THE SOUTHWORTH PLANETARIUM

70 Falmouth Street Portland, Maine 04103

(207) 780-4249 usm.maine.edu/planet

43.6667° N 70.2667° W

Founded January 1970

2022-2023: VI

Sunrise: 6:10 a.m.

Sunset: 7:08 p.m.

Civil twilight ends: 7:37 p.m.

Sun's host constellation: Leo the Lion

Moon phase: Waxing gibbous (80% illuminated)

Julian date: 2459829.16

"These are my principles. If you don't like them, I have others." -Groucho Marx

THE DAILY ASTRONOMER Tuesday, September 6, 2022

September 2022 Sky Calendar Part I: The Stars

We've now reached the "numerated months," defined as those whose names are based on numerical order rather than mythological characters/events or historical figures. Let's review:

January: named after Janus, the god with two faces oriented in opposite directions. The younger face is directed toward the future, while the older face peers into the past. Janus is also the god of doorways. An apt name for the first month of the year.
February: named after Februus, the Roman god of purification or after Februa , the purification ritual performed in his honor. The second month was named after Februa simply because that was the time of year when these rites were performed.
March: named after Mars, the Roman counterpart to Ares, the god of war. Considering the weather we generally experience in March, naming it after the god of violence, tumult and madness seems quite appropriate
April: while the origin of this name is disputed, this month was not named for Aphrodite, goddess of love and beauty, as is often believed. It is likely that the month was named for the Latin term "aperio," meaning "to open" or "to bud," in reference to the first of the spring flowers that rise and unfurl their blossoms at this time.
May: named for Maia, the Roman goddess of growth and plants. Quite apropos.
June: named for Juno, the Roman counterpart to Hera, goddess of marriage. She was perhaps the most ironical of all deities, for this goddess of marriage was wed to Zeus, the most incorrigible of all philanderers. The long suffering Hera (Juno) lived in a state of perpetual rage due to her husband's all too frequent indiscretions. All the same, unlike her skirt-chasing spouse, Juno became the namesake of a month.
July: named for Julius Caesar, the first dictator of Rome. He was deified after his assassination and in apotheosis assumed an array of powers associated with his more mythological cohorts.
August: named for Augustus Caesar, the first emperor of what on his accession became Imperial Rome. The name "Augustus," itself, was a title conferred on him after assuming the role of Rome's only ruler. His original name was Octavian.
September: the "seventh" month, or so it was when March was designated as the year's first month. Although the switch to January as the year's first month was first decreed in the 2nd century BCE following a proposal approved in the Roman Senate, the new year was still often celebrated in March in many regions. Only after the Gregorian calendar reform in 1582 was January firmly established as the year's first month.
October: the "eighth" month
November: "the ninth" month
December: "the tenth" month.

We've entered the last third of the year, a time when the bright summer constellations remain visible while the fainter autumn patterns ascend into greater prominence. Before we proceed with an itemized list of significant astronomical happenings, we'll devote some time to the constellations one can easily observe this month.

Along the Milky Way's Arc

Finding the Summer Triangle is literally as easy as looking straight up in the early evening. This immense three-star pattern consisting of Vega, Deneb and Altair begins the night directly overhead. Vega, the brightest of the three ST stars, marks the northern tip of Lyra, the lyre on which the mythical Orpheus performed when he persuaded Hades and Persephone to release the recently deceased Eurydice from the Underworld. Altair, the second brightest Summer Triangle star, forms the tail of Aquila the Eagle, associated with Zeus who transformed himself into an eagle when he abducted the beautiful youth Ganymede. Deneb, which defines the Summer Triangle's northeastern corner, represents the tail of Cygnus, the Swan whose form Zeus assumed when he seduced Leda and by her sired the twin Pollux and Helen. (Yes, the same Helen whose eventual abduction precipitated the Trojan War.) Cygnus is also known as the "Northern Cross." More people have heard of the Southern Cross, which is only visible south of the 30th N parallel. However, for us, the Northern Cross hangs close to the zenith in the September evening sky.

The astronomical points of interest around the Summer Triangle are innumerable. We'll choose only a couple. Albireo, the star at the other end of the Northern Cross' longer axis from Deneb, appears as a single star. However, when viewed telescopically, one observes its two components: one golden yellow, the other sapphire blue. This stark color contrast, combined with their comparatively wide angular separation (35" of arc) makes Albireo one of the easiest double stars to see through even a small telescope. Astronomers are not sure if this pair is a true, gravitationally bound binary system or, instead, an optical double. If Albiero is a true binary, the orbital period of both stars around their common barycenter must exceed 100,000 years!

Albireo, the gorgeous double star at the southern trip of the Northern Cross. Located 214 light years from Earth, Albireo might be an optical double (two stars that happen to be aligned along the same path, but are not gravitationally bound to one another) or a real binary with a period exceeding 100,000 years!

Provided your sky is reasonably dark, you'll notice what appears to be a luminescent cloud band running through the Summer Triangle. The collective light of thousands of stars within the Milky Way Galaxy's disc produce this faint, but noticeable glow. We were to observe our home galaxy from an external vantagepoint, it would appear as an immensely large "whirlpool" of stars, defined technically as a barred spiral. The majority of its stars move along the main disc spanning 100,000 light years. The "Milky Way" band consists of part of this disc, in which the stellar density is so high that the stars appear as a diffuse band of light as opposed to sharp points.

We'll follow this band in two directions: toward the northeast, where we'll find Cassiopeia the Queen, and then toward the southwest where we'll see Sagittarius the Archer.

Mythologically, the constellation Cassiopeia is associated with an ancient Ethiopian queen of the same name. The W-shaped asterism comprising the majority of the constellation represents the ill-fated queen seated on her throne. Her audacious boast that her daughter Andromeda's beauty surpassed even that of the Nereids, nymphs sacred to the ocean god Poseidon, so enraged this deity that he summoned the monster Cetus from the ocean depths to ravage her kingdom. She and her husband Cepheus learned that only by sacrificing their daughter Andromeda to Cetus would they manage to propitiate Poseidon. Fortunately, the warrior Perseus eventually slew the creature and rescued their daughter. After her death Cassiopeia was hoisted up into the sky as the constellation that bears her name. However, being circumpolar, Cassiopeia describes wide circles through the northern sky so that, at times, she suffers the indignity of having to sit upside down: a particularly ignominious, yet arguably condign punishment for her arrogance.

Alpha Centaurians would see our Sun as a bright star within the Cassiopeia region. Our parent star would appear as bright to them as Betelgeuse appears to us.

One of the principal astronomical aspects of Cassiopeia pertains to the Sun! Any sky admiring aliens within the Alpha Centauri system -the closest star to the Sun- would see the Sun close to the pattern we perceive as Cassiopeia. (Refer to the above image.) In fact, our Sun would appear to them as a magnitude 0.46 star (about as bright as Betelgeuse appears to us) just off to the side of the W-asterism. So, from their perspective, we are all "in" Cassiopeia. Of course, if they exist and assuming they have inscribed their mythological characters onto the night sky, Cassiopeia won't be known to them.

At the southwestern part of this arc one will see Sagittarius the Archer, part of the zodiac, defined as the retinue of thirteen constellations through which the Sun appears to travel throughout the year. The Sun "occupies" the Sagittarius region between December 18 - January 18. Currently, Sagittarius begins the night low in the southwestern sky.

Most of Sagittarius' stars are located within the "teapot" asterism consisting of a handle, lid and a spout. Mythologically, Sagittarius is associated with Nessus, the centaur who was killed by Heracles after the former attempted to kidnap Deianira. As he lay dying after having been shot by one of Heracles' arrows, Nessus persuaded Deianira to conceal a bit of the centaur's blood in a phial by explaining that such blood served as a strong love potion. "If you worry that your husband's affections are waning," Nessus said while the furious Heracles approached them, "smear this blood on his cloak and he will be devoted to you forever." Deianira managed to hide the phial just before Heracles arrived to finish off the centaur. A few years later, Deianira became desperately afraid that Heracles had fallen out of love with her as he had lately been quite cool and distant. She slathered the blood on his cloak while he slept and was horrified to see him put on the cloak and start screaming in the most excruciating agony. The centaur blood was actually a lethal poison. Or, it would have been lethal to any mortal. As Heracles had become immortal after the completion of his labors, he couldn't die. However, such was the intensity of his torment, that Heracles begged Zeus to rescind the immortality. Sadly, the god complied with the demand and Heracles promptly jumped on a lit funeral pyre and perished. The remorseful Deianira threw herself on the same flames that consumed her husband. Therefore, Nessus was credited with having killed Heracles a few years after the creature, himself, had died.

Sagittarius also marks the location of the galaxy's center, called the nucleus, located about 26,000 light years from Earth. Within this nucleus one would find Sagittarius A*, a supermassive black hole about four million times more massive than the Sun. One would also encounter a vast array of globular clusters swarming along the halo, the spherical region centered on the nucleus. Unlike galactic, or open, clusters, globulars tend to be immensely large, spanning hundreds or thousands of light years and old, sometimes on the order of 12 -13 billion years, They also harbor huge stellar populations, in the hundreds of thousands or, in extreme cases, millions of stars. These aged objects loiter around the galactic halo, they are only found within a specific region of the sky aligned with the halo, such as the area encompassing Sagittarius.

M22: a globular cluster located 10,000 light years from Earth and one of the many such clusters found within Sagittarius.

Although we can't see these massive clusters, be well assured that they're moving along multi-million year long orbits deep within the dark fields of Sagittarius.

Part II tomorrow.

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