Annular Solar Eclipse

What is an annular solar eclipse? When does this phenomenon occur? Read to find all the answers...
Life is a game of light and shadows and it continues on a grand cosmic scale in the form of solar and lunar eclipses. As the large shadow of the Moon, positioned exactly between the Earth and Sun, passes rapidly over the spinning Earth, a solar eclipse can be observed in the path of the shadow, as it travels across the Earth's surface. Of the many types of eclipses that may be observed, a rare kind is the annular solar eclipse, which is the topic of discussion in this Buzzle article.

What are Solar Eclipses?

Let us investigate what is this 'shady' business of eclipses, before moving on further to understand the special case of an annular solar eclipse. The Earth revolves around the Sun and Moon revolves around the Earth. A shadow is caused by the obstruction of light by any object as you hold it in front of a light source. Both the Earth and Moon cast gigantic shadows across space and once in a while they get aligned in a line with the Sun on one end, to create the events which we call eclipses. A lunar eclipse is caused when the Moon, Earth and Sun get aligned in a straight line and the Earth casts a shadow over the Moon, 'eclipsing' it in the process.

On the other hand, when the Moon gets aligned in a straight line between the Earth and the Sun (on a New Moon), the moon casts a shadow on the Earth. Any person standing in the path of the dense shadow (called umbra) cast by the Moon, will see the Sun being covered by the lunar disk, giving rise to a total solar eclipse. Those who stand outside the dense part of the shadow (in the penumbra of Moon's shadow), will observe a partial solar eclipse.

This phenomenon of a total solar eclipse is illustrated in Figure 1, on the right hand side of this write-up. You can clearly identify the cone tip of the dense shadow (umbra) touching the Earth's surface, causing a total solar eclipse. An annular eclipse is related to the second possibility illustrated in Figure 2, where the Moon is further away from Earth and the 'Umbra' cone doesn't reach the Earth. Let me explain this phenomenon in more detail.

When Does an Annular Solar Eclipse Occur?

In the case of an annular eclipse, the whole solar disk is not completely covered by the Moon as its umbra cone tip never reaches the Earth. As the tip of the umbra passes over the Earth's surface, the regions which are exactly opposite to it observe the moon covering the central part of the Sun, while leaving a concentric bright ring visible around the central circular dark region. This 'Annular' ring seen during the eclipse is the reason why the phenomenon is known by the name of an annular eclipse. While Figure 2 shows an exaggerated view from Earth, it should give you an idea about what it looks like.

When is the Next One?

The next eclipse annular will be seen on 20th May, 2012 and will be seen through select regions across the world, which includes North America, the Pacific ocean area and Asia. For more details about the exact path of the eclipse shadow across Earth and the timing, visit the NASA Website. Here is a table showing the dates of all future Annular Eclipses, along with specification of regions across which, it'll be seen.

Future Annular Solar Eclipses
DateGeographic Regions of Visibility
May 20, 2012Western USA, Japan, China, Pacific
April 29, 2014Antarctica
September 1, 2016Central Africa, Indian Ocean, Atlantic Ocean, Madagascar
Dec 26, 2019India, Sumatra, Borneo, Saudi Arabia
June 21, 2020China, South Asia, Central Africa, Pacific Ocean

Thus, this special type of eclipse occurs when the tip of the moon's shadow cone (umbra) doesn't reach the Earth, due to which the moon's diameter cannot cover the Sun. The next annular eclipse can be observed on May 20, 2012 and will be seen through Asia, North America and the Pacific ocean. Brace yourself for a treat offered by the heavens as the Earth, Moon and Sun engage in a game of hide and seek!