An annular solar eclipse is a celestial spectacle that captivates skywatchers and astronomy enthusiasts around the world. It occurs when the New Moon’s apparent diameter is smaller than the Sun’s, blocking most of the Sun’s light and causing the Sun to look like a ring (an annulus). This phenomenon is the reason behind the term “ring of fire” eclipse. Here is a look at the nature of annular solar eclipses, their differences from total solar eclipses, and guidance on safe viewing and photography.
What Is an Annular Solar Eclipse?
An annular solar eclipse happens when the Moon passes between the Earth and the Sun, but the apparent size of the Moon is smaller than that of the Sun. This creates the appearance of a bright ring or annulus surrounding the dark disk of the Moon. The “ring of fire” is visible from within a narrow pathway on the Earth’s surface, known as the path of annularity. Outside of the path of annularity, there is a band where a partial solar eclipse occurs.
Why Is it Called a “Ring of Fire” Eclipse?
The term “ring of fire” refers to the bright, ring-like appearance of the Sun as seen from Earth during an annular solar eclipse. As the Moon does not completely cover the Sun, a brilliant ring of sunlight is visible encircling the Moon’s silhouette.
What to Expect
An annular eclipse includes a partial solar eclipse, but it differs from a total solar eclipse. Here is what you can expect:
- The sky dims, but it never gets completely dark. Even so, it’s brighter all around the horizon.
- At maximum eclipse, the Sun looks like a ring of fire around a black Moon. You still need eclipse glasses when this happens.
- At maximum eclipse watch for Baily’s beads. These are especially bright spots around the Moon caused by lunar valleys letting more sunlight pass.
- Watch for shadow bands on the ground.
- Solar flares and prominences may be visible for some annular eclipses. Usually, the ring of fire drowns them out.
- The “diamond ring” effect occurs just before and after the point of maximum eclipse, but it is not as well-defined as for a total eclipse.
You won’t see the diamond ring effect, solar flares, or solar prominences wearing eclipse glasses. However, some telescopes and camera with different filters pick up these phenomena.
Conditions Necessary for an Annular Eclipse
An annular solar eclipse requires a specific set of conditions:
- New Moon: The phase of the Moon must be new, meaning the Moon is situated between the Earth and the Sun.
- Alignment: The Earth, Moon, and Sun must be aligned in such a way that the Moon’s shadow falls upon Earth’s surface.
- Distance: The Moon must be near its apogee, the point in its elliptical orbit where it is farthest from the Earth. At this distance, the Moon appears smaller in the sky and is unable to cover the Sun completely.
Difference from a Total Solar Eclipse
The fundamental difference between an annular and a total solar eclipse lies in the apparent size of the Moon relative to the Sun:
- Annular Eclipse: The Moon appears smaller than the Sun, leaving a visible ring of sunlight.
- Total Eclipse: The Moon completely covers the Sun, casting a shadow that turns day into night for a short period. This occurs when the Sun and Moon appear the same size or when the Moon appears larger than the Sun (near perigee).
Partial Eclipse with an Annular Eclipse
Before and after the peak of an annular solar eclipse, observers outside the path of annularity but within a certain geographic range experience a partial solar eclipse. In this phase, the Moon covers only a part of the Sun, casting a crescent-shaped shadow on Earth.
Also, there is a band outside the path of annularity that sees a partial solar eclipse because the Sun and Moon don’t perfect align.
Viewing an Annular Eclipse Safely
Observing an annular eclipse requires precaution to prevent eye damage. Here are safe viewing methods:
- Projection Method: Project the image of the Sun onto a white surface with a pinhole projector or a telescope. The light passing through a colander or the leaves of trees also shows the eclipsed Sun.
- Solar Viewing Glasses: Use solar viewing or eclipse glasses that meet the ISO 12312-2 international safety standard.
- Solar Filters: Attach a solar filter to the front of a telescope or binoculars.
Viewing an annular eclipse requires eclipse glasses the entire time. While you can view the Sun directly at totality during a total solar eclipse, there is too much sunlight during maximum eclipse during an annular eclipse.
Photographing an Annular Eclipse
Photographing an annular eclipse is an exciting endeavor. Follow these steps to ensure safety and success:
- Use Proper Filters: Equip your camera lens with a solar filter to protect the sensor (and your eyes).
- Choose the Right Equipment: Use a telephoto lens or a telescope with a camera adapter to get a close-up view of the eclipse.
- Use a Tripod: Watching an eclipse is exciting, so expect shaky hands. Use a tripod or at least a camera with image stabilization.
- Plan Your Shot: Research the eclipse timings and choose a good location.
- Practice: Test your equipment and settings before the eclipse.
- Be Prepared: Have backup batteries and memory cards on hand.
The cameras on modern phones are really good, so don’t worry if you don’t have a telescope or camera with a telephoto lens. Use your cell phone, but be sure it’s attached to a tripod because you’ll need to zoom in a bit to get a great shot. Put eclipse glasses over the lens of camera to protect it from the Sun.
Annular Solar Eclipse List
Annular solar eclipses are uncommon. Here are the dates of the annular eclipses up to the year 2030 and where to see them:
- 2023 October 14 (North, Central, and South America)
- 2024 October 2 (Easter Island, Argentina, Chile, Pacific Ocean)
- 2026 February 17 (Antarctica)
- 2027 February 6 (Pacific Ocean, Argentina, Chile, Atlantic Ocean)
- 2028 January 26 (Pacific, South America, Atlantic)
As the Moon moves further away from the Earth, there will be more annular eclipses and fewer total eclipses.
- Harrington, Philip S. (1997). Eclipse! The What, Where, When, Why and How Guide to Watching Solar and Lunar Eclipses. New York: John Wiley and Sons. ISBN 0-471-12795-7.
- Stephenson, F. Richard (1997). Historical Eclipses and Earth’s Rotation. Cambridge University Press. ISBN 0-521-46194-4. doi:10.1017/CBO9780511525186
- van Gent, R.H. (2018). A Catalogue of Eclipse Cycles. Utrecht University.