Sky Roundup: October, 2008
October Hues
The month of October sees big orange pumpkins lighting up, ripe red apples falling down, and many green leaves turning colors. Golden yellows, rich reds, burnt umbers, and deep oranges all blaze forth on sunny afternoons across the countryside in a wave of riotous color for the next few weeks.
Of course, these marvelous hues bring out the leafpeepers, that is, the friendly tourists who motor by day to rural parts of Ohio to commune with the colors of nature. Not to be outdone, amateur astronomers also join in the fun, but they prefer to notice nature on clear evenings. They are the starpeepers, that is, the friendly skywatchers who motor by night to rural parts of Ohio to commune with the colors of stars.
In last month’s installment of Sky Roundup, the reddish-orange colors of bright, massive stars were highlighted as a nod to the change of seasons. Throughout the month of October, an array of Autumn hues peep out of the night sky for us to see.
High overhead by 10:00 p.m. this month, the large constellation of Pegasus (the Winged Horse) flies across the sky. By myth, the mighty stallion ridden by Zeus, Pegasus holds a few delights to observe and a subtle Autumn coloring among its stars.
The star pattern itself is plain to see on a clear night. Four stars make up what star charts label as the Great Square (though it really looks like a rectangle, and it is supposed to show the body of a horse). The head and mane extend to the south and west from our perspective, so the horse appears upside-down to observers in the Northern Hemisphere. The front legs of the winged horse extend to the west; only the front half of this mythical horse is portrayed in the star pattern. (See star chart 1.)
 |
| Star chart 1: Look up! The Great Square of Pegasus is seen high in the sky for October. Note the neighboring constellations of Cassiopeia, Andromeda, and Perseus. Note the individual star names as well. These are called "common names" since they are less formal than the Greek and Latin designations. So, the star with the common name of Alpheratz was once formally known as Delta Pegasi, but is now known formally as Alpha Andromedae. |
Two stars in the Great Square are noteworthy. One is Beta Pegasi, the second brightest star in Pegasus and in the upper right of the Great Square. It's a giant red star that fluctuates irregularly in brightness and has a soft subtle orange color to its appearance. The other star (formerly called Delta Pegasi), in the upper left of the Great Square, is known better by its common name Alpheratz, which translates as "the horse's navel" though that star officially appears now as Alpha Andromedae in the neighboring pattern of Andromeda, due to gradual, deliberate motions of Earth in its orbit around the Sun.
A quick star hop northeast from Alpheratz and the Great Square into nearby Andromeda (the Beautiful Maiden) reveals the Andromeda Galaxy (also known by the designation of M31, an entry in the sky catalog of French astronomer Charles Messier). This is our closest, large galactic neighbor in space. Just over a mere two million light-years distant, this spiral giant is thought to resemble our own spiral Milky Way Galaxy both in approximate size and shape. Accompanied by its own visible satellite galaxy (designated M32), the Andromeda Galaxy is easily spotted with the naked eye on clear nights, and looks its best at low magnification in a binocular or a good telescope. (See star chart 2.)
 |
| Chart 2: Andromeda Galaxy, M31, is a galactic neighbor and easily seen with telescope, binocular, or eyes alone. Note its labeled position from the upper-left corner star, Alpheratz, of the Great Square. The slightly reddish star Beta Pegasi (unlabeled) anchors the upper-right corner of the Great Square. Note, too, from this less overhead angle, the constellation Cetus near to the horizon. |
Though virtually colorless in the field of view of an amateur's instrument, this galaxy reveals rich hues in other wavelengths as imaged by several of NASA's orbiting spacecraft. The other-worldly color-coding of M31 reveals much to scientists about the structure and star-forming regions of our galactic neighbor. (See comparison slide.)
 |
|
Comparison slide: A different set of views of the Andromeda Galaxy as seen through the electronic eyes of several NASA spacecraft. Image credit: NASA.
|
Below Pegasus and Andromeda in our sky is the lengthy star pattern of Cetus (the Sea Monster, or Whale). Too, it boasts one of the more famous variable stars, Omicron Ceti, better known by its common name Mira or "The Wonderful" (as named by astronomer Johannes Hevelius of Danzig in 1642), owing to its appearance as it fluctuates in brightness. Mira is both a red giant variable star and a binary star speeding through space on its own, but changes in brightness over a period of nearly eleven months. Its fame derives from the fact that Mira is the archetype long-period variable star, which means that the star itself changes not only in magnitude, or apparent brightness, but changes in size as Mira literally expands and contracts in volume due to fluctuations in its internal fusion furnace. Greater volume means a greater surface area and subsequent brightness, at least as we see it in our sky. It was last brightest in our sky last January. When brightest, it glows with the color of a pumpkin in Autumn.
In nearby Perseus (the Hero), another reddish-orange variable star makes its periodic appearance. The star Beta Persei, known better by its common name Algol, goes through a cycle of variability in brightness nearly every three days. The star diminishes in brightness, then it flares up again, since it, like Mira, is a binary system. However, light from this two-star system dims due to the passage of one star in front of another star as we view it along our line of sight. This kind of variable star is recognized as an eclipsing binary, since the two stars in this system alternately block light from its companion. One of the stars in this system appears reddish-orange in color, giving the star we in the sky its distinct hue. Algol is also nicknamed the "demon star" owing to its placement in the constellation Perseus as the baleful eye of Medusa, the Gorgon.
The mythology of this part of the sky tells a bold tale of heroism, set into motion by the star pattern Cassiopeia, which represents the outline of a prideful queen who boasted of her own beauty and that of her daughter, Andromeda. According to the myth, the gods themselves frowned on excessive pride and so punished the queen and her daughter by having Andromeda chained to a rock, where the mighty sea creature Cetus might ravage her. Her champion, Perseus, speeds to her rescue, after slaying the ugly snake-haired Gorgon, whose countenance was so hideous that one would turn to stone on merely gazing at it. Bearing the severed head of Medusa as he rushes to release Andromeda from bondage, Perseus confronts Cetus, forcing the monster to behold the gaze of the Gorgon, whereupon the sea creature rises from the waves high enough for Perseus to slay him. Of course, Perseus frees Andromeda, and both live happily ever after. By the way, just to show that it regularly dims in brightness, Algol's variability is listed in this month’s Sky Almanac.
In searching the skies for the characteristic colors of Fall, let's not forget the familiar face of the Moon. In Autumn, the deep somber orange of the rising Moon casts its light across the landscape. An effect seen often when the Moon is at or near its full phase, the color of pumpkins is not the real hue of the Moon itself; rather, part of its light, reflected from the Sun by the rough lunar surface, gets absorbed as it passes through the Earth’s atmosphere, hence we see only a portion, the reddened wavelengths, of that lunar light. So the Moon appears orange on rising or setting.
That carroty face is often called the Harvest Moon, and it does indeed occur; but, to be accurate, that's actually the closest Full Moon to the autumnal equinox, the astronomical start of the Fall season, which occurs in late September. The genuine folklore name for the rising Moon in October is the Hunter’s Moon. Where the Harvest Moon presumably allowed extra light for farmers to complete the chore of harvesting their fields after sunset, the Hunter's Moon, which occurs one lunar month later during October, allowed the frontiersman extra light at night to hunt game to add to the winter's larder.
This is just a sampling of the colors of Autumn and of the colorful lore brought about by October hues.
Sky Roundup Almanac for Cleveland, October, 2008
October 2: Algol at minimum brightness in Perseus
October 3: Bright star Antares less than 1° north of Moon; no occultation seen here
October 5: Algol at minimum brightness in Perseus
October 7: First Quarter Moon; Draconid meteors at their peak
October 8: Algol at minimum brightness in Perseus
October 10: Neptune less than 1° south of Moon; no occultation visible here
October 11: Algol at minimum brightness in Perseus
October 14: Full Moon; Algol at minimum brightness in Perseus
October 17: Waning gibbous Moon less than 1° north of Pleiades; Algol at minimum
brightness in Perseus
October 19: Algol at minimum brightness in Perseus;
October 20: Orionid meteors at their peak
October 21: Last Quarter Moon
October 22: Mercury at greatest elongation, i.e., greatest angular distance west of Sun;
Algol at minimum brightness in Perseus
October 25: Algol at minimum brightness in Perseus
October 26: Venus north of Antares
October 28: New Moon; Algol at minimum brightness in Perseus
October 31: Bright star Antares less than 1° south of Moon; no occultation seen here;
Algol at minimum brightness in Perseus