September Skies 2006

Introduction:
September marks the end of Summer.  Each September day is a bit shorter and each night lasts a bit longer as we approach Autumn and then Winter.  However, Summer’s spectacular stars and constellations remain visible most of the night, and the Milky Way presents excellent opportunities for stargazing from dark locations or for users of 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. Some sites are located in Greater Phoenix, while other field trips (including some to cooler locations) may best be enjoyed on a 1-day or 2-day Mini-Vacation!

The Sun: The Sun begins September in the constellation of LEO, and moves into VIRGO on September 16th to spend the rest of the month there. On September 22 in the late evening Arizona Time the Sun crosses the Celestial Equator and moves into the celestial Southern Hemisphere.  This event marks the Fall (or Autumnal) Equinox — the beginning of the season of Autumn (Fall).  On September 22nd our days and nights will be of equal length.  Due to the late evening beginning of Autumn, observers can note the Sun sets due West on the 22nd and rises very nearly due East on both the 22nd and the 23rd.

NOT VISIBLE FROM ARIZONA is an Annular Eclipse of the Sun during the early morning hours of September 22nd, when the Sun has not yet risen in Arizona. (The event will likely be broadcast over the Internet, with excerpts shown on television.)  Since the Moon then is too far from the Earth to completely cover the Sun, part of the Sun’s surface will still be visible and the Sun’s pearly-colored Corona (outer atmosphere) can NOT be seen. Annular eclipses are not of interest to astronomers, but can be very interesting to watch, as the sky begins to darken as the Moon nearly covers the Sun.

The next Solar Eclipse visible from Arizona (also an annular eclipse) will occur in 2012. The next Total Solar Eclipse visible from within the Continental USA does not occur until 2017.

The Moon:
September’s FULL MOON occurs near noontime on September 7th in AQUARIUS. The Full Moon rises about twenty minutes after sunset that evening.
The 3rd QUARTER Moon occurs on September 14th in TAURUS.
September’s NEW MOON occurs on the morning of the 22nd in Virgo.
The 1st QUARTER MOON is seen on September 30th in SAGITTARIUS.

NOT VISIBLE FROM ARIZONA is a very small partial eclipse of the Moon which occurs during the afternoon of September 7th, when the Moon has not yet risen in Arizona. Only a few percent of the Moon will even move into the Earth’s shadow, so it would not be a very spectacular sight even if we could view this event outdoors. The next Lunar Eclipse to be visible from Arizona will occur in the early morning hours of August 28th, 2007. That will be a total lunar eclipse and quite spectacular to view “live” outdoors.

In September the Moon passes near three naked-eye planets:
SATURN: Before dawn on the mornings of the 18th and 19th.
VENUS: A thin crescent Moon rises near Venus ½ hour before sunrise on the 21st.
JUPITER: Low in the West the evenings of September 25th and 26th in LIBRA.

The Moon also passes near these prominent stars:
Pleiades star cluster in Taurus the morning of the 12th.
Castor & Pollux in GEMINI the mornings of the 16th and 17th.
Regulus in LEO the morning of the 19th
Antares in SCORPIO the evening of the 27th.

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.  Mars and Jupiter.
MARS is nearly on the opposite side of the Sun from Earth and never visible in a dark sky during September. We MAY see it very low in the West since it begins the month about 10-degrees above the horizon at sunset (sets at 7:40p.m., about 50 minutes after the Sun). By mid-month, it will be impossible to find the red planet even with binoculars. Mars will reappear as a morning planet in the dawn sky and might be spotted by mid-December by sharp-eyed observers.

MERCURY is also on the far side of the Sun on September 1st, but quickly moves Eastward to become visible low in the Southwest during the 2nd half of the month. Mercury then never appears much higher in the sky throughout September, but will move farther from the Sun and gradually appears in a darker sky by month-end.

Observing Challenge: On September 15th, Mars and Mercury lie closer than a Moon’s-width apart as they set together shortly after sunset. Use binoculars to look for the two planets near the sunset point 20 minutes after sunset.  Mercury should appear orange in color and much brighter than Mars. Mars should appear fainter and reddish in color.

JUPITER, the 2nd brightest nighttime object after the Moon and Venus, rides low in LIBRA all month.  Jupiter sets about 3 hours after the Sun on the 1st, but only 2 hours after the Sun on the 30th.  On September 9th, Jupiter passes closest to the 3rd magnitude double star Alpha Libri. Between September 30th and October 4th, Jupiter passes close to the stars Nu Libri and SAO159030, events best observed with strong binoculars or a small telescope.

What Else to See?
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 after the 10th of the month, when the Moon is less likely to interfere.  By late September, Scorpio and Sagittarius will set too early in the evening for enjoyable telescopic viewing.

Constellations CYGNUS (AKA the Northern Cross) and LYRA the lyre are High overhead between 8:30 and midnight.  The three brightest stars overhead 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 the Eagle more to the Southeast).

Excellent positioning of northerly parts of the Summer Milky Way in September makes for enjoyable binocular and telescopic viewing. On Moonless nights, try to trace the Milky Way from Sagittarius upwards to the North through OPHIUCHUS, SCUTUM, DELPHINUS, AQUILA, and CYGNUS and CASSIOPEIA.  Along the way star clusters and nebular gas clouds can be seen along in the Milky Way.  Even a small pair of binoculars will reveal a half dozen fuzzy star and gas clouds in these constellations.
(You can download a free online star chart to help with constellation finding.)

As the Moon slowly moves from West to East around the Earth each month, it occasionally occults (or eclipses) background stars.  Two 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 6:05a.m.  Each morning afterward the Sun rises a bit later.  On September 30th, sunrise occurs at 6:25a.m.

Look for the MOON in the morning sky before the 21st.  The Moon lies near both Regulus and Saturn in Leo on the morning of the 19th.

Morning Planets:  Saturn and Venus.
VENUS is not positioned well for observing in September as it is on the far side of the Sun and very nearly in line with it. Venus begins September very low in the dawn sky in Leo but will be impossible to observe by month end as it continues to move closer to the Sun. Venus reappears at dusk as an evening planet in December.

On the mornings of September 5th and 6th, Venus will be seen close to Regulus, the brightest star in Leo.

Another observing challenge will be to spy the Moon a bit South of Venus VERY low in the East about 5:40a.m. on the morning of September 21st.  Use binoculars for this event!

SATURN  rises in a dark sky on the 1st at 4:22a.m. and rapidly moves Westward away from the Sun.  At month end, Saturn rises at 2:45a.m., more than 3 ½ hours before the Sun.

What Else to See?   The Northern part of the Summer Milky Way makes for excellent viewing after midnight.  It is also cooler in the wee hours, so morning observers should be 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.
(You can download a free online star chart to help with constellation finding.)

The constellation ORION rises by midnight at the end of the month and 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. (See NASA photo of the Orion Nebula to the left.)

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!