By: Hannan Mohammed

According to the Planetary Society, we see around two to five solar eclipses every year and about two lunar eclipses each year as well. When these occur, we like to observe and take photos of these phenomena. But what is an eclipse in the first place? And what is the difference between solar and lunar eclipses?

Solar Eclipses

A solar eclipse occurs when the Sun, Moon, and Earth align in such a way that the Moon blocks sunlight from reaching the Earth and casts a shadow over an area of the Earth’s surface. For this to happen, the Moon needs to be perfectly aligned between the Earth and the Sun. But, a total solar eclipse doesn’t occur very frequently because the Moon doesn’t orbit in the same plane as the Earth and the Sun. Instead, it orbits in the ecliptic plane, where it’s tilted by five degrees, and because of this, the Moon’s shadow often misses Earth.

There are only two times a year where a new moon has an opportunity to show a solar eclipse when it crosses the Earth-Sun plane, called ‘eclipse seasons’. When a total solar eclipse happens, the Moon directly blocks most of the Sun. However, the Moon doesn’t completely block the Sun, allowing the Sun’s outer atmosphere—called the corona—to be briefly visible to us on Earth. A partial eclipse occurs when the Moon and the Sun aren’t aligned well enough to show a total eclipse, so only a part of the Sun is blocked.

But what about the shadow that’s cast on Earth’s surface during a solar eclipse? It has two main parts, called the umbra and penumbra. The umbra is the inner shadow, usually around 50 miles wide, and only within it is a total solar eclipse visible. The penumbra, on the other hand, is the outer shadow that can span around 1,000 miles; only a partial eclipse is visible from this area.

The Moon’s shadow traces a path across the Earth’s surface as it continues to orbit our planet, called the eclipse path, and it takes around four to five hours for the Moon’s shadow to fully pass over Earth. Within the eclipse path, the path of the umbra is called the path of totality, and along the path of totality, a total solar eclipse lasts for about a few minutes.

Lunar Eclipses

A lunar eclipse occurs when the Moon is covered by the Earth’s own shadow, preventing sunlight from reaching it. This phenomenon works similarly to how solar eclipses work; when the Earth is positioned between the Sun and Moon and casts its own umbral shadow onto the moon. This doesn’t happen every month for the same reason that total solar eclipses don’t happen frequently: the Moon rotates on its own ecliptical plane, and when it rotates around Earth, it won’t always line up with Earth’s shadow.

However, when it does, we can observe that the Moon becomes a shade of red. Why does the Moon appear to change color? This is due to the Earth’s atmosphere scattering blue light coming from the Sun. As it does so, the edges of the atmosphere reflect a bit of red light onto the Moon’s surface, making it appear red. This is what’s usually called a ‘blood Moon’.

It’s important to note that blood Moons are only seen during a total lunar eclipse; when there’s a partial lunar eclipse, the Moon doesn’t fully pass through the Earth’s umbra, so only parts of the Moon will appear to be red. Lunar eclipses are also much longer than solar eclipses, as a total lunar eclipse can be as long as an hour and 45 minutes.

For more information, please visit:

• https://science.nasa.gov/eclipses/geometry/
• https://www.planetary.org/night-sky/lunar-eclipse