November 3, 2021: Before sunrise speedy planet Mercury, the crescent moon, and the star Spica are grouped together. The trio does not appear this close together again until 2033.
by Jeffrey L. Hunt
Not until September 25, 2033, will Mercury, the crescent moon, and the star Spica fit into the same binocular field.
This morning the triplet is visible before sunrise. About 45 minutes before sunup, find a clear horizon to the east-southeast.
There you’ll see the moon’s thin sliver, only 3% illuminated, about 10° above the horizon. Mercury is bright, 3.5° below the moon. A binocular helps.
Once the crescent moon and Mercury are in the field of view, move the binocular slightly so they appear to the left portion of the field. Spica is visible 4.4° to the right of Mercury. The trio is in the field of view.
Mercury passes Spica every year, usually from late September to early November, depending on its location compared to the sun, as the planet pivots through its solar orbit. The planet is observable in the morning sky or the evening sky.
Groupings that occur during October are impossible to view under normal circumstances. Spica is in the sky with the sun. The star passes through its solar conjunction and it is not visible during darker twilight, either after sunset or before sunrise.
Mercury and Spica do not appear together in a dark sky because the speedy planet does not venture far from the sun. Mercury is not visible after the end of evening twilight or before the beginning of morning twilight. On the other hand, Spica is visible at various nighttime hours during the year.
The window to see Mercury and Spica together is limited to small segments of time when it is low in the eastern sky before sunrise or in the west after sundown. Even though the moon passes Mercury and Spica each month, adding it to the infrequent grouping of the other two objects makes this trio an infrequent occurrence.
During the twelve years until the next time the trio fits into the same binocular field and they are observable in either the evening or morning sky, there are some close groupings.
On September 21, 2027, Mercury and Spica are over 9° apart when the evening crescent moon is 2.5° below Mercury. Additionally, this is a challenging observation that occurs during bright twilight.
The following year, Mercury and the crescent moon are over 11° apart when near Spica.
Other closer groupings occur, but these are during the daytime, not easily observed or the moon is not near Spica, when Mercury is within a binocular’s field of view of Spica.
Take this opportunity to spot this infrequent grouping of Mercury, Moon, and Spica.
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