Our sky chart shows the moon and the planet Mercury as they appear in North America, about 35 to 40 minutes after sunset. For the most part, the thin waxing crescent moon and Mercury sit too close to the glare of sunset to be visible from mid-northern latitudes and farther north. These two worlds will be hard to spot after sunset at northerly latitudes, even in binoculars.
People in the Southern Hemisphere should have an easier time catching the young moon and Mercury after sunset on August 27. For example, At Rio de Janeiro, Brazil, Mercury sets about one and one-quarter hours after sunset, and the moon sets about 2 hours after the sun. At Philadelphia, Pennsylvania, on the other hand, Mercury sets less than 45 minutes after the sun, and the moon sets about 50 minutes after sunset.
At sunset in late summer and early autumn, the ecliptic – the pathway of the moon and planets – intersects the horizon at its shallowest angle for the year. So from our northerly latitudes, the young moon and Mercury lurk sideways of the setting sun. Therefore, the young moon and Mercury follow the sun beneath the horizon fairly shortly after sunset at our northerly latitudes.
However, it is now late winter in the Southern Hemisphere. At sunset in late winter and early spring, the ecliptic – the pathway of the moon and planets – intersects the horizon at its steepest angle for the year. So from southerly latitudes, the moon and Mercury hover almost directly over the setting sun. Therefore, the young moon and Mercury stay out till late dusk or nightfall at southerly latitudes.
In the Southern Hemisphere, Mercury will be a fine evening object from now until the end of September 2014. At our northerly latitudes, in stark contrast, there’s a good chance we won’t spot Mercury at all in our September evening sky. The tilt of the ecliptic totally favors the southern climes for Mercury’s present apparition in the evening sky. Mercury will exit the evening sky to enter the evening sky in mid-October. When Mercury reappears in the morning sky in late October, the Northern Hemisphere will then have the advantage.
We expect few, if any, at northerly latitudes to catch the moon and Mercury after sunset on August 27. Even so, there’s an evening treat you won’t want to miss: The bright star Antares plus the planets Mars and Saturn in the southwest sky at nightfall and evening.