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You've Never Seen A Winged Horse? Look up...

Oct. 18, 2022 | By Geoff Chester, USNO Public Affairs

NGCs 869 & 884, the "Double Cluster" in Perseus, imaged 2018 October 7 from Mollusk, Virginia
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor and a Canon EOS Rebel T2i DSLR.
These spectacular clusters, located in the Milky Way between Perseus and Cassiopeia,
are "showpieces" for small-aperture wid-field telescopes.

The Moon wanes in the pre-dawn sky this week, her slimming crescent passing through the rising springtime constellations as she drops toward the eastern horizon.  New Moon occurs on the 25th at 6:49 am Eastern Daylight Time.  Luna will be located near the stars Algeiba and Regulus in the constellation of Leo, the Lion before dawn on the 20th.

With the Moon now traversing the morning sky, it’s time for the October observing campaign of the Globe at Night citizen-science program.  This project, which was initiated in 2009 as part of the International Year of Astronomy, encourages skywatchers to look at seasonal constellations to measure the brightness of their overhead night skies.  Participation has steadily grown over the years, with about 20,000 citizen observations recorded in 2021.  This month’s target constellation is Pegasus, the winged horse of Greek legend.  The main feature of Pegasus is a large square of second-magnitude stars that is high in the eastern sky by the mid-evening.  This year the planet Jupiter blazes away beneath the eastern side of the square, which should be visible to observers in urban skies.  As you move to darker skies, more stars become visible inside and near the square, and under very dark conditions up to a dozen faint stars can be seen.  If you would like to contribute your own observations, go outside at around 9:00 pm and let your eyes adjust to the darkness.  Look for the “Great Square” of Pegasus in the east, then compare your view with the charts on the Globe at Night web app.                              

Pegasus is one of the players in an age-old story that plays out in the autumn sky.  It is a tale of vanity and revenge that has a hero armed with a secret weapon who rescues an innocent maiden from a gruesome death.  Six autumnal constellations play the dramatis personae in the story.  The story begins with the king and queen of ancient Ethiopia, Cepheus and Cassiopeia.  The queen, whose vanity was known throughout the ancient world, spent much of her time gazing at herself in a mirror, finally declaring that her beauty was greater than that of the Sea Nymphs, the daughters of Poseidon.  Needless to say, this did not sit well with the god of the sea, so he punished Cassiopeia by chaining her daughter Andromeda to a rock, where she would be devoured by the monster Cetus.  Fortunately, the hero Perseus saw Andromeda’s plight as he flew by on Pegasus and rescued the lady by forcing Cetus to look into the eyes of the severed head of the Gorgon Medusa, which he happened to be carrying as a memento of his previous adventure.  Cetus was turned into stone, visible today as the Rock of Gibraltar, Perseus saved Andromeda, and everyone got a place in the night sky.

You can see Andromeda’s chains as two diverging lines of stars that originate from the star Alpheratz, which marks the northeastern corner of the Great Square of Pegasus.  North of Andromeda is the W-shaped asterism formed by the brightest stars of Cassiopeia, and the brighter southern “chain” of the maiden points to Mirfak, brightest star in Perseus.  The constellation’s second-brightest star, Algol, lies about 10 degrees south of Mirfak.  Algol has long been known as the “Demon Star” that represents the eye of the severed head of Medusa.  It fades by a factor of three for a few hours every 2.86 days, then returns to its usual brightness.  Now known to be a double star system in which a dimmer component periodically eclipses a brighter one, to the ancients it fit the Perseus legend perfectly.

Saturn shines among the stars of the faint constellation of Capricornus, the Sea-Goat.  In the mid-evening he forms a large triangle with much brighter Jupiter to the east and the lonely first-magnitude star Fomalhaut low in the southeastern sky.  Saturn shines with a subtle yellow hue thanks to a dense atmosphere is ammonia and methane, but his most outstanding feature is the array of rings that circle above his equator.  They consist of billions of icy bodies ranging in size from microns to large terrestrial buildings that are shepherded by the planet’s inner icy moons.  The planet and his bevy of moons are one of the most mesmerizing sights for the small telescope.

Jupiter continues to be the night’s big draw for telescope owners around the world.  Old Jove shares similar chemistry with the atmosphere of Saturn, but internal heat from deep under his cloud tops keep his atmosphere in constant turmoil.  The two dark equatorial cloud belts are easily seen in small telescopes, but instruments of six inch or larger aperture will reveal many subtle loops and whorls in these dark bands.  If you watch the planet over the course of an hour or so you will see dramatic changes.
 
Mars is approaching the first stationary point for the current apparition.  You can see him rising in the east before midnight, where he forms a ruddy triangle with the similar hued stars Betelgeuse and Aldebaran.  Earth is gradually catching up to Mars, so his apparent disc continues to brighten and grow as we approach his opposition in December.
 
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