September 2023 - Vol. 27, 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 reaches inferior conjunction on the 6th, it returns mid-month and presents the best morning apparition of 2023 for the northern observers. VENUS rises higher in the morning sky this month, shining its brightest on September 19 when it is -4.8 magnitude. MARS at +1.8 magnitude, continues to shrink as it approaches the Sun. Mars will be occulted by the Moon on September 16, visible in the daylight through a telescope. JUPITER in Aries, rises in the evening sky. SATURN in Aquarius, begins to fall behind Earth after last month's opposition. The ringed planet will still shine strong in the evening sky. URANUS rises in the evening sky. NEPTUNE reaches opposition on September 19 in the evening sky.

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
01	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. Neptune 1.4 deg. N. of Moon occultation from Parts of W. Antarctica, S. Georgia, and S. Sandwich Islands.
03	Venus stationary.
04	Jupiter 3 deg. S. of Moon. Jupiter stationary.
05	Uranus 3.0 deg. S. of Moon. Moon 1.2 deg. S. of the Pleiades (M-45).
06	Mercury at inferior conjunction.
10	Pollux, Alpha Geminorum 1.5 deg. N of the Moon.
12	Moon at apogee.
15	Mercury stationary.
16	Mars 0.7 deg. S. of Moon occultation from most of N. America, Carribean, Centeral America, northern S. America. May be observable in the daylight hours with a telescope.
19	Venus greatest extent illuminated. Neptune at opposition.
21	Antares, Alpha Scorpii, 0.9 deg. S of the Moon, occultation from E. Khzakhstan, SE Russia, Mongolia, most of China, Japan, N. Philippines, NE Micronesia.
22	Mercury at greatest elongation W (18 deg.)
23	Equinox, the Sun rises due East and sets due West. Mercury at perihelion
27	Saturn 3.0 deg. N. of Moon.
28	Moon at perigee. Neptune 1.4 deg. N. of Moon, occultation in extreme south, also southernmost part of New Zealand.
29	September's full moon is often called the "Harvest Moon" because it is the time of year that farmers in North America harvest many crops.

Lunar Almanac for September 2023

Phases of the Moon	Phase and Date(s)	Best viewed before local midnight
	New 14	Deep Space Objects
	1st. Qtr 22	Planets & Moon
	Full 29	Moon
	Last Qtr 06	Deep Space & Planets

Topic of the month: Ophiuchus, the Serpent Bearer

The Summer sky merits a good long look into Ophiuchus, the constellation of the serpent bearer. It is called this because it splits the constellation of Serpens into two parts. Owing to its lack of bright stars, (none over 2nd magnitude) and its unpronounceable name (O-fee-u-kus), this constellation may remain obscure to casual observers.

Ophiuchus is generally identified with Aesculapius, a mythological doctor. The staff of Aesculapius wrapped with serpents is a well-known medical symbol. A good deal of this constellation is on the ecliptic (more than Scorpius), and its field is resplendent with globular clusters, because it lies near the center of our galaxy.

Two fine globular clusters, visible in the same wide angle field, M-10 and M-12 are beautiful specimens. M-12 is closer, larger and looser than M-10. The other Messier globulars in Ophiuchus include M-14, M-19, M-62 and M-107, but these are not as spectacular as the first two.

Ophiuchus also contains some beautiful star clusters, notably NGC 6633 which contains about 65 stars of 7th magnitude, and IC 4665, a loose cluster of 7th magnitude stars that is quite nice in binoculars or a wide angle telescopic eyepiece.

Nor is Ophiuchus without double stars. Tau Ophiuchi is a close pair of stars, mag 5.3 and 6.0, that require at least 75 mm of aperture to separate. 36 Oph contains two orange dwarf stars shining at 5.3 magnitude. 70 Oph is more well known, once suspected of harboring planets. It is a color contrasting double with orange and yellow components that need 100 mm of aperture, high power and good seeing to separate. William Herschel proved that the two stars were orbiting a common center, providing proof that Newton's law of gravitation worked outside of the solar system

Ophiuchus also contains more than a few planetary nebulae, the best of these is probably NGC 6572, 10th magnitude. Perhaps the most celebrated of all objects in this fascinating constellation is Barnard's Star, the star with the highest proper motion of all known stars. Barnard's star does have at least one planet, it is a red dwarf and at 9.5 magnitude it can't be seen without a telescope.

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