• Here at mid-northern latitudes, we'll have to be on the sharp lookout to catch the waxing crescent moon and planets Mars and Saturn after sunset on September 18, 2012. They'll be low in the southwest sky at dusk, and perhaps visible to the unaided eye around an hour after the sun goes down. An unobstructed western horizon in the direction of sunset is essential if you want to witness this gathering of celestial bodies in the evening twilight from latitudes like those in the U.S. or Europe. If you have binoculars, bring them along.
• This is September 17's sky chart, showing a Southern Hemisphere sky at

sunset. By September 18, the moon will be higher in the sky. In the Southern Hemisphere, the steepness of the ecliptic causes the moon and planets to stay out longer after sunset and to be more easily visible.
• On the other hand, if you live in the Southern Hemisphere or at tropical latitudes in the Northern Hemisphere, it's a different story altogether. The moon, Mars, Saturn - and also the star Spica - won't set until after dark from Earth's more southerly latitudes. We at mid-northern latitudes are very unlikely to see the star Spica, for example. But - further south on Earth's globe - Spica will be visible near the western horizon after sunset.
• The farther south you live on Earth's globe, the longer Mars, Saturn and Spica stay out after nightfall. By the way, you can distinguish these orbs in a dark sky by

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