The antumbra shadow is the only area of a shadow responsible for just one type of eclipse, namely the annular solar eclipse. The other two types of shadows, the umbra, and antumbra create three different types of eclipses.
The antumbra is the lighter part of a shadow, similar to the penumbra; however, it forms at a certain distance from the object casting the shadow. Let’s see exactly what an antumbra shadow is and how it creates annular solar eclipses.
The Antumbra Shadow
Any opaque object illuminated by a light source will create a shadow into space. This shadow has three different areas, the umbra, antumbra, and penumbra.
The umbra is the darkest and central part of the shadow. The antumbra is the lighter part, and it solely exists if the light source has a larger diameter than the opaque object.
We can witness the light source’s outer rim around the object casting the shadow in the antumbra. If an observer is standing inside the antumbra during an annular solar eclipse, that person will be able to see the edge of the Sun’s disk as a “ring of fire” around the Moon.
The penumbra is the outer part of a shadow, while the antumbra is the shadow that begins where the umbra ends. If a celestial body, such as the Earth, enters the Moon’s shadow, then we will experience a solar eclipse; however, if the Moon travels through Earth’s shadow, we will witness a lunar eclipse.
Every category of the eclipse depends upon the type of shadow which is cast upon a celestial object. Total eclipses are among the rarest types of eclipse, and apart from them, the umbra may is responsible for a partial eclipse.
When it comes to the penumbra, it is responsible for the partial solar eclipse, partial lunar eclipse, and the penumbral lunar eclipse. In the case of the antumbra, it can only cause annular solar eclipses.
Annular Solar Eclipse
When the umbra’s diameter decreases, it creates a V-shaped shadow core, and if it falls on Earth, it creates an annular solar eclipse. In contrast to the umbra, the antumbra’s diameter increases with a growing distance from the Moon.
When these two shadows meet, the area they create appears similar to an hourglass. Since the antumbra starts beyond the Moon’s umbra at a certain distance, it doesn’t form if the shadow hits a solid object within the umbra’s range.
That is the case during a total solar eclipse when the Moon’s umbra covers the Earth. Unless a total solar eclipse is in process, then the Moon’s dark side experiences an annular solar eclipse.
Annular solar eclipses are rare since the Moon’s antumbra rarely hits the Earth. During an annular solar eclipse, the antumbra covers a very small area on Earth.
Since both the Earth and the Moon are in constant motion, the antumbra moves across the Earth’s surface during an eclipse, and thus it can be seen along a narrow eclipse path.
For example, the annular solar eclipse, which occurred on February 26, 2017, was only visible along a slim belt stretching from southern Latin America to central Africa and parts of the South Pacific Ocean and the South Atlantic Ocean.
Why are Only Some Solar Eclipses Annular?
The Sun’s apparent size matches that of the Moon, where the two spot V-shaped shadows meet, and the umbra turns into the antumbra, marking the location.
From that spot, the Sun and Moon appear equally large. If one would move closer to the umbra, the Moon’s apparent size increases and the Sun is still completely obscured.
If one will move away from the Moon and into its antumbra, its size decreases, and the Sun’s outer edge becomes visible – the ring of fire.
Since the Moon’s orbit around the Earth is highly elliptical, its distance changes constantly. The Moon’s umbra regularly falls on Earth when it is located closest to us, resulting in a solar eclipse.
Conversely, an annular solar eclipse is visible from Earth if the Moon’s distance is greater during the eclipse and the antumbra reaches us.
How Large is the Moon’s Antumbra?
The size of the Moon’s antumbra solely depends on the Moon’s distance from us. If the Moon is farther away, then the antumbra is larger.
The antumbra’s path, on average, reaches a width of just over 60 miles / 100 kilometers at the Earth’s equator. At higher altitudes, the antumbra’s size grows according to the Sun’s rays.
If the distance between the Moon and the Earth is smaller, then only the tip of the V-shaped antumbra will reach our planet during parts of the eclipse. Thus its diameter will be around zero.
Due to the Earth’s curvature, an eclipse may begin as an annular solar eclipse initially. It may later turn into a total solar eclipse, which is a rare phenomenon called a hybrid eclipse.
Why are There No Antumbral Lunar Eclipses?
The Moon doesn’t experience an antumbral lunar eclipse due to the Earth’s size and its distance. The Earth’s umbra is too large for its antumbra to affect the Moon.
However, Earth’s antumbra may reach other planets in our Solar System, such as Mars, due to its greater distance. When the Earth, Sun, and Mars line up, the Earth’s antumbra will be cast upon Mars, and if you were on its surface then, you will see the Earth as a black dot in the sky, in the same field of view as the Sun.
When is the Next Annular Solar Eclipse?
The next annular solar eclipse will occur on June 10, 2021. It will be visible from much of Europe, Asia, North and West Africa, North America, Atlantic, and the Arctic.
Did you know?
- Every planet with natural satellites can experience eclipses. Jupiter, for example, experiences a triple eclipse once or twice every ten years. Three of the four Galilean moons, respectively Io, Callisto, and Ganymede, are responsible for these eclipses. When it comes to Pluto, both it and its giant moon Charon experience eclipses only on one of their sides.
- NASA is always working on predicting lunar eclipses. Their list of predictions extends until the year 2100.
- We won’t experience total eclipses forever. Millions of years in the future, our Moon will be too far away to completely occlude the Sun.
- When our Earth experiences an eclipse, we continue to receive at least 92% of the amount of sunlight.
- A total lunar eclipse can last up to an hour and three quarters. Solar eclipses are much shorter, and they can last up to seven minutes.
- Annular solar eclipses may occur every five or six months.
- An annular solar eclipse may last for a maximum of 12 minutes and 30 seconds.