Total Eclipse of the Moon - What is a Lunar Eclipse?
- Brandon Holloman
- Mar 2
- 3 min read
The solar eclipse is the well-known event when the Moon passes between the Earth and Sun, blocking the Sun from view. Less known is the lunar eclipse, where the Earth passes between the Sun and Moon, blocking the light of the Sun that usually reflects off the Moon. The morning of March 3, 2026, at around 3:00 am PST, will provide this special show of celestial alignment.
The Moon periodically orbits around the Earth, taking about a month for its full revolution. When the Moon is on the opposite side of the Earth from the Sun, it’s a bright full Moon, while it’s a dark new Moon if on the same side as the Sun. The Moon doesn’t actually emit light of its own. Instead, its glow comes from the reflection of light from the Sun. So, when the Moon is opposite the Sun, its visible entirety is lit up, but when it’s on the same side, none of it seems lit, as the opposite side of the Moon is receiving all the light instead.
During a usual full moon period, while the Moon may be on the opposite side of the Earth from the Sun, it is at an angle such that the Earth does not block any light. But at least twice a year, and as many as five times a year, the Moon, Sun, and Earth line up such that the Moon ends up in the Earth’s shadow. That is a lunar eclipse. Most lunar eclipses are only partial, where the Moon remains in the Earth’s penumbra and won’t pass the darkest part of the Earth’s umbra, the darkest part of its shadow. But during a total lunar eclipse, such as the March 3 eclipse, the Moon will pass entirely in to the umbra. This alignment is called syzygy.
During a total lunar eclipse, the Moon will take on a dark red color. Some people refer to this as a “blood moon,” although that is not an official terminology. The sanguine glow is due to the scattering and refraction of light through Earth’s atmosphere. The longer wavelengths of light, the red light, are the most resistant to scattering by the atmosphere and will bend around the planet due to the air surrounding Earth and continue on to the Moon, painting it crimson. This is the same process that makes the skies orange and yellow as the Sun sets, as light has to travel through more atmosphere when the Sun is low in the sky, leaving only the scatter-resistant red light, and even after the Sun sets, some light remains due to atmospheric bending. Essentially, the eclipsed Moon is glowing with the light of the sunrise and sunset. If the Earth had no atmosphere, then it would block the light entirely during a total eclipse and leave the Moon invisible.
Lunar eclipses will generally last a total of about six hours, with the total eclipse portion, known as the totality, lasting about an hour and a half. It will start as a penumbral eclipse, where the Moon will dim in brightness over the course of several hours. Then the partial lunar eclipse will begin. During this phase, the Moon will begin to transform into its dark red color and parts of the Moon not completely within the Earth’s shadow yet will glow visibly brighter than the parts in the shadows. Once the Moon is entirely within Earth’s shadow, totality begins. The Moon will be entirely red. Over the following few hours, the Moon will slowly leave the Earth’s shadow and return to its regular color and brightness.
The sight of the Moon turning dim and red would often scare our ancestors. It was considered a bad omen. One can imagine how unnerving the sight can be to an ignorant eye. But knowing the science behind it allows us to appreciate this beautiful spectacle. Make sure to watch it while you have the chance. This will be the final total lunar eclipse until June of 2029.
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