What Causes a Solar Eclipse?

A solar eclipse is a natural phenomenon that occurs when the Moon temporarily blocks the Sun’s light, casting a shadow on Earth. The science behind a solar eclipse is just as fascinating as the event itself. In this article, we’ll explain how solar eclipses occur, why they don’t happen every month, and what causes the different types of solar eclipses.

What Is a Solar Eclipse?

A solar eclipse occurs when the moon passes between the Earth and the sun, aligning perfectly to block all or part of the sun’s light. For a short period, the day becomes dimmer, the temperature may drop, and a dramatic shadow moves across the surface of the Earth. Depending on how the sun, Earth and moon align, different types of solar eclipses can occur: total, partial, annular, and hybrid. The type of eclipse you experience depends on your location on Earth and how close the moon is to the sun at the time.

The type of eclipse you experience depends on your location on Earth, the alignment of the Sun, Moon and Earth, and the Moon’s distance from Earth.

How Does a Solar Eclipse Happen?

A solar eclipse occurs due to the particular alignment of the Earth, moon, and sun. To understand this alignment, it’s essential to know a few key facts about the orbits of the moon and Earth.

The moon orbits the Earth approximately once every 29.5 days, a cycle known as a lunar month. If you’re curious about how scientists forecast these celestial events, read more about how solar eclipses are predicted.

The Earth orbits the sun once a year.

For a solar eclipse to occur, the moon must be in its new moon phase, which means it is located directly between the Earth and the sun.

However, solar eclipses do not occur every month. That’s because the moon’s orbit is slightly tilted—about 5 degrees—relative to the Earth’s orbit around the sun. The moon usually passes slightly above or below the sun when it’s in the new moon phase. But when the orbits align just right, the moon passes directly before the sun, and a solar eclipse occurs.

Why Is a Solar Eclipse So Rare?

Although the moon orbits the Earth every month, solar eclipses are rare because the necessary conditions for alignment don’t happen often. The moon’s orbit is inclined relative to Earth’s orbit around the sun, so the moon’s shadow usually misses Earth.

For a solar eclipse to occur, the moon must cross the ecliptic plane, which is the plane of Earth’s orbit around the sun. This only happens during specific times of the year, known as eclipse seasons. There are usually two eclipse seasons per year, and during each season, the potential for both a solar and a lunar eclipse exists.

Even when a solar eclipse does occur, it may only be visible from specific locations on Earth. The shadow cast by the Moon during a total eclipse can be relatively narrow, often only a couple hundred kilometres wide, so only a tiny area of the Earth will experience totality. Outside this narrow path, observers will see a partial eclipse.

For a detailed comparison between solar and lunar eclipses, explore our guide on solar vs lunar eclipse.

Different Types of Solar Eclipses

There are several types of solar eclipses, each caused by slightly different alignments of the sun, moon, and Earth:

Total Solar Eclipse

In a total solar eclipse, the moon completely covers the sun, blocking its light and creating a brief period of twilight during the day. This type of eclipse is rare and can only be seen within the narrow path of totality, where the moon’s umbra touches Earth. Outside this path, observers will only see a partial eclipse.

Partial Solar Eclipse

In a partial solar eclipse, only part of the sun is obscured by the moon. This type of eclipse is more common and can be seen from a broader area. However, it lacks the dramatic effects of a total solar eclipse, such as the appearance of the sun’s corona.

Annular Solar Eclipse

An annular eclipse occurs when the moon is farther from Earth in its elliptical orbit, appearing smaller in the sky. As a result, the moon doesn’t completely cover the sun, and a ring of sunlight—often called the ring of fire—remains visible around the moon.

Hybrid Solar Eclipse

A hybrid eclipse is a rare combination of a total and an annular eclipse. In some parts of the eclipse’s path, the event will appear as a total eclipse, while in others, it will be seen as an annular eclipse.

Solar Eclipses in Iceland

Whether a solar eclipse can be seen from Iceland depends on the path of each individual eclipse. The August 12, 2026 total solar eclipse provides a recent example, with the path of totality crossing western Iceland, including Reykjavík, Snæfellsnes, the Westfjords and parts of the Reykjanes Peninsula.

In Reykjavík, cloud cover obscured the Sun during much of the event, but the city still experienced the dramatic change in light caused by totality. The sky gradually darkened before Reykjavík became completely dark for around one minute and daylight returned.

Perlan’s elevated location on Öskjuhlíð offers panoramic views across Reykjavík and the surrounding landscape. Visitors can also learn about Icelandic nature through exhibitions covering volcanoes, glaciers, the northern lights and other natural phenomena.

Read more about what happened during the 2026 total solar eclipse in Iceland.