How Solar Eclipses Work

By: Craig Freudenrich, Ph.D.  | 
A picture of the moon covering the sun during a solar eclipse.
The moon blocks out the sun's surface in a total solar eclipse. Matt Anderson Photography / Getty Images

A solar eclipse is a celestial phenomenon that does not occur very often, but they are fascinating to watch when they do. On those rare occasions when you are in the right place at the right time for a full solar eclipse, it is amazing.

In this article, we will see what happens during a solar eclipse and how you can observe this incredible event safely.


What Is a Solar Eclipse?

Positions of the sun, moon and Earth during a solar eclipse. Umbra and penumbra are regions of the moon's shadow.
Photo courtesy NASA

A solar eclipse occurs when the moon passes in a direct line between the Earth and the sun. The moon's shadow travels over the Earth's surface and blocks out the sun's light as seen from Earth.

Because the moon orbits the Earth at an angle, approximately 5 degrees relative to the Earth-sun plane, the moon crosses the Earth's orbital plane only twice a year. These times are called eclipse seasons, because they are the only times when eclipses can occur. For an eclipse to take place, the moon must be in the correct moon phase during an eclipse season; for a solar eclipse, it must be a new moon. This condition makes solar eclipses relatively rare.


Types of Solar Eclipses

Total solar eclipse
Photo courtesy NASA

The moon's shadow has two parts: a central region (umbra) and an outer region (penumbra). Depending upon which part of the shadow passes over you, you will see one of three types of solar eclipses:

  • Total Solar Eclipse - The entire central portion of the sun is blocked out.
  • Partial Solar Eclipse - Only part of the sun's surface is blocked out.
  • Annular Solar Eclipse - Only a small, ring-like sliver of light is seen from the sun's disc.


Total Solar Eclipse

A total solar eclipse is a breathtaking celestial event that takes place when the Moon crosses directly between the Earth and the Sun, obscuring the Sun's entire disk. As the Moon aligns perfectly, it momentarily appears to completely block out the Sun's bright face, allowing the solar corona—the Sun's outer atmosphere—to become visible as a shimmering halo of light. Daylight dims significantly, and the surrounding environment takes on an eerie twilight glow.

Observers lucky enough to be within the eclipse's path of totality experience the awe-inspiring sight of the Sun's brilliant disk being transformed into a stunning celestial ring, or "diamond ring" effect, just before and after the total phase. To safely witness this captivating phenomenon, specially designed eclipse glasses are essential to protect the eyes from the Sun's intense rays. However, a total solar eclipse is the only type where you can momentarily remove your eclipse glasses for a brief period when the moon is completely blocking the sun.


Partial Solar Eclipse

A partial solar eclipse occurs when only a portion of the Sun is obscured by the passing Moon. Unlike the complete coverage of a total solar eclipse, during a partial eclipse, the Sun's disk remains partially visible, creating a remarkable crescent-like shape.

While the overall daylight may not significantly diminish, the environment takes on a subdued quality as the Moon's silhouette delicately encroaches upon the Sun's brilliance. It's important to emphasize that even during a partial solar eclipse, observing the event directly with the naked eye can cause damage, making the use of proper eye protection, such as eclipse glasses, essential.


Annular Solar Eclipse

An annular solar eclipse is a remarkable celestial phenomenon that occurs when the Moon passes between the Earth and the Sun, but the Moon's apparent size is slightly smaller than the Sun's, resulting in the Sun appearing as a bright ring, or "ring of fire," around the edges of the Moon's silhouette.

This unique event happens when the Moon is at a point in its orbit that is farther away from the Earth, causing it to appear smaller in the sky. As the Moon partially covers the Sun, the surrounding landscape takes on an otherworldly quality, and observers witness the striking visual spectacle of the Sun's radiant rim framing the Moon's dark center.


Hybrid Eclipse

It's also important to know what a hybrid eclipse is. A hybrid solar eclipse, also known as an "annular-total eclipse," is a rare and fascinating event that occurs once every decade. A hybrid eclipse transitions between an annular eclipse and a total eclipse along its path. Depending on an observer's location, a hybrid eclipse may appear as a total eclipse in some areas and an annular eclipse in others.

This intriguing phenomenon occurs when the curvature of the Earth's surface influences the alignment between the Sun, Moon, and observer, leading to an eclipse that shifts from one type to another, creating an unforgettable visual experience for those fortunate enough to witness it.


How to Watch a Solar Eclipse

Never look at the sun directly -- doing so can damage your eyes. The best way to observe the sun is by projecting the image. Here is one way to project the sun's image:

  1. Get two pieces of cardboard (flaps from a box, backs of paper tablets).
  2. With a pin or pencil point, poke a small hole in the center of one piece (no bigger than the pin or pencil point).
  3. Take both pieces in your hand.
  4. Stand with your back to the sun.
  5. In one hand, hold the piece with the pinhole; place the other piece (the screen) behind it.
  6. The sunlight will pass through the pinhole and form an image on the screen (see How does a pinhole camera work? for details on this process).
  7. Adjust the distance between the two pieces to focus and change the size of the image.

Enjoy observing!


For more information on solar eclipses and related topics, check out the links that follow.


More Great Links


Solar Eclipse FAQ

How often do solar eclipses occur?
Solar eclipses happen once every year-and-a-half or so; the trick is you're not always able to see them based on your vantage point on Earth.
How does a solar eclipse work?
A solar eclipse occurs when the moon passes in a direct line between Earth and the sun, and the three bodies are lined up.
What are the types of solar eclipses?
The three main types of solar eclipses are partial solar eclipses, total solar eclipses, and annular eclipses. In a partial solar eclipse, only a portion of the Sun is obscured by the Moon. In a total solar eclipse, the Moon completely covers the Sun, revealing the Sun's corona. An annular eclipse occurs when the Moon is farther from the Earth, resulting in a ring-like appearance of the Sun around the Moon's silhouette.
Does a solar eclipse affect humans?
A solar eclipse does not have a direct physiological effect on humans. However, it can evoke awe and wonder, impacting human emotions and cultural perceptions. Looking directly at the eclipse, on the other hand, can be dangerous..
Why is a solar eclipse is dangerous?
A solar eclipse can be dangerous since it can damage your eyes if you look directly at the sun. The best way to observe the sun is by projecting the image.
What was the eclipse called in 2017?
The 2017 eclipse was called the Great American Eclipse.