What is a lunar eclipse?

When thinking about a lunar eclipse, it's essential to start with understanding Earth's shadow. Our planet casts two types of shadows into space: the umbra and penumbra.

The umbra is the innermost and darkest part of the shadow where the light from the Sun is completely blocked by Earth. If you were standing in the umbra during an eclipse, you'd witness what we call totality – a complete coverage of the Sun's light. On the other hand, the penumbra is a lighter shadow where the light is only partially blocked. Being in the penumbra during an eclipse means you'd see the Sun partially obscured.

During a lunar eclipse, the Moon travels through these shadows, creating the spectacular celestial events we witness from Earth. To visualize this, imagine a line-up with the Sun on one end, followed by Earth in the middle, and then the Moon. As the Moon orbits our planet, there will be times when it passes behind Earth, entering either the umbra or penumbra, leading to different kinds of lunar eclipses.

A total lunar eclipse is a breathtaking sight and occurs when the Moon enters the Earth's umbra completely. As it moves into this dark shadow, the Moon darkens significantly but doesn't go pitch black. Instead, it often glows with a reddish color, which is why a total lunar eclipse is sometimes fondly referred to as a 'blood moon.'

This phenomenon is caused by the Earth's atmosphere acting like a lens that refracts, or bends, sunlight. The atmosphere filters out shorter blue wavelengths and allows longer red wavelengths to pass through, casting a sunset-hued shadow on the Moon. The exact color of the blood moon can vary from one eclipse to another, depending on atmospheric conditions such as dust or volcanic ash.

A total lunar eclipse is also the only time you can indirectly see Earth's atmosphere from space, as the red ring around the planet is essentially all the world's sunrises and sunsets happening simultaneously!

In a partial lunar eclipse, as the name suggests, only a part of the Moon travels through the darkest shadow of Earth - the umbra. Unlike a total eclipse, the alignment isn't perfect, so only a section of the Moon is shadowed, while the rest continues to reflect sunlight as usual.

Distinguishing between different stages of a partial eclipse can be quite a treat for the avid skywatcher. The shadowed portion can range from a small nibble out of the Moon to almost total coverage. This graduated shading creates a stunning visual effect as one can clearly observe the curved edge of Earth's shadow moving across the lunar surface.

A partial lunar eclipse is more common than a total eclipse and serves as a fascinating demonstration of the celestial mechanics at play in our solar system. Observers can watch as the Moon slowly drifts into Earth's shadow and then back out, gaining insight into the orbital dance of these celestial bodies.

The most subtle of lunar eclipses is the penumbral lunar eclipse. It occurs when the Moon passes through only the Earth's penumbra, the faint outer shadow. The changes in luminosity are so light that they can be hard to detect without a telescope or, sometimes, any equipment at all.

During a penumbral eclipse, the Moon's brightness will gently decrease, and you might notice a slight shading on one side—but no distinct Earth shadow like in partial or total eclipses. The difference in brightness is usually only discernible by comparing photos of the Moon before and during the eclipse.

Penumbral eclipses happen more frequently than partial or total eclipses but are less dramatic. Still, they provide an excellent opportunity for beginners to practice observing and photographing lunar phenomena, as well as understanding the complex interplay of the Earth, Sun, and Moon.