A solar eclipse happens when the Moon passes between the Earth and the Sun, blocking all or part of the Sun’s light from reaching us. It’s a cosmic lineup that depends on the orbits of these three bodies.
The Earth orbits the Sun, and the Moon orbits the Earth. These orbits aren’t perfectly circular, and they’re tilted relative to each other. The Moon’s orbit is inclined about 5 degrees to the Earth’s orbit around the Sun, called the ecliptic. This tilt means the Moon usually passes above or below the Sun from our perspective, so we don’t get an eclipse every month. But when the timing and alignment are just right—specifically, when the Moon is near one of its orbital nodes (where its path crosses the ecliptic) and it’s at new moon phase—it can cast a shadow on Earth, creating a solar eclipse.
There are a few types. A total solar eclipse occurs when the Moon completely covers the Sun, revealing the Sun’s outer atmosphere, the corona. This only happens along a narrow path on Earth where the Moon’s dark central shadow, the umbra, falls. Outside that path, in the partial shadow or penumbra, you’d see a partial eclipse, where the Sun looks like a crescent. An annular eclipse happens when the Moon is farther from Earth in its elliptical orbit, appearing smaller and leaving a ring of sunlight visible around its edges, often called a “ring of fire.”
The geometry is precise. The Sun is about 400 times larger than the Moon but also 400 times farther away, making them appear roughly the same size in our sky. That’s why the Moon can cover the Sun so neatly during a total eclipse. The whole event unfolds because the Moon’s shadow moves across Earth’s surface as it orbits, with totality lasting just a few minutes at any one spot.
