Mercury is honoured again in September

After observing Mercury transit in front of the Sun’s surface last May 9, why not try your hand at spotting the planet early in the morning, before sunrise? It’s the best opportunity this year to do it.

Mercury is generally difficult to see due to its proximity to the Sun, but at month’s end the tiny planet manages to distance itself appreciably from the Sun’s glare. In fact, from September 23 to the first week of October, astronomers in the Northern Hemisphere will enjoy the best morning window for observing Mercury in 2016. .

Begin setting up between 6:00 and 6:30 a.m. (30 to 60 minutes before sunrise) and be prepared to see Mercury for one last time this year. The constellation of Leo, which seems to rear above the eastern horizon at dawn, will indicate where to look. At the beginning of this favourable window Mercury is faint, but it brightens substantially over the last few mornings of September, which will make it easier to find without the use of binoculars.

Spotting the planet will still be a challenge, since no other bright celestial object will appear close to it, with the exception of the Moon on September 29: On that morning, a thin lunar crescent will appear suspended just one degree beneath the tiny planet. Since Mercury will lie less than 10 degrees from the horizon, the skyline must be absolutely clear.

Saturn and Mars at twilight

This September, Saturn and Mars are visible at day’s end in the south-southwest, right above Scorpius. Their low position in the sky will necessitate an unobstructed horizon, so be mindful when selecting an observing location!

In fact, these two planets will be the “stars” of the autumn sky, and they are still superb to view in a telescope. Saturn’s rings are almost at their maximum inclination toward Earth and are readily observable. As for Mars, although it is now much farther than during its May opposition, which makes details difficult to distinguish, the planet’s reddish-orange tint is always impressive. The first quarter moon will accompany the planetary duo on the evenings of September 8 and 9.

This month Venus will also be accessible, just after sunset, if your western skyline is completely clear: The dazzling planet will linger within 10 degrees of the horizon. Fortunately, its striking brilliance will make it relatively easy to find—at least, easier than spotting Mercury in the morning sky. A thin crescent moon will appear near Venus on the evening of September 3.  

Invisible eclipses

Although they won’t be seen in Quebec, it’s interesting to note that two eclipses will occur this month.

First, an annular solar eclipse will take place on September 1. The Moon, still a few days away from its September 6 apogee, will be too far to completely hide the Sun; during the eclipse maximum, visible from Tanzania, 95 percent of the solar disk will be masked. This annular eclipse takes place along a narrow corridor, 13 400 km long, which stretches from the Atlantic to the Indian Ocean, and will impact Gabon, both Congos, Tanzania, Mozambique, Madagascar and Reunion. Nearly all the rest of the African continent will witness a partial eclipse.

Then, a penumbral lunar eclipse follows on September 16. During the event’s maximum, the northern part of the Moon will exhibit a grey cast, which won’t be visually remarkable.  This eclipse will be seen from Europe, Africa and Asia.

In closing, autumn begins in the Northern Hemisphere on the morning of Thursday, September 22, at 10:21 EDT. Apple picking season and the pumpkin harvest are on their way.

Clear skies!