See Mercury at its best morning – Astronomy Now

The innermost planet, Mercury, offers its best exposure of the year in the pre-dawn sky for the remainder of October and through early November. A graphic by Greg Smye-Rumsby.

Mercury is currently visible in the pre-dawn sky as it moves furthest from the Sun on October 25. This apparition (visibility period) gives observers an excellent opportunity to observe the best spectacle on the planet of the year near sunrise. Mercury is by far the most elusive of the bright planets because it never moves too far from our star, whether it appears in the evening sky after sunset, like last May, or like now in the sky of before dawn.

Positions of Mercury and Earth for the period following the lower conjunction of Mercury on October 9, 2021 (noted 1), when the planet is out of sight. The largest aspect ratio in the west of this month (2) is the most favorable morning index for Mercury in 2021. Mercury then passes through an upper conjunction on November 29, 2021 (3), and the largest aspect ratio in is on January 7, 2022 (4).

Mercury is found in the east-southeast sky among the stars of Virgo. From southern England, Mercury is nearly 11 degrees above the horizon at the onset of civil twilight (when the Sun is less than six degrees below the horizon) shortly after 7 hours of the morning (06h00 UT). The planet is at roughly the same elevation for the same degree of twilight across the UK.

The shyness of Mercury is largely explained by its proximity to the horizon, even when it is in the best position. The planet often shines surprisingly brightly, so it can be easy to spot it if you can get a decent view of where it is in the sky. For city dwellers and city dwellers, the view of Mercury can easily be obstructed by trees and buildings.

Mercury shines brightly at magnitude -0.5 at about maximum elongation, when peaking in altitude, and continues to lighten slightly to magnitude -0.8 to -0.9, its maximum brightness at this onset when it is visible in the pre-dawn sky. Of course, atmospheric extinction is a threat so close to the horizon and will take the edge of Mercury’s brightness, just like any low-level fog. Bring a pair of binoculars in case you are planning a trip to observe Mercury.

Thanks to a small telescope, Mercury presents a half-phase like a Moon of the last quarter at the greatest aspect ratio. As it heads west toward an upper conjunction on the other side of the Sun on November 29, Mercury’s phase will swell as its disk gets smaller.

Mercury will exhibit roughly a similar phase on October 27. This image was taken on April 27, 2018, when Mercury sported a 40% illuminated phase and spanned 8.3 inches. Image: Team D. Peach / Chilescope.

Mercury remains visible in the sky before dawn for the first two weeks of November, although after the end of the first week it is only five degrees at the start of civil twilight around 6.30am GMT London.

About Johnnie Gross

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