Reading the Ring Around the Moon
A labeled sequence diagram helps readers explain how the Sun's appearance changes during an annular solar eclipse and recognize what the diagram does not show.
Play the quiz as a gameDuring a solar eclipse, the Moon passes between Earth and the Sun. From some places on Earth, the Moon blocks part or all of the Sun's bright face. The Sun can seem to have a bite missing. Is the Sun changing shape? No. A diagram can help solve that puzzle by separating what we see from what is happening.
An eclipse depends on alignment: the positions of the Sun, Moon, and viewer lining up. The Moon does not make its own light. In an eclipse, its dark outline passes across the Sun. The diagram below shows an annular eclipse, in which a narrow ring of sunlight remains visible around the Moon at the middle stage.
Reading the Eclipse Diagram Read this sequence, or series of steps, from left to right. Each letter marks one stage seen from the same place on Earth. The symbols are simplified views, not photographs. White areas represent visible sunlight. Black areas represent the Moon blocking sunlight. Circle outlines mark the Sun's edge.
A ○ → B ◐ → C ◉ → D ◑ → E ○ Key: A and E, full bright disk; B, left side blocked; C, dark center with bright ring; D, right side blocked. Caption: Five stages of one annular eclipse. The arrows show the order of the views, not how quickly they change.
At A, the Moon has not yet crossed the Sun's edge. At B, it covers the left side of the bright face. At C, it lies in front of the center, but sunlight still outlines it. At D, it covers the right side. By E, it has moved clear. Comparing B with D shows that the dark area changes position as the Moon moves.
Why does C show a ring instead of a completely dark disk? The Moon's distance from Earth changes during its orbit. When it is farther away, its apparent size, or how large it looks, is smaller. If it looks slightly smaller than the Sun during an eclipse, it cannot cover the Sun's whole bright face. The uncovered edge forms the ring.
The drawing answers a question about appearance, but not every question about time. The arrows do not give the interval, or amount of time, between stages. Even though the symbols are spaced evenly, the stages are not necessarily equally far apart in time. A diagram's labels and caption help explain what it can tell us.
To view any stage of an annular eclipse, use undamaged eclipse glasses or a handheld solar viewer that meets the ISO 12312-2 safety standard, with adult guidance. Ordinary sunglasses are not safe for this. The bright ring still requires proper eye protection.