What is a supermoon?

Why does a supermoon happen?

The moon does not orbit the Earth in a perfect circle; its path is an ellipse, an elongated oval shape. Because of this, the distance between the Earth and the moon constantly changes throughout the month. The point in the orbit where the moon is closest to Earth is called the perigee, while the point farthest away is known as the apogee.

A supermoon happens when a full moon phase occurs at or near the perigee. Because the moon is physically closer to our planet at this time, it subtends a larger angle in the sky, appearing up to 14 percent larger and 30 percent brighter than a full moon at apogee. This optical effect is most noticeable when the moon is near the horizon, a phenomenon often enhanced by the "moon illusion," where the brain compares the moon to distant foreground objects.

How to view a supermoon effectively

Observing a supermoon requires no special equipment, as the event is easily visible to the naked eye. However, timing and location can significantly impact your experience. Because the moon appears largest when it is low on the horizon, the best time to view it is during moonrise or moonset.

To maximize your viewing experience, follow these guidelines:

• Check a local lunar calendar to confirm the exact date and time of the moonrise in your specific time zone.
• Choose a location with a clear, unobstructed view of the eastern horizon for moonrise or the western horizon for moonset.
• Avoid areas with heavy light pollution if you want to see the moon’s surface brightness contrast against the sky.
• Use a mobile app to track the moon's path across the sky to ensure you are positioned correctly before the event begins.

What is the difference between a supermoon and a regular moon?

To the casual observer, the difference between a supermoon and a standard full moon is subtle. While the technical increase in size and brightness is measurable by astronomers, the human eye often struggles to detect the change without a direct side-by-side comparison. The moon's distance at perigee is roughly 226,000 miles, compared to about 252,000 miles at apogee.

The primary distinction is the intensity of the moonlight. During a supermoon, the increased surface area and proximity result in a slightly higher albedo, or reflectivity, causing the landscape to appear more illuminated. This is particularly striking in rural areas away from artificial city lights. Even though the difference is incremental, the event serves as a valuable opportunity for public engagement with astronomy and the mechanics of our solar system.

Common mistakes when photographing a supermoon

Many amateur photographers struggle to capture the scale of a supermoon, often ending up with images where the moon appears as a tiny, washed-out white dot. A common error is using a wide-angle lens, which makes the moon look significantly smaller than it appears to the human eye. To capture the moon properly, you need a telephoto lens with a focal length of at least 200mm or higher.

Follow these technical steps for better results:

1. Use a sturdy tripod to eliminate camera shake, as even minor vibrations will blur the image at high zoom levels.
2. Set your camera to manual mode and keep your ISO low to avoid digital noise.
3. Use a fast shutter speed to compensate for the moon's movement across the sky, which is faster than most beginners realize.
4. Focus manually on the moon’s craters rather than relying on autofocus, which may struggle with the high contrast of the lunar surface.

How often do supermoons occur?

Supermoons are not rare events; they typically occur three to four times per year in consecutive months. This happens because the moon’s orbit and the lunar cycle are not perfectly synchronized, allowing the perigee to align with the full moon phase several times in a row before the cycle drifts. Occasionally, there may be a year with no supermoons, or conversely, a year with five.

Because the definition of a supermoon is not strictly defined by a single distance threshold, different astronomical organizations may occasionally disagree on whether a specific full moon qualifies. Generally, if a full moon occurs within 90 percent of its closest approach to Earth, it is classified as a supermoon. This loose definition ensures that the public has multiple opportunities throughout the year to observe the moon at its most impressive, keeping interest in lunar cycles high across the globe.