Catch Mercury at Its Morning Best Next Week

On August 19, Mercury will reach greatest elongation west, offering early risers in Ireland one of the best opportunities of the year to see the elusive planet.

Greatest elongation west occurs when Mercury is at its furthest apparent distance from the Sun in the morning sky. At this point, the planet rises before dawn and can be seen low in the east before sunrise. By contrast, greatest elongation east happens when Mercury is farthest from the Sun in the evening sky, becoming visible after sunset.

In the weeks between these two points, Mercury’s quick orbit around the Sun carries it either behind the Sun from Earth’s point of view, known as superior conjunction, or directly in front of it, known as inferior conjunction. Because Mercury never strays far from the Sun, its visibility is always limited to short periods before sunrise or after sunset.

At this month’s greatest elongation west, Mercury will be shining brightly against the backdrop of early morning twilight. For the best view, find an unobstructed horizon toward the east and start looking about 45 minutes before sunrise. Binoculars can help locate the planet if the sky is hazy or if there is lingering cloud.

Mercury’s appearance in the morning sky is always fleeting, as it will begin sinking back toward the Sun within days of elongation. Observers who miss it this time will need to wait for the next morning apparition later in the year.