A lunar eclipse is one of the most spectacular events you can watch in the night sky. This event happens when our planet, Earth, passes directly between the Sun and the Moon. It is completely safe to observe, requiring no special eye protection. The eclipse changes the Moon’s appearance, making it seem like it is slowly disappearing or turning a surprising, deep color.
The Earth, Moon, and Sun Line Up
An eclipse occurs when one object in space blocks the light from another. For a lunar eclipse to happen, the Sun, the Earth, and the Moon must line up in that exact order: Sun-Earth-Moon. The Moon normally shines because it reflects the Sun’s light. When the Earth moves into this middle position, our planet casts a large shadow into space, and the Moon passes through it.
The Earth’s shadow causes the Moon to darken during this alignment. This differs from a solar eclipse, where the Moon moves between the Sun and the Earth, blocking the Sun’s light. A lunar eclipse can only happen during the full moon phase. However, because the Moon’s orbit is slightly tilted, this perfect alignment does not occur every month.
The Three Types of Lunar Eclipses
The appearance of a lunar eclipse depends on which part of the Earth’s shadow the Moon travels through. The Earth’s shadow has two main parts: the darker, inner umbra and the lighter, outer penumbra. The umbra is the area where the Sun’s light is completely blocked, creating the deepest shade. The penumbra is the partial shadow where some sunlight still manages to pass around the Earth.
A penumbral lunar eclipse occurs when the Moon only passes through the faint penumbra. This type of eclipse is often subtle, resulting in only a slight dimming of the Moon’s brightness. During a partial lunar eclipse, only a portion of the Moon enters the dark umbra. This creates a noticeable, curved shadow that looks like a bite has been taken out of the Moon.
The most dramatic event is a total lunar eclipse, which happens when the entire Moon moves completely inside the Earth’s dark umbra. Even in this deepest shadow, the Moon does not disappear completely; instead, it takes on a fiery, reddish hue. The phase when the Moon is fully within the umbra is called totality.
Why the Moon Looks Red During an Eclipse
During a total lunar eclipse, the Moon often earns the nickname “Blood Moon” because of its striking reddish color. This appearance is caused by the Earth’s atmosphere acting like a giant lens and filter. Even though the Earth blocks direct sunlight, some light still bends around our planet toward the Moon.
The light that reaches the Moon must first pass through a thick layer of Earth’s atmosphere. Our atmosphere is very good at scattering light with short wavelengths, such as blue and violet. This scattering is the same reason the sky looks blue during the day. The longer-wavelength red and orange light is scattered much less and is able to travel through the atmosphere.
This surviving red light is bent, or refracted, into the Earth’s shadow, illuminating the Moon’s surface. The red light seen on the Moon is essentially a glow made up of every sunrise and sunset happening around the Earth at that moment. The exact shade of red can vary depending on factors like volcanic ash or dust in the Earth’s atmosphere.
How to Watch a Lunar Eclipse
A lunar eclipse is perfectly safe to view directly with your eyes. Unlike a solar eclipse, where special protective glasses are needed, the light from the Moon is never too bright to look at.
To get the best view, check the local time the eclipse is expected to begin and end in your location. Find a spot away from bright city lights to help the darkening Moon stand out clearly against the night sky. While you do not need any special equipment, binoculars can enhance the experience, bringing the Moon’s surface features into sharper focus. Lunar eclipses often last for hours, so finding a comfortable place to sit allows you to watch the full progression of the Earth’s shadow moving across the Moon.