September 2004 Skies

September marks the end of Summer.  The SUN begins the month in the constellation LEO, but moves into VIRGO on September 16th and spends the rest of the month there.  Near Midnight Arizona Time on September 22-23 the Sun crosses the Celestial Equator and moves into the celestial southern hemisphere, which marks the Autumnal (or Fall) Equinox and the beginning of the Autumn (Fall) season.  So, on September 22nd and 23rd our days and nights will be of equal length.  The Sun will also rise due East and set due West in our sky.

The Evening Sky:  In early September our Valley of the Sun sunsets occur about 6:50p.m., but as  Autumn marches along toward Winter sunset occurs earlier each day – almost 45 minutes earlier by month end. 

The MOON begins the month of September three days past Full.  September’s New MOON occurs on the morning of the 14th in the constellation LEO.  The next evening a very thin “baby” crescent Moon should be seen low in the West about 30 to 35 minutes after sunset.  If you have a clear view down to the Western horizon, you should be able to spot this thin crescent Moon even without binoculars.  Early on the evening of September 19th, the Moon will be approaching the red colored 1st magnitude star ANTARES, in the heart of SCORPIO, the zodiac’s constellation of the scorpion.  Full Moon occurs in the constellation PISCES at about sunrise on the morning of the 28th.  Look for two nearly-Full moonrise on the evenings of the 27th (exactly at sunset – 6:12p.m.) and on the 28th thirty minutes after sunset at 6:41p.m. 

September’s only evening naked-eye planet is JUPITER. However, on the 1st of the month Jupiter is only 9 degrees above the horizon at sunset, and sets only 45 minutes after the Sun.  Because Jupiter is so bright, you might be able to glimpse it very low in the West the first few days of the month.  However, by month end Jupiter will have passed the Sun and moved into the morning sky. 

The Morning Sky:
Early September sunrises occur shortly after 6a.m. but the sun rises about 20 minutes later at month end.  The waning MOON will be visible in the morning sky in the early part of September.  The Moon passes near the Pleiades star cluster in the constellation TAURUS on the morning of September 5th and forms a notable triangle with the planets VENUS and SATURN on the mornings of the 9th and the 10th.  Two days later, on the 12th, the MOON is above and to the left (North) of the bright star REGULUS and the planet MERCURY as they rise about 5a.m.

At the beginning of the month, you will see MERCURY rise an hour ahead of the Sun.  By the next week, Mercury has moved farther West and reaches maximum elongation (angular distance away from the Sun) on September 10th.  That same morning, Mercury passes very close to the bright star Regulus.  Less than one-tenth of one degree apart, the planet and star will appear very close in the sky and even visible together in the same telescopic view, even at high magnification!  Mercury then reverses course, rapidly approaches the Sun, and is lost to view about September 20th. 

VENUS remains all month a bright and spectacular “morning star” high in the East, rising more than three hours before the Sun.  Venus starts the month very close to SATURN in the constellation of GEMINI, but then moves across CANCER and concludes the month in LEO. 

SATURN remains all month in Gemini, each day rising earlier and moving farther away from the Sun.  By month’s end, Saturn rises before 1a.m. and at dawn is seen only 20 degrees from the zenith. 

What Else to See?  September is yet another excellent month for evening viewing of the summer Milky Way.  The Moon rises later each evening (10p.m. on the 4th, and after midnight on the 7th), so there will be plenty of dark early September evenings to enjoy the night sky.  It will be dark by 8:30 pm all month and the Milky Way will be passing high overhead and extending across the sky from the Southwestern to Northeastern horizon.  The bright “Summer Triangle” stars DENEB,  VEGA, and ALTAIR are also high overhead, since the Milky Way runs through the Deneb’s constellation of CYGNUS.  In Cygnus we also find the “dark rift” of interstellar dust which appears to split the Milky Way lengthwise. 

Many interesting objects visible with binoculars or a small telescope are scattered along the September Milky Way, including:  Globular Clusters M55 in Sagittarius M15 in Pegasus; Open Clusters M11 in Scutum and M39 in Cygnus, and the most famous Galaxy, M31 – the Andromeda Galaxy, our Milky Way Galaxy’s closest large neighbor.

The constellation ORION rises by midnight at the end of the month and (along with Venus and Saturn) clearly dominates the September morning sky. 
Observers with small telescopes can watch the Moon occult (pass in front of) stars of 6th magnitude or brighter on the mornings of September 2nd, 5th, 29th, and 30th and on the evenings of September 20th, 23rd, 24th, 25th, 26th, and the 30th.

On Friday evening, September 10th,  the East Valley Astronomy Club hosts a Free Public Star Party at the Riparian Preserve next door to the Gilbert Public Library.  Several telescopes will be set up for viewing many interesting astronomical objects.  The Club will also sponsor an astronomy lecture at 8:00 p.m. inside the Gilbert Public Library.  Admission to the lecture is $3.

Good Luck Observing!