This September, skywatchers are in for a treat with a rare celestial trio: a supermoon, the Harvest Moon, and a partial lunar eclipse all occurring on the same night.
This unique combination promises a striking night sky display visible across much of the globe. Whether you're a casual observer or a dedicated stargazer, this event offers a chance to witness a series of astronomical phenomena all at once, culminating on Tuesday night, September 17, 2024.
What Is a Supermoon?
A supermoon occurs when a full moon coincides with the point in its orbit where it is closest to Earth, known as perigee. This proximity causes the moon to appear larger and brighter in the sky compared to a regular full moon. According to NASA, this supermoon will appear about 7% bigger and 15% brighter than an average full moon, creating a visually spectacular event.
The September 17 supermoon is the second of four consecutive supermoons in 2024, following August’s and preceding the supermoons in October and November. The supermoon effect is subtle but noticeable, particularly when the moon is near the horizon, where its size and brightness are more pronounced due to an optical illusion known as the moon illusion. As NASA explains, "Different publications use slightly different thresholds for deciding when a full moon is close enough to the Earth to qualify as a supermoon," but all agree that the September moon will be larger and more luminous than usual.
The Harvest Moon: A Moon with a Rich Agricultural History
This year’s Harvest Moon is also the full moon closest to the autumnal equinox, which occurs on September 22. The name "Harvest Moon" dates back centuries and was coined because this particular full moon provided crucial light for farmers harvesting their crops late into the evening before the invention of modern lighting.
Historically, farmers relied on the extended moonlight provided by the Harvest Moon to work long hours in the fields. As Alan MacRobert, an editor at Sky & Telescope, explains, "In the days before tractors with headlights, having moonlight to work by was crucial to getting the harvest in quickly before rain caused it to rot." NASA echoes this sentiment, noting that many crops ripen in late summer and early autumn, so the additional light helped farmers maximize their harvest time. The term "Harvest Moon" was first recorded in 1706, and it has remained an important part of agricultural and astronomical traditions ever since.
Partial Lunar Eclipse: A Rare Addition to the Night Sky
Adding to the spectacle is a partial lunar eclipse, which will occur simultaneously with the supermoon and Harvest Moon. A lunar eclipse happens when the Earth passes between the Sun and the Moon, casting a shadow that darkens the moon's surface. Unlike a total lunar eclipse, where the entire moon is shadowed and often takes on a reddish hue, this partial eclipse will see only about 8% of the moon pass through Earth’s shadow.
The partial eclipse will peak at 10:44 p.m. EDT on September 17, when the top section of the moon will be in full shadow. While not as dramatic as a total eclipse, the partial shadowing adds an extra element to the evening's display. The event is a visual reminder of the Earth-Sun-Moon alignment, one of the fundamental celestial dynamics that govern our night sky. According to NASA, this is the second and final lunar eclipse of 2024, following a slight darkening in March.
For those eager to see a total lunar eclipse, the next one visible from the Americas will occur on March 14, 2025.
How to Best View the Event
One of the best aspects of a lunar eclipse is that, unlike a solar eclipse, no special viewing equipment is necessary. Viewers can safely observe the eclipse with the naked eye, though binoculars or telescopes can provide a more detailed view. As the moon slowly dims, the gradual change may seem imperceptible at first, but over several hours, the subtle shifting of light becomes more apparent. KaChun Yu, a curator at the Denver Museum of Nature and Science, suggests watching the moon for an extended period to fully appreciate the change. “From one minute to the next, you might not see much happening,” Yu says, “but over the course of the evening, the transformation will be noticeable.”
For those hoping to photograph the event, a camera with a zoom lens will allow you to capture the details of the moon’s surface, particularly as it enters the Earth's shadow. For casual observers, simply stepping outside during the peak of the eclipse will offer a unique view of one of nature’s most beautiful celestial events.