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Annular Solar Eclipse

Annular Solar Eclipse

An annular solar eclipse occurs when the Moon passes directly between the Earth and Sun, but does not completely cover the Sun's disk. Instead, it covers most of the Sun, leaving its outer edge visible as a bright ring or “annulus” around the darkened Moon. This is also sometimes referred to as the “Ring of Fire” effect.

The next annular solar eclipse will occur on October 14, 2023!

Learn More Below!

Why Aren’t All Solar Eclipses Total Eclipses?

The Moon's orbit around the Earth is not a perfect circle; it's slightly elliptical. This means that the Moon's distance from Earth varies throughout its orbit.

When the Moon is near its apogee (the farthest point from Earth in its orbit), it appears smaller in the sky. Conversely, when it's closer to its perigee (the closest point to Earth), it appears larger.

During an annular solar eclipse, the Moon moves in front of the Sun at or near apogee. At this distance, it is not large enough from our perspective on Earth to completely cover the Sun.  
However, during a total solar eclipse, the Moon happens to be in just the right position and just at the right distance from Earth that it exactly covers the relative size of the Sun.

Why Study Solar Eclipses?

At NOAA, we are very interested in solar eclipses because they can help us study certain solar phenomena. While annular eclipses don’t block all the Sun’s light, total solar eclipses do. 

When a total solar eclipse occurs, the Moon completely covers the Sun, providing us with the opportunity to see the Sun’s atmosphere, including the wide, outermost layer known as the corona. This is very dim compared to the brightness of the Sun, and is normally almost impossible to see. However, when the Moon is completely blocking the Sun’s light, the corona shines around it like a halo. 

By studying the corona, we can learn more about the Sun itself, its relationship with the Earth, and in turn, how it can affect us. 

For example, there is still a lot we don’t know about the corona, such as why it’s so much hotter than the sun’s surface (more than 1.8 million degrees Fahrenheit compared to roughly 10,000 degrees Fahrenheit, respectively). During recent eclipses such as the one in 2017, researchers found that even when the sun is covered by sunspots and other surface phenomena, the corona’s temperature stays constant, and they still don’t know why.

Additionally, by studying the sun’s corona, we can learn more about space weather, which can affect us on Earth by disrupting our power grids and communications systems, as well as impacting satellite operations, GPS navigation capabilities, astronauts in space, and more. 

Many of these disturbances are triggered by parts of the solar corona that erupt and detach as huge blobs of plasma that then travel through the interplanetary medium, and pass near Earth, engulfing the planet. These are called coronal mass ejections. Other space weather effects are produced by fast-moving subatomic particles that are launched from the solar atmosphere.

In order to study the corona any time we want, NOAA uses a special instrument called a coronagraph, which mimics the effect of an eclipse by blocking the light from the Sun's disk, but not from its atmosphere. That way, we don't have to wait for a natural eclipse to occur!

NOAA’s newest geostationary satellite, GOES-U, will carry a brand new coronagraph built by the Naval Research Laboratory onboard, officially known as the Compact Coronagraph-1 (CCOR-1). This instrument will provide critical space weather measurements for NOAA’s Space Weather Prediction Center (SPWC).

Future missions that will study space weather include the Space Weather Follow-On Lagrange 1 (SWFO-L1) satellite. This satellite is currently in development, and once launched, will be stationed in deep space at Lagrange Point L1, roughly one million miles away from Earth, between our planet and the sun. This location allows for continuous unobstructed observation of the corona without interference from Earth.