[News Terms] 'Partial Lunar Eclipse' When the Moon Is Covered by Earth's Shadow

On the 29th, a partial lunar eclipse, where part of the Moon is covered by the Earth's shadow, can be observed.

A lunar eclipse occurs when the Earth is positioned between the Moon and the Sun, causing the Moon to be obscured by the Earth's shadow. The Moon does not disappear completely when it enters the Earth's shadow; rather, part or all of it appears to vanish. It can be seen from anywhere on Earth where it is nighttime.

Partial lunar eclipse that took place from 4:18 PM to 7:47 PM on November 19, 2021. The image shows the process of the eclipse ending from the left side, where the moon is maximally covered by the Earth's shadow at the "maximum eclipse," moving toward the right. Photo by Youngsik Park, senior researcher at the Korea Astronomy and Space Science Institute, taken in Jeju Island. [Photo courtesy of Korea Astronomy and Space Science Institute]

The total lunar eclipse that took place from 5:00 PM to 10:57 PM on November 8, 2022. The moon moves from the right to the upper left. Chief Researcher Youngsik Park of the Korea Astronomy and Space Science Institute captured this in Geumsan, Chungnam. [Photo by Korea Astronomy and Space Science Institute]

The Earth's shadow can be divided into the umbra, the central region where the Sun's light is completely blocked, and the penumbra, the outer region. When the Moon begins to enter the penumbra, a penumbral lunar eclipse starts, during which the Moon's shape remains the same but it becomes slightly darker. A partial lunar eclipse occurs when part of the Moon enters the Earth's umbra, and a total lunar eclipse happens when the entire Moon is covered.

Due to the Moon's orbital motion, a lunar eclipse occurs as the Moon passes through the Earth's shadow from west to east. From the Earth's perspective, the eclipse begins on the left side of the Moon. Sunlight refracted through the Earth's atmosphere reaches the Moon, causing the obscured part of the Moon to appear reddish. The Moon often appears dark red during a total lunar eclipse, which is sometimes called a "Blood Moon."

Because the Earth's shadow is about seven times larger than the Moon, both total and partial lunar eclipses last relatively longer than solar eclipses (which occur when the Moon blocks the Sun). Lunar eclipses happen when the Sun, Earth, and Moon are aligned in a straight line, so the Moon's phase during an eclipse is a full moon. However, since the Moon's orbit is tilted about 5 degrees relative to the Earth's orbit, most full moons do not result in an eclipse.

The Korea Astronomy and Space Science Institute announced on the 23rd that on the 29th at 4:34:30 AM, the partial eclipse will begin as the Earth's shadow starts to cover the Moon, reaching its maximum at 5:14:06 AM, and ending at 5:53:36 AM. The maximum obscuration of the Moon by the Earth's shadow will be 0.127, meaning only about 10% of the Moon's surface area will be covered. Additionally, the Moon's altitude will be about 19 degrees, which is not very high, so it can be observed with the naked eye from locations near the western horizon with an open view. The eclipse will be visible in Korea as well as in Asia, Africa, Europe, Oceania, and the Indian Ocean region.

The next lunar eclipse visible in Korea is expected to occur on September 8, 2025, when the Moon will be completely covered by the Earth's umbra in a total lunar eclipse.

Partial lunar eclipse progression on the 29th. [Source=Korea Astronomy and Space Science Institute]