September 2005 Skies

Introduction:
The month of September marks the end of Summer .  Each day is a bit shorter and each night a bit longer as we approach Autumn and then Winter.  However, Summer’s spectacular stars and constelhelations remain visible most of the night, and the Milky Way presents excellent opportunities for stargazing with binoculars and small telescopes.

[One excellent way to enjoy Astronomy in September is to take a “Field Trip”!!  Here is a list of several interesting and exciting Arizona Astronomy and Earth Sciences Field Trips. Three sites are located in Greater Phoenix, while other trips (including some to cooler locations) may require a 1-day or 2-day Mini-Vacation!]

As Mars continues to brighten in the night sky, it rises earlier each September night, and keeps moving higher in the night sky. Mars is now the 4th brightest object in the night sky, only outshone by the Moon, Venus, and Jupiter. By the end of September Mars will equal Jupiter’s brightness and (being “up” all night) will dominate the sky on moonless nights.

The Sun: The SUN begins the month in the constellation LEO, but moves into VIRGO on September 16th and spends the rest of the month there.  In early afternoon Arizona Time on September 22 the Sun crosses the Celestial Equator and moves into the celestial Southern Hemisphere.  This date marks the Autumnal (or Fall) Equinox or the beginning of the Autumn (Fall) season.  On September 22nd our days and nights will be of equal length.  That day the Sun will also rise due East and set due West in our sky.

The Moon:
September’s NEW MOON occurs on the morning of the 3rd in Leo.
The 1st QUARTER MOON is seen on September 11th in OPHIUCHUS.
September’s FULL MOON occurs the afternoon of September 17th in AQUARIUS, and we will see it rise about ten minutes after sunset that evening.
The 3rd QUARTER Moon occurs on September 24th in on the TAURUS-GEMINI border.

In September the Moon passes near four naked-eye planets:
VENUS & Jupiter: Low in the West the evenings of September 6th in VIRGO.
MARS: Overnight the 21st in ARIES and the 22nd in Taurus.
SATURN: Before dawn on the 28th in CANCER.

The Moon also passes near these prominent stars:
Crescent Moon is close to Spica in VIRGO the evening of the 6thth.
Near Antares in SCORPIO the evening of the 10th.
Last Quarter Moon near the Pleiades star cluster in Taurus the morning of the 22nd.

The Evening Sky:
Early September sunsets occur at about 6:45p.m., but the Sun will set noticeably earlier, at 6:05p.m., at month end.

Evening Planets. Mercury, Venus, Mars, and Jupiter.
MERCURY crosses behind the Sun and into the Western sky on September 17th, becoming an evening planet. It will remain very near the Sun in the sky for the rest of the month, and will be very low in the Southwest and invisible through the end of the month.

VENUS, the brightest object in the night sky after the Moon, begins the month very near to Jupiter in VIRGO (watch it change position vs. Jupiter each evening starting about August 29th!!). After it passes Jupiter on August 31st – September 1st, Venus moves quickly across Virgo and into LIBRA on September 17th. Brilliant white Venus displays phases like the Moon. It begins September as a waning gibbous planet (like the Moon before it is Full), and continues to become more like a crescent by month end.

JUPITER, remains in VIRGO all month, but is fast approaching the Sun low in the Western sky after dark.  After passing Venus on September 1st, Jupiter continues to move closer in the sky to the Sun, setting about 8:35p.m. on the 1st (about 2 hours after sunset).  Jupiter sets only 50 minutes after sunset at month end, and is really no longer useful for telescopic viewing at all in September, as it is so close to the horizon.

MARS is visible most of the night, rising about 10p.m. on the 1st, and remains in the constellation of Aries all month. The Red Planet is difficult to overlook when above the horizon, shining a brilliant pinkish color in the Eastern sky. As Earth continues to approach slower Mars in their orbits around the Sun, Mars appears ever larger when viewed in a telescope.  It will be closest to the Earth (and largest and brightest) in late October.

What Else to See?
Don’t miss the Look for the 3 day old Crescent Moon between Venus and Jupiter after sunset on September 6th.

September evenings find the summer Milky Way high overhead, but the densest regions in SCORPIO and SAGITTARIUS are setting earlier each evening. For best viewing, observe these regions early in the month when the Moon does not interfere.  By the Moon’s 3rd Quarter phase (when it rises about midnight), Scorpio and Sagittarius will set too early in the evening for useful telescopic viewing.

High overhead between 8:30 and midnight are CYGNUS (AKA the Northern Cross) and LYRA the lyre will be nearly overhead.  The three brightest stars there are called the “Summer Triangle” (VEGA in Lyra & farthest to the West, DENEB in Cygnus trailing a bit to the East, and ALTAIR, in Aquila to the Southeast).

The excellent positioning of the more northerly parts of the Summer Milky Way in September makes for memorable binocular and telescopic viewing. On Moonless nights, try to trace the Milky Way with your unaided eyes from Sagittarius upwards to the North through OPHIUCHUS, SCUTUM, DELPHINUS, AQUILA, and CYGNUS and CASSIOPEIA.
Along the way are star clusters and nebular clouds in the Milky Way.  Even a small pair of binoculars will reveal a half dozen fuzzy star clouds in these constellations.

As the Moon slowly moves from West to East around the Earth each month, it occasionally occults (or eclipses) background stars.  A few such occultations of stars of 6th magnitude or brighter occur in the second half of September. Check them out here.

The Morning Sky:
Sunrise on September 1st is at 6:03a.m.  Each morning afterward the Sun rises a bit later.  On September 30th, sunrise occurs at 6:25a.m.

Look for the crescent MOON on mornings after Full Moon (starting on the 18th) through the end of the month.  The Moon is near MARS on the mornings of the 21st and the 22nd.

Morning Planets: Mercury and Saturn.
SATURN is easily visible all month in the nondescript constellation of CANCER the zodiac crab.  It moves with the background stars rapidly to the West away from the Sun, and rises earlier each morning.  On the 1st, Saturn rises at about 3:20 a.m. in a dark sky, followed by the crescent Moon 40 minutes later. At month end Saturn rises a few minutes after 2a.m. and its higher angle above the horizon makes it much easier to observe with binoculars or a telescope.  Late in the month, Saturn moves very near the famous “Beehive” star cluster. Use binoculars or a small telescope to see this rare sight between September.

Mercury races past the Sun on September 17th again becoming an Evening Planet. Look for Mercury first between the 15th and the 20th of September, when it rises a bit North of East and stands directly below Saturn.  Mercury chases, but does not catch up with Saturn, but both will be easy to spot through the end of the month as yellow-orange Mercury draws near yellow Saturn.  Late in the month, Mercury again reverses direction and heads back toward the Sun.

What Else to See?
The Summer Milky Way is easy to see after midnight, as it reaches high overhead.  It is also cooler in the wee hours, so morning observers are more comfortable in September. Binoculars or a small telescope will help you pick out many star clusters, star clouds and gas clouds (nebulae) by sweeping along the arc of the Milky Way from Cassiopeia in the Northeast to Sagittarius in the Southwest.  (Note the online star chart below.)

The constellation ORION rises by midnight at the end of the month and (along with Venus and Saturn) clearly dominates the September morning sky.  The famous Orion Nebula is seen as the middle star in Orion’s “sword” hanging underneath his signature 3-stars-in-a-line Belt.  From a dark location, the unaided eye will see that something is “different” about this “star”. It appears fuzzy and indistinct compared to the nearby stars. Binoculars show it as very fuzzy and perhaps with a gaseous background.  A small telescope reveals the Orion Nebula’s true nature – It is a compact star cluster of several extremely bright blue-white (and very young) stars surrounded by a diffuse cloud of gas and dust left over from the formation of the star cluster.  Strong light pressure and interstellar magnetic fields are shaping the gas into long streams and wisps.

The Orion Nebula is an excellent object to view in an outdoor Star Party later in the year (when it rises early in the evening).

Good Luck Observing!