What's Up in the Night Sky

September 2019 - Vol. 23, No. 9

This Month's Night Sky - NOTE: The next paragraph describes the sky as it appears at 10 pm EST (11 pm EDT) near mid- month. The sky also looks this way at 11 pm EST (midnight EDT) during the beginning of the month and at 9 pm EST (10 pm EDT) by month's end.

The Summer Triangle asterism, Vega (Lyra), Deneb (Cygnus) and Altair (Aquila), is still quite prominent overhead as darkness falls. Arcturus (Bootes) is now dipping to the NW horizon. From a dark site, the myriad stars of the Milky Way (the visible "arm" of our galaxy), "flow" eastwards through the "W" asterism of Cassiopeia and to bright Capella (Auriga) glowing in the NE. "The Great Square of Pegasus" asterism burns high in the SE while lonely Fomalhaut (Piscis Austrinus)shines far below, very close to the horizon. "The Big Dipper" asterism (Ursa Major) is nearly horizontal and now sits low on the N horizon. In the E, Aldebaran (Taurus) shines, a sure sign of Autumn.

MERCURY returns to the evening sky in the middle of the month after reaching superior conjunction on on the 4th. It will be more easily seen from the southern hemisphere. VENUS will return to the evening sky mid-month as well, but may be hard to find in the twilight sky. MARS is too close to the Sun to be seen this month reaching conjunction on Sep 2. The red planet is about as far as it can get from Earth and won't be visible until late October. JUPITER is still prominent in the evening sky this month. SATURN will be visible in the evening sky this month. URANUS rises before midnight. NEPTUNE reaches opposition on the 10th.

Review how to determine Angular Measurement.

Calendar of Events

NOTE: For those observers not in the ET zone, convert the calendar times to your zone's time by subtracting one hour for CT, two for MT and three for PT. Don't forget to adjust for Daylight Savings Time when necessary by subtracting one hour from your planisphere's time. Dawn and dusk times must also be corrected. See your local newspaper, TV news, or cable TV's Weather Channel for sunrise and sunset times or check with the U.S. Naval observatory. Unfortunately some of these events may occur during daylight hours in your area.

DATE	EVENT
02	Mars in conjunction with the Sun
04	Mercury in superior conjunction.
06	Jupiter 2.0 deg S. of Moon.
08	Saturn 0.04 deg N. of Moon, occultation from E. Africa, Madagascar, S. Indonesia, parts of Australia, W. Micronesia, and W. Melanesia.
09	Pluto 0.1 deg S. of Moon, occultation from Polynesia except Hawaii, Easter Island, Galapagos Is., and northern South America. (Need a large scope for this event!!)
10	Neptune at opposition.
13	Moon at apogee.
17	Uranus 4 deg N. of Moon.
23	Equinox, the Sun rises due East and sets due West.
24	Moon .04 deg N. of Beehive cluster (M-44).
26	The Zodiacal Light or "false dawn" is visible in the E about 2 hours before sunrise. This pyramidal glow is caused by meteoroids, dust particles spawned by passing comets, etc., that have settled into the ecliptic plane (path followed by the Sun, Moon and planets), reflecting the Sun’s light before it rises here. This phenomenon will be visible until about October 10th as long as the Moon does not interfere.
28	Moon at perigee, expect large tides. Mercury 1.4 deg N. of Spica.

Lunar Almanac for September 2019

Phases of the Moon	Phase and Date(s)	Best viewed before local midnight
	New 28	Deep Space Objects
	1st. Qtr 07	Planets & Moon
	Full 14	Moon
	Last Qtr 21	Deep Space & Planets

Topic of the month: Andromeda and Perseus

In the northern hemisphere as the summer gives way to autumn, sky watchers remember the story that the constellations enacted in the sky, the story of Andromeda and Perseus. This is due to the prominence of the circumpolar constellations of Cassiopeia (The Lady in the Chair) and Cepheus (The King) as they appear to rise in the eastern sky after the sun sets. The constellations of Andromeda and Persues follow behind, and are visible in the evening sky on fall nights.

In Greek mythology, Andromeda was the daughter of Cepheus and Cassiopeia, king and queen of Ethiopia. Queen Cassiopeia boasted that Andromeda was more beautiful than the Nereids, nymphs who were followers of the god of the sea, Poseidon. This made Poseidon very angry and to punish the queen for her arrogance, he sent a sea monster named Cetus to ravage the coast of Ethiopia. Because of the suffering of the people, King Cepheus consulted the oracle of Apollo, who told the king that there would be no respite unless he sacrificed his daughter, Andromeda, to the monster. The beautiful Andromeda was chained to a rock on the coast. Fortunately for Andromeda, the hero Perseus spotted her as he was flying past on his magic winged sandals. Perseus was on his way to the island of Seriphos returning his task of slaying the Gorgon, Medusa. Perseus saw the plight of Andromeda, and showed the head of the Gorgon to Cetus, turning the sea monster to stone. He set Andromeda free and the two were married. Like all characters in Greek myths, they lived far from happily ever after.

fall sky image

The prominent stars in this story light up the fall nights. The constellation Cassiopeia is also called the celestial "W" or "M" after the letters they resemble. There is a double star cluster in this modern constellation that is often referred to as the "double cluster." They are visible to the naked eye from dark sites. The Milky Way galaxy is bright in this constellation, the spiral arm extending in Perseus. The bright star Beta Persei is also known as Algol or the "Demon Star", representing the head of the Medusa. This variable star, was the first variable star of its type recognized, called an eclipsing variable. It is really a star system comprised of three stars. The brightest of these, Beta Persi A, is regularly eclipsed by the dimmer component, Beta Persei B, this causes the apparent magnitude of the star to fluctuate from 2.1 - 3.4 every two days. The eerie nature of this star was noted by the Egyptians long ago.

The constellation of Andromeda is best known today for hosting a very large galaxy, called the Andromeda galaxy. Containing over 400 billion stars, this galaxy can be seen by the naked eye from a very dark site. It appears as a large elliptical cloud when observing conditions are right. This galaxy is the largest member of our Local Group of galaxies that includes the Milky Way and another spiral galaxy in the constellation of Triangulum. These are the three major galaxies and a host of other smaller galaxies and star system belong to our Local Group.

--See You Under the Stars!
Astra for Astra's Almanac