Silhouette of people watching a total solar eclipse

Total solar eclipse today: Here’s everything you should know

Editor’s note: Looking at a solar eclipse without proper protection can cause eye damage. In most cases, the effects are temporary, but the damage can be permanent. It takes just seconds for damage to occur. Symptoms of eye damage from a solar eclipse include blurry vision, headache, a blind spot in the central vision, sensitivity to light, distorted vision and changes in perception of color. If you experience these symptoms after the solar eclipse, you should contact your ophthalmologist. Learn more about the impact of the solar eclipse on vision.

Today, millions of people across the United States, Canada and Mexico are eager to witness a rare event: a total solar eclipse. This extraordinary occurrence takes place when the Earth, sun, and moon align, a scenario that causes a breathtaking display of darkness. Locations in the “path of totality”—such as Case Western Reserve University’s campus—will experience a momentary twilight that is expected to last for four minutes.

Totality serves as a powerful reminder of our position in the vastness of the universe—one that has captivated civilizations for millennia, with the earliest records dating back to 2500 BCE. 

To learn more about the celestial phenomenon of solar eclipses, The Daily tapped into the expertise of Corbin Covault, professor and chair of the Department of Physics.

Read on to discover Covault’s insights. 

Q: What exactly is a solar eclipse and how does it occur? 

Covault: The Earth orbits the sun (once per year) and the moon orbits the Earth (once every 28 days approximately). The orbital plane of the moon is misaligned with the orbital plane of the Earth by about five degrees, but these two planes cross each other at two points in the sky. When the moon and the sun are simultaneously at one of these two points such that the moon is blocking (or partially blocking) the light from the sun, we have a solar eclipse. More simply: the moon casts a shadow from the sun and whenever the Earth is in that shadow, there will be a solar eclipse.

Q: Could you explain the different types of solar eclipses and what distinguishes them?

Covault: There are three different types of solar eclipses: A partial solar eclipse being the first, where the moon comes in front of the sun to block the light from a part of the surface of the sun but not all of it. In other words, the alignment between the moon and the sun and the observer on Earth is not quite perfect.

The second is an annular solar eclipse, which is an eclipse that happens when the moon and sun are well co-aligned but the moon is further out in its orbit and therefore the disk of the moon is slightly smaller—enough so that it does not quite cover the disk of the sun. This appears as a “ring of fire” in the sky. One of these was visible in the southwest U.S. Oc. 23, 2023. 

The third, which we will witness today, is a total solar eclipse, which happens when the alignment of the sun and moon is very good and the moon is close enough in its orbit to the Earth that the disk of the moon completely obscures the disk of the sun as seen in the sky. Total solar eclipses are the most spectacular because of the dramatic darkening of the sky.

Q: Why are solar eclipses such rare events in certain locations?

Covault: Solar eclipses are “rare” in a very general way. The shadow of the moon on the Earth corresponds to a spot about 200 miles across that moves across the surface of the Earth at high speed (for example, when the totality shadow hits Cleveland it will be moving at about 4,000 miles per hour.)  This means that we will be in that shadow for just under four minutes of totality when the moon fully covers the “photosphere” disk of the sun.

Because the shadow of totality is so small compared to the surface of the Earth, total eclipse events at any location are quite rare, happening once every few hundred years or so. On the other hand, the actual alignment that results in an eclipse somewhere on Earth is not so rare: about once every year or two somewhere at someplace on Earth experiences a total solar eclipse. It’s just rare that this happens close to any given location.

Q: How do solar eclipses impact scientific research and study in the field of astronomy?

Covault: There is a long history of scientists using the unique situation provided by eclipses to make important scientific observations. One of the most famous of these was the 1919 solar eclipse that provided astronomical observation that demonstrated that starlight was being deflected by the gravity of the sun in precise accord with Albert Einstein’s predictions from his theory of General Relativity. [Today],, NASA scientists and others will be launching rockets and taking data.   

Q: What safety precautions should individuals take when viewing a solar eclipse?

Covault: Do not look at the eclipse event without ISO certified protective goggles! Exception: once totality starts and the photosphere of the sun is completely covered by the disk of the moon (a dramatic event!) then you can look at the eclipse without eye protection. Once the sun begins to reemerge from behind the moon immediately stop looking and put the glasses back on.

Q: How do solar eclipses contribute to our understanding of the sun and its behavior?

Covault: The nice thing about eclipses is that you can see parts of the sun that are otherwise very difficult to observe. The main surface of the sun (where most of sunlight comes from) is called the photosphere. The light from the photosphere is literally blinding but is covered during a total eclipse. 

If we are lucky, we may be able to observe parts of the “chromosphere” of the sun. This is a thin region of atmosphere just above the photosphere where interesting features such as solar prominences may be visible, possibly even with the naked eye. Since the sun is in a relatively high period of solar activity, there is perhaps a better-than-usual chance of observing these sorts of things this April. Sometimes the prominences can be spectacular. 

Finally, during a solar eclipse, we can observe the solar “corona” which is a very thin outer atmosphere of ionized gas that can be seen to glow faintly gray or white around the moon during the eclipse. Scientific observation of these things during an eclipse can definitely lead to better understanding of the sun.