Summer triangle rides high in the night sky
Astronomy columnist Glenn Roberts begins a multi-part series focused on the summer constellations
Now that summer is once again with us, it’s time to renew our acquaintance with the summer constellations. We’ll bypass the circumpolar constellations of Ursa Major — the Big Bear, Ursa Minor — the Little Bear, Draco — the Dragon, Cassopeia — the Queen and Cepheus — the King, as these constellations are visible on any clear night throughout the year.
In the first of a multi-part series on the summer constellations, we’ll begin with three of the summer night sky’s most prominent constellations: Aquila — the Eagle, Cygnus — the Swan and Lyra — the Harp, all of which can be found on a clear night high in the southern part of the sky once the sky has darkened (by about 10 p.m.). The brightest stars in these three constellations — Deneb in Cygnus, Altair in Aquila and Vega in Lyra — serve as vertices of the summer night sky’s wellknown Summer Triangle asterism.
CYGNUS
The constellation of Cygnus (Latin for swan) is associated with a number of ancient myths, perhaps the most famous being that of Leda and the Swan. According to this myth, the Greek god Zeus seduced the mortal Spartan Queen, Leda, by transforming into the figure of a swan. From this most unlikely of unions, plus one with her mortal husband, King Tyndareus, Leda is said to have given birth to two sets of twins — the immortal Pollux and the mortal Helen (later of the Trojan War fame), as well as the mortal Castor and the immortal Clytemnesia (Helen and Castor being the mingled progeny of King Tyndareus and Pollux and Clytemnesia from Zeus).
Pollux and Castor are, of course, better known as the Gemini twins.
Another Greek myth ties Cygnus with the famous Greek harpist, Orpheus. When Orpheus was killed by a group of Thracian Maenads for not honouring the god Dionysus, his body was placed in the heavens by the gods as the constellation Cygnus, while his harp was represented by the constellation of Lyra — the Lyre/harp.
THE MAGPIE BRIDGE
There is also a lovely Chinese myth about the magpie bridge — Que Qiao. In the story, an immortal fairy fell in love with a mortal, but, as such a union was forbidden by the Goddess of Heaven, efforts were made to keep the young lovers apart. When the Goddess of Heaven discovered that the two lovers had been secretly married, she took the fairy to Heaven and placed a large river (the Milky Way) between Heaven and Earth in an effort to keep them apart.
Pitying the two separated lovers, the myth states that, once a year, all the magpies (a type of bird) assembled together and formed a bridge (Que Qiao — the magpie bridge — our modern-day constellation of Cygnus) between Heaven and Earth, thereby allowing the lovers to be re-united.
THE NORTHERN CROSS
In addition to representing a swan, Cygnus contains a famous asterism — the Northern Cross. Both the swan and the cross are represented by five bright stars — Deneb, Sadr, Albireo, Aljanah and Fawaris. Deneb (from the Arabic dhaneb, meaning tail) is a blue-white supergiant star, located approximately 1,400 light years from Earth; it is one of the most luminous stars known (60,000 times that of our Sun).
Interestingly, on Mars, Deneb is the North Star.
Sadr (Arabic for the chest) is a supergiant star, 1,800 light years away and, at magnitude +2.23, one of the brightest stars in the night sky.
Aljannah, an orange giant star, is relatively close to Earth at 72.7 light years.
Fawaris is a triple-star system, located 165 light years from Earth; it will become our North Star for about 400 years around the year 11,250.
Albireo (the beak star), a close binary star system, is around 380 light years away and is composed of a magnitude 3.2 yellow star and a faint magnitude 5.8 blue star (beautiful in binoculars and scopes).
LYRA
Lyra — the Lyre or Harp, is a parallelogram-shaped constellation to the right of Cygnus. As mentioned, it is said to represent the lyre/harp of Orpheus, a renowned musician in ancient Greek mythology. His music was reputed to be so lovely that even the Olympian gods enjoyed it and wept upon his untimely death, placing both his body (Cygnus) and his lyre/harp (Lyra) in the night sky as a symbol of their respect.
Lyra’s brightest star, Vega (magnitude -0.03), is the fifth brightest star in the night sky. Several thousand years ago, it was the North Star and will be again in about another 12,000 years.
One of the other bright stars in the constellation, Sheliak, is a prototype variable star of a class of binary stars which are so close to one another that gaseous material flows from one to the other and the stars actually become egg-shaped.
The remaining bright star in Lyra is Epsilon Lyrae, known as the Double Double (perhaps there is a Tim’s there!), which is, in reality, two sets of binary stars orbiting each other.
AQUILA
In Greco-roman mythology, Aquila is said to represent the eagle that carried the thunderbolts of Zeus/jupiter when he went into battle. This eagle also seems to have earned a place in the night sky after kidnapping (by the gods’ royal decree) the mortal Trojan prince, Ganymede (reputed to have been very handsome), to serve as the royal cup-bearer for the Mount Olympian feasts and celebrations.
The ancient Romans also referred to this constellation as the Vultur volans or flying vulture. The constellation’s brightest star, Altair (from the Arabic phrase al-nasr al-tair — the flying eagle), at only 17 light years distance, is one of the closest naked-eye stars to Earth.
Other bright stars in Aquila include Alshain, a magnitude +3.7 yellow star, at a distance of 45 light years; Tarazed, a magnitude +2.7 orange star at 460 light years; and Okab, a magnitude +3.0 bluish-white star located 83 light years from Earth.
WHAT TO LOOK FOR THIS WEEK
There is a brief window of opportunity in the next few days to view the five bright planets together in the pre-dawn eastern sky, though just barely. Saturn (magnitude +0.6, in Capricornus — the Sea Goat) rises in the east-southeast around 11:50 p.m., reaching a height of 25 degrees in the southern sky before fading from view by about 4:30 a.m.
Jupiter (magnitude. -2.4, in Pisces — the Fish) rises due east around 1:30 a.m., reaching 35 degrees above the southeast horizon before disappearing into the approaching dawn around 5 a.m.
Mars (magnitude +0.5, in Pisces) is visible in the predawn, east-northeast sky shortly after 2 a.m., reaching an altitude of 27 degrees above the eastern horizon before fading from sight, along with Saturn, around 4:30 a.m.
Bright Venus (magnitude -3.9, in Taurus — the Bull), now drawing closer to the sun, and thus lower in the pre-dawn sky, is visible in the east-northeast sky shortly after 4 a.m., but only reaching 13 degrees above the eastern horizon before succumbing to the dawn around 5 a.m.
Mercury (magnitude +0.1, in Taurus) is briefly visible above the east-northeast horizon shortly before 5 a.m., but, in all likelihood, due to its low position, minimal magnitude, and the fast-approaching sunrise, won’t be visible. Still, if you happen to be viewing the pre-dawn sky on June 27, you might, with a clear sky and binoculars, catch a glimpse of Mercury sitting four degrees to the south of the waning, crescent Moon in the northeast sky before it fades from view.
Until next week, clear skies.
When the Goddess of Heaven discovered that the two lovers had been secretly married, she took the fairy to Heaven and placed a large river (the Milky Way) between Heaven and Earth in an effort to keep them apart.
Chinese fable
EVENTS:
June 28: New moon; Moon at apogee (farthest from Earth)
Glenn K. Roberts lives in Stratford, P.E.I., and has been an avid amateur astronomer since he was a small child. He welcomes comments from readers at glennkroberts@gmail. com.