During a solar eclipse, the variation in colors visible on the edge of the shadow (known as the penumbra) and the light (known as the umbra) is primarily due to a phenomenon called "Baily's beads" or "the diamond ring effect." This effect occurs when the Moon partially covers the Sun, creating a narrow crescent-shaped region where sunlight can pass through.
Baily's beads are caused by the irregularities and mountains on the Moon's surface. As the Moon moves in front of the Sun, the sunlight passes through the valleys between the lunar mountains, creating bright spots of light. These bright spots are known as Baily's beads because they resemble a string of bright beads around the edge of the Moon. The effect is named after Francis Baily, an English astronomer who first described it in 1836.
The colors visible on the edge of the shadow and light during a solar eclipse are a result of the Earth's atmosphere. The Earth's atmosphere scatters sunlight, causing different colors (wavelengths) of light to scatter to different extents. This phenomenon is known as Rayleigh scattering. The shorter wavelengths of light, such as blue and violet, scatter more than the longer wavelengths, such as red and orange.
As a result, when the sunlight passes through the Earth's atmosphere and reaches the region of the penumbra during an eclipse, the blue and violet wavelengths tend to scatter more, making the edge of the shadow appear bluish or purplish. On the other hand, the longer wavelengths, such as red and orange, are less scattered and can reach the umbra, creating a reddish or orange glow along the edge of the light.
The exact colors and their intensities can vary depending on various factors, including the composition and density of the Earth's atmosphere at different locations, as well as the atmospheric conditions during the eclipse. Additionally, the colors can be influenced by other factors such as the presence of dust or pollutants in the atmosphere.
It's worth noting that the specific colors observed during an eclipse can also be affected by the type of solar filter or protective eyewear used to view the event. These filters can affect the color perception and intensity of the light reaching the observer's eyes.