one of the few that truly resembles its name. Cygnus occurs in Greek mythology as Zeus, who used the form of a beautiful swan to seduce Leda, the mother of Helen of Troy. It is also said to represent mourning Orpheus — his harp situated nearby in Lyra. The Arabs saw a hen, the Dakota people saw a salamander and the Ojibwa people saw a crane, the Mongolians saw a bow and arrow, while the Chinese used a different grouping of stars and formed a river crossing.
From Vega, move 23° or 2.3 fist diameters (held at arm’s length) to the lower left. The bright blue-white star Deneb marks the tail of the swan, and actually means “tail” in Arabic. Deneb is a very distant (~1,550 light-years away) luminous supergiant star that shines many tens of thousands of times brighter than our Sun. The slow wobble of the Earth’s axis will cause Deneb to become the North Pole Star around AD 9,800, as it was around 16,000 BC.
About a palm’s width to the right of Deneb is another prominent star which marks the centre of the swan’s body. It is called Sadr, Arabic for “the hen’s breast”. Sadr is about as far away as Deneb, and is also extra luminous, but cooler than Deneb, giving it a warmer colour.
The swan’s head, a modest star named Albireo sits approximately 16° (1.6 fist widths) to the right of Sadr — swans have long necks! It sits in the centre of the Summer Triangle. Albireo is a favorite of summer star parties because it is a coloured double star easily seen in a small telescope. The two stars are a lovely sapphire and gold because they are burning at 11,000 degrees and 4,400 degrees respectively. They sit about 380 light years away and might be slowly orbiting one another.
With these three stars located, forming an imaginary left-right line, you should now be able to locate a long upright chain of well spaced stars forming the swan’s broad wings. Each wing extends about two fist diameters to either side of Sadr and contains three stars.
Moving upwards from Sadr, we first arrive at Al Fawaris (“the Riders) sitting about 8° (less than a fist’s width) away. It has also been known as Rukh, after the giant bird The Roc in Middle Eastern mythology (and some sword and sandal movies). Decent telescopes should be able to split it into a pair of greenish-blue and yellow-white stars. This star will also one day become the pole star. A further jump of 7° to the upper left lands us at white Iota Cygni. And a couple of finger widths beyond that is the wingtip star, yellowish Kappa Cygni.
Moving about 8° downwards from Sadr brings us to the bright yellow-orange star Glenah Cygni, derived from the Arabic words for “Wing of the Swan”. Glenah Cygni is an old star beginning its death processes. Bending slightly to the left and a palm’s width below it is the yellow-orange star Zeta Cygni. Finally, a little more bending and another palm’s width lower is the tightly separated double star Mu Cygni. This pair is orbiting one another every 789 years. And because their orbit is nearly edge on to us, they slowly move closer together and farther apart over the decades. Right now they are separating.
If you can leave the light polluted skies of Toronto, look for some of Cygnus’ wonderful nebulae. Nebulae are clouds of gas and dust that glow in a variety of colours — lit from within by the radiation emitted from the stars they contain. A few finger widths below Deneb is the North American Nebula, named for its shape. Around Sadr lies the Gamma Cygni Nebula, a cloud that is actually six full Moon widths across! Sadr is not associated with the nebula, though. At 1800 light-years distant, it’s only half as far away as the nebula!
About three finger widths to the lower right of Glenah Cygni is the large (five full Moon diameters across!) gossamer pink Veil Nebula or Cygnus Loop. Its roughly circular shape is the tattered remnant shell of a supernova that occurred some five to eight thousand years ago. These large objects are best seen with unaided eyes or binoculars under dark moonless skies — check them out!
If you are in a dark location and the Moon isn’t too bright, you should see that the band of the Milky Way runs right through Cygnus, as if she is about to land for a swim! The rich star fields surrounding the constellation are terrific for reclining and scanning with binoculars. You might find one of the many open star clusters in Cygnus, such as the Foxhead Cluster. Telescope owners should look for the Blinking Planetary. It’s a stellar corpse (like Lyra’s Ring Nebula) that plays an optical illusion on you. When gazing straight at it, its central white dwarf shines as a tiny pinprick. But use averted vision, and the blue halo pops into view. You can make the two views flip back and forth. It’s fun! The object is located about two finger widths to the lower left of the line joining Al Fawaris and Iota Cygni (in the upper wing), and it’s closer to Iota Cygni.
Let me know how your exploration of Cygnus goes. I’ll post a labelled star chart and a close-up picture of the Veil Nebula here.
The Moon and Planets
This is the best week of the Moon’s monthly cycle to observe our celestial partner using binoculars or a small telescope. With First Quarter occurring on Wednesday evening, the moon will be nicely positioned in the evening sky all week. As it waxes fuller every night, the Sun’s light will gradually fill its disk, casting dramatic black shadows from the Moon’s mountain peaks and crater rims — with new terrain highlighted each night. An observer on the Moon would see the sunrise — but it would take all day to climb as much as it does in an hour on Earth!
On Tuesday evening only, the nearly half illuminated Moon will sit only two finger widths above Saturn, making it easy to spot the ringed planet. Saturn will be in the same location all week. For the rest of the week, the Moon hops eastward, first traversing Sagittarius’ teapot-shape, and then through the dim water constellations of Capricornus (the Sea-goat) and Aquarius (the Water-bearer).
If you are out under a clear early evening sky this week, look for Jupiter very low in the west, a short distance south of where the Sun went down. The giant planet sets about 8 pm local time, but your views will be heavily distorted because we have to look through such a deep blanket of air when it sits so low. On the plus side, Saturn is the obvious yellowish object partway up the southern sky as the evening darkens. It sets in the west just before 11 pm local time. Once it’s dark, you can look for the fist-sized Teapot asterism to the left of Saturn and the distinctive Scorpius (the Scorpion), its tail curving eastwards low above the horizon, to the lower right of the ringed planet.
Early risers can check out extremely bright Venus. Recently showing a gibbous phase, it rises in the eastern sky before 5 am local time. This week, the planet continues to descend slowly sunward below Leo (the Lion), moving steadily towards a close rendezvous with dim reddish Mars next week. Mars rises in the east before 5:30 am, a short while after Venus.
Mercury is completing its best appearance of the year for mid-northern skywatchers all over the world, and it’s easily seen with plain old eyeballs for the next few mornings. Look for it as a bright white object very low in the eastern sky. It rises about 6 am local time on Monday morning, but that shifts to about 6:54 am next weekend. You have about a 20 minute window to see it, but it gets harder every morning as it sinks towards the sunrise.
Blue-green Uranus, situated along the eastern (left-hand) string of stars that form Pisces (the Fishes), rises about dusk and is observable for the rest of the night in binoculars under a dark sky. To help guide you, there’s a medium-bright star about a finger’s width below Uranus. Tiny blue Neptune is also observable all night, located about two finger widths to the lower left of the medium-bright star Hydor in Aquarius (the Water-Bearer). But it is too faint to be seen with the unaided eye.
Stargazing News for this week (from September 24th, 2017) by Chris Vaughan.