Why do annular eclipses happen?
The Moon’s orbit around the Earth is somewhat elliptical, meaning it is not perfectly circular. This means that the distance between the Earth and the Moon varies throughout the year, making the apparent size of the Moon as seen from Earth vary as well.
Most of the time, the Moon appears large enough to cover the entire Sun during a total solar eclipse. But when the Moon is at its apogee — the point in its orbit farthest from Earth — it appears slightly smaller than the Sun, and cannot cover the Sun completely. When the Moon passes directly in front of the Sun during the Moon’s apogee, it creates an annular eclipse.
What will you see during an annular solar eclipse?
The eclipse begins and ends as a partial eclipse. At the beginning stage, when you look at the Sun (with proper eye protection), you’ll notice a small, dark crescent slowly appearing on one side of the Sun, as though a small bite were being taken out of the Sun. As the Moon continues to move, the Sun will start to look more like a crescent shape, and the daylight will start to dim noticeably. Shadows on the ground might start to look sharper and more defined.
Once the Moon becomes centered over the Sun, you’ll see the Sun’s outer edges form a bright ring around the dark disk of the Moon. This is often referred to as the “ring of fire,” and is technically called the “annulus,” which is where the term “annular” eclipse comes from. While this won’t create the same level of darkness you see during a total solar eclipse, the quality of the daylight will be very different from normal daytime, and may take on an eerie quality. You may also notice some of the same phenomena you’d see during a total eclipse, like changes in temperature and animals behaving differently.
The Moon will then continue its journey across the Sun, causing the ring of fire to gradually narrow until the eclipse transitions back into a partial eclipse and then ends.