An annular eclipse occurs when the Moon is in line with the Earth and the Sun but is relatively farther away from the Earth in its orbit. As a result, the apparent size of the Moon appears smaller than the Sun, and it does not fully cover the Sun's disk. Instead, during an annular eclipse, a bright ring or annulus of the Sun's disk remains visible around the Moon.
The reason for this lies in the varying distances and sizes of the Earth, Moon, and Sun. The Moon orbits the Earth in an elliptical path, which means its distance from the Earth varies during its orbit. When the Moon is closer to the Earth (at its perigee), it appears larger in the sky, and if it aligns perfectly with the Sun and Earth, it can fully cover the Sun's disk, leading to a total solar eclipse.
However, when the Moon is at its apogee, the farthest point in its orbit from the Earth, it appears smaller in the sky. If this happens during an alignment with the Sun and Earth, the Moon cannot completely block out the Sun, resulting in an annular eclipse.
It's important to note that the Moon's orbit is not perfectly circular, and its distance from Earth can vary. This is why we observe both total and annular solar eclipses, as well as partial eclipses, depending on the specific alignment of the Sun, Moon, and Earth at the time of the event.