The Sky This Month – September 2013

False Dawn

The month of September affords observers with dark sky the chance to see the zodiacal light, a faint wedge of eerie white light from the inner solar system.  Also this month, low in the western sky at sunset, Venus passes the bright star Spica, the Moon, and Saturn as the second week of September gets started.  The planet Mars moves through a famous star cluster in the early morning sky.  And the Sun crosses the celestial equator heading south, marking a changes of seasons.  Here’s what to see in the night sky this month…

 1-15 September.   If you have very dark and clear sky, look for the zodiacal light in the eastern sky before sunrise in the northern hemisphere.  This whitish glowing wedge of light appears to thrust out from the horizon.  The zodiacal light is simply sunlight reflected off tiny dust particles in the inner solar system.  For observers in the southern hemisphere, it is best seen later this month and next in the western sky after sunset.

6 Sept.  The bright star Spica comes within 2º of brighter Venus in the southwestern sky after sunset.

8 Sept.  Venus passes very close to a slender crescent Moon in the southwestern sky at dusk.  The Moon passes in front of Venus near sunset for observers in parts of Brazil, Argentina, Uruguay, and Chile.  Venus remains low in the western sky because of the shallow inclination of the ecliptic this time of year in the northern hemisphere.  The planet is still very bright at magnitude -4.0, but you have to look a little lower to the horizon to see it.


8-9 Sept.  Mars passes through the Beehive star cluster (M44) in the constellation Cancer in the early morning hours.  Use binoculars or telescope at low magnification for the best view of the red-orange planet.

9 Sept.  Saturn, Venus, and the crescent Moon congregate in the western sky after sunset.  Low in the southwest after sunset, Saturn is past its prime this year for telescopic observation, but its rings remain visible in a small telescope.

12 Sept.  First Quarter Moon,  17:08 UT

17 Sept.  Saturn and brighter Venus come within 4° of each other in the evening sky

19 Sept.  Full Moon,  11:13 UT

22 Sept.  At 20:44 GMT, the Sun passes the celestial equator moving south.  The marks the first day of autumn in the northern hemisphere and the first day of spring in the south.

24-30 Sept.  Mercury lies very low in the west-southwestern sky 30 minutes after sunset.  On Sept. 24, it comes within 3/4 of a degree of Spica.

27 Sept.  Last Quarter Moon,  3:55 UT

30 Sept.  Brilliant Jupiter is well up by dawn.  The planet is the brightest object in the sky at this hour except for the Moon.  It comes within 0.5° of the 3rd-magnitude star Wasat (δ Geminorum) in the constellation Gemini by month’s end.