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Mercury best for Southern Hemisphere now

2015-sept-4-mercury-spica-night-sky-chart

Tonight is Sep 05, 2015

Moon Phase Courtesy U.S. Naval Observatory

Looking for info on the September 4-5 lunar occultation of Aldebaran? Click here.

On September 4, 2015, the sun’s innermost planet Mercury swings to its greatest evening elongation (27o east of the setting sun). So is this a good time to see Mercury? Yes, if you’re in the Southern Hemisphere. This greatest elongation comes in the same month as the September equinox. That means the ecliptic – or path of the sun, moon and planets – makes a narrow angle with respect to the evening horizon for us in the Northern Hemisphere, but a steep angle for our fellow skywatchers on the southern part of Earth’s globe. That means a grand evening apparition of Mercury for the Southern Hemisphere – and poor one for the Northern Hemisphere.

No matter where you are, Mercury is seen below the star Spica, the brightest star in the constellation Virgo the Maiden.

Mercury is slightly brighter than Spica and takes stage in the same binocular field of view for several days, centered around September 20.

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An inferior planet - a planet that orbits the sun inside of Earth's orbit - appears in the evening sky at its greatest eastern elongation, and in the morning sky at its greatest western elongation. The two inferior planets are Mercury and Venus, residing at a distance of  0.387 and 0.723 astronomical units from the sun, respectively.

An inferior planet – a planet that orbits the sun inside of Earth’s orbit – appears in the evening sky at its greatest eastern elongation, and in the morning sky at its greatest western elongation. The two inferior planets are Mercury and Venus, residing at a distance of 0.387 and 0.723 astronomical units from the sun, respectively.

The most favorable time to see Mercury in the evening sky is when this planet’s greatest eastern (evening) elongation closely coincides with a spring equinox. Because the September equinox is the Southern Hemisphere’s spring equinox, southerly latitudes have a wonderful evening apparition of Mercury throughout this September.

On the other hand, an evening apparition of Mercury is most subdued near an autumn equinox. So we lose out this month, but, never fear, Mercury will put on a good show for us before dawn, beginning in October.

For us in the Northern Hemisphere, there is a consolation prize! Even at mid-northern latitudes, we should be able to catch the planet Saturn in the southwest sky at nightfall. See the chart below.

Recommended almanacs can provide Mercury’s setting time in your sky

Mercury sits too close to the sun's glare and sets too soon after sunset to be seen from northerly latitudes. You might catch the star Spica, however. You should have no trouble seeing the planet Saturn and the star Arcturus.

From the northern part of Earth in September, 2015, Mercury sits too close to the sun’s glare and sets too soon after sunset to be seen easily. You might catch the star Spica, though, and you will have no trouble seeing the planet Saturn and star Arcturus.

Bottom line: Mercury, the innermost planet of the solar system, reaches its greatest evening elongation of 27o east of the setting sun on September 4, 2015. It’s an awesome apparition for the Southern Hemisphere, and a poor one for the Northern Hemisphere. If you get pics, post them at EarthSky Facebook, or submit photos here.

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Astronomy events, star parties, festivals, workshops for September-December, 2015

Super Blood Moon eclipse on night of September 27-28