August 19, 2022: This morning Mars, the moon, and Pleiades easily fit into a binocular field of view. This is a rare, compact gathering. Look for it high in the southeast during morning twilight.
by Jeffrey L. Hunt
This morning, a rare gathering of Mars, the moon, and the Pleiades star cluster is visible. The morning bunching spans 5.6° from the brightest star in the cluster, Alcyone also known as Eta Tauri, to Mars. They easily fit into a binocular field 7.5° across. The gathering does not appear this compact again until June 18, 2058, from the western hemisphere!
An hour before sunrise, look for the moon, nearly two-thirds of the way up in the southeast. Mars is to the lower right and the star cluster is to the upper left. A binocular helps with the view.
It’s reasonable to think that close groupings of these three must occur regularly. Having two of the three together is a frequent occurrence. The moon passes Mars and the Pleiades star cluster each month. Mars is near the Pleiades about every twenty-three months. When the moon passes by, either it is too far away from the Pleiades or Mars is out of range for the trio to fit into a compact gathering.
Further, the moon’s appearance near the Pleiades is confounded by the lunar orb’s moving orbit. The spots where the orbit crosses the solar system’s plane, known as the nodes, slide westward, during a cycle lasting 18.6 years. Sometimes the moon is near the cluster, when it passes by, and other times it is farther away. Gatherings of the trio of objects are infrequent enough to note.
To consider future gatherings, some definitions are needed.
- The target field of view is 7.5°, a typical binocular field.
- The gathering of Mars, the moon, and the Pleiades must be visible to the casual sky watcher either with or without a binocular. Those near the sun, when the sky is too bright to see, are excluded.
- The bunches are visible from the western hemisphere. Other locations have not been considered for this survey.
- The Pleiades is defined by the six brightest stars typically visible to the unaided eye.
- The 7.5° circle is measured from Alcyone, the cluster’s brightest star. Because of this restriction, some stars in the cluster might fall outside the field of view. In comparison, your fist – when your arm is extended – covers about 10° from pinky finger knuckle to your thumb knuckle.
To demonstrate the complexity of seeing a compact gathering, let’s look at the next decade:
July 2, 2024
One hour before sunrise, the crescent moon is 3.7° to the upper right of the star cluster, but Mars is 14.2° to the upper right of the stars. Jupiter is in the region, 4.8° to the upper left of Aldebaran. At this season, twilight is bright at this hour. Use a binocular.
July 30, 2024
One lunar cycle later, the group is higher in the sky. The crescent moon is 7.1° to the lower left of Eta Tauri, but Mars is 4.5° to the lower right of the lunar crescent. The trio does not fit in the binocular field. This nearly meets the criteria. The three fit into a circle, 7.8° apart. Jupiter is still there, 8.1° to the lower left of the crescent.
July 11, 2026
In the eastern sky, one hour before sunrise, the crescent moon is 6.9° to the lower left of the star cluster and 4.0° to the upper left of Mars. The trio fits into a circle 9.5° in diameter.
On the previous lunar cycle during bright twilight – June 13, 2026 – the lunar crescent is 2.0° to the upper right of the star cluster. Mars is over 11° west of the Pleiades.
June 20, 2028
In the eastern sky during very bright morning twilight, the crescent moon is 0.5° to the lower right of the Pleiades – spectacular, but a challenging, sight! Mars is near the horizon, along with Venus. The Red Planet is 9.5° to the lower left of the star cluster.
This bunching occurs near Mars’ solar conjunction and it is not visible with conventional means.
May 10, 2032
With Mars approaching its solar conjunction and low in the west-northwest, 30 minutes after sunset, the trio is challenging to see. They fit within a circle 8.6° in diameter. This is a difficult gathering to spot.
April 20, 2034
This is a beautiful bunching after sunset in the western sky. The trio fits within a circle 8.9° in diameter. Venus is within the view, 5.1° to the lower left of the Pleiades.
June 18, 2058
This is the next date that Mars, the moon, and the Pleiades fit into the binocular field. The fit is snug. One hour before sunrise, the crescent moon is less than 10° up in the east-northeast and 6.3° to the lower left of the star cluster. Mars is 3.0° to the upper right of the moon and 6.0° to the lower left of the Pleiades.
Between the 2034 and 2058 groupings, nearly 20 other gatherings occur. During the June 6, 2043, grouping, in bright twilight, Mercury and Venus are with the trio. The target group is in a circle 8.6° across. Other somewhat compact groupings occur, when the three are in imaginary circles 8° to 10° across.
Mars is at opposition on November 19, 2037, 4.7° from the Pleiades. During this apparition, the planet has a triple conjunction with the star cluster. Mars is near the cluster during four months. The three – Mars, moon, and Pleiades – fit within circles ranging from 8.3° (February 12, 2038) to 10.7° on November 22, 2037.
On July 4, 2041, Venus, Mars, and the Pleiades are in a 6.5° circle, easily within a binocular field of view. When the moon passes through 19 mornings later, Mars moves farther eastward, making the grouping over 11° across. On the previous lunar cycle, the gathering of three is in a circle 9.9° across.
Anytime the moon, especially in the crescent phase, is near the Pleiades, this a spectacular, picturesque scene. Add in a bright planet and we have a one-of-a-kind gathering the three. Mars’ nearly biennial appearance with the star cluster is interesting in its own pattern. The three objects gathered closely together is worth noting. Set an early alarm and take a look!
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