Go Stargazing! September Edition

September 6, 2011

Saturn leaves the evening sky in September 2011.  Face west southwest at dusk, and you’ll see Saturn near a star of similar brightness—Spica in Virgo.  Saturn is a bit to the right of Spica as you face southwest.

Each night this month, however, Saturn and Spica appear lower and lower to the horizon, until they set in twilight by mid-month.  When is the last night you can still see it?  Next month, Saturn is behind the Sun and invisible.

A Long Night Falls Over Saturn's Rings
Creative Commons License photo credit: NASA Goddard Photo and Video

Jupiter is now a late evening object.  It rises before 10:45 pm on September 1, and just after 8:30 pm by September 30.  Face east at the appropriate time and look for the brightest thing there—that’ll be Jupiter.   The King of Planets continues to dominate the southwestern pre-dawn sky.  Mars is now a bit higher in the east at dawn.  Although it has brightened, many of the stars in the morning sky outshine it.  However, as it moves from Gemini into dimmer Cancer, Mars is quite identifiable.  Venus was behind the Sun last month, and is still lost in the Sun’s glare.

Io Close-Up with New L8 Jupiter
Creative Commons License photo credit: FlyingSinger

The Big Dipper is beginning to pass under the North Star; Houstonians now need a clear northwestern horizon to see it at dusk.  From its handle, you can ‘arc to Arcturus’ and then ‘speed on to Spica’; those stars set in the west and southwest at dusk.  Antares, brightest star of Scorpius, the Scorpion, is in the southwest, with the ‘teapot’ of Sagittarius to its left.  Meanwhile, the Summer Triangle is virtually overhead.  The stars of summer now dominate the evening sky.  In late evening, you can watch the Great Square of Pegasus rise in the east.  Note that we look towards the center of our galaxy when we face between Scorpius and Sagittarius.  When facing the Great Square or especially south and east of that, we face out of the plane of our galaxy, a direction where there are fewer bright stars.  That’s why the large expanse of sky rising under Pegasus seems devoid of bright stars.

Moon Phases in September 2011:
First Quarter September 4, 12:39 pm
Full September 12, 4:26 pm
Last Quarter September 20, 8:39 am
New September 27, 6:08 pm

Autumnal Equinox

At 4:06 am CDT on Friday, September 23, the Sun is directly overhead at the equator.  This, then, is the autumnal equinox, a date when everyone in the world has the same amount of sunlight.  In the Northern Hemisphere, we’ve seen the days get a little shorter and the midday Sun a little lower each day since June 21.  For us, the season changes from summer to fall at the equinox.

In the Southern Hemisphere, people have seen the days lengthen and the midday Sun get a little higher each day since June.  For them, the season changes from winter to spring.

Rosh Hashanah

The New Moon of September 27 is the one closest to the fall equinox and therefore marks the Jewish New Year.  Rosh Hashanah is not on the New Moon itself but two days later on the 29th, when the slender crescent becomes visible in the west at dusk.

Astronomy Day 2011 at the George Observatory

Come join us anytime from 3 to 10 pm on October 8 for our annual Astronomy Day at the George Observatory. Dozens of telescopes—including our large research telescopes—will be available to give everyone a chance to enjoy the delights of the night sky, including star clusters, planets and galaxies.  Before dusk, we will have solar observing, Expedition Center simulations, outdoor and indoor presentations (beginning at 4) and many other activities!

Authored By James Wooten

James is the Planetarium Astronomer at the Houston Museum of Natural Science. He teaches students every school morning in the planetarium, and also answers astronomy questions from the public.

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