09/12/2016 – Ephemeris – Mercury passes inferior conjunction with the Sun today
Ephemeris for Monday, September 12th. The Sun will rise at 7:18. It’ll be up for 12 hours and 39 minutes, setting at 7:58. The Moon, 3 days past first quarter, will set at 3:34 tomorrow morning.
Today the Planet Mercury will pass inferior conjunction, that is move between the Earth and the Sun. Unlike last inferior conjunction, when it passed directly in front of the Sun on May 9th. This time it will pass below the Sun. The term inferior means it is between the Earth and the Sun. A superior conjunction is when Mercury passes the back side of the Sun. Mercury will be moving into the morning side of the sky, and toward the end of the month it will be much easier to spot than it was last month when it was low in the west. On autumn mornings the ecliptic, the path of the Sun and planets, sticks up, close to vertical, while in the evenings it lies close to the horizon, which is also why Venus sets so soon after the Sun now.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Note in the charts above and below the line passing through the Sun, and the one the planets hang around is the ecliptic, the projection of the Earth’s orbit on the celestial sphere. The grid line running through the west compass point at the horizon is the celestial equator. I’m allowing us to see below the horizon. As planets rise, move across the sky and set they will appear to move parallel to the celestial equator.
Note too that Mercury appears farther from the Sun on August 16th than at September 28th. And it is. On August 16th Mercury appears 27.4 degrees from the Sun. On September 28th, it’s only 17.8 degrees. That’s a big advantage for observers in the southern hemisphere. The best times to see an eastern elongation of Mercury is on winter and spring evenings, and the best times to see a western elongation of Mercury is on summer and autumn mornings. Since the seasons are reversed from the northern hemisphere to the southern hemisphere. Our not so good August 16th elongation of Mercury was a really good one for folks south of the equator. We’ll return the favor September 28th. But the best southern hemisphere greatest elongations are always greater in the separation of Mercury from the Sun than northern ones because Mercury has a markedly elliptical orbit.