An eclipse occurs when some or all of the light from one celestial object is blocked by another celestial object passing between it and an observer. In the case of a solar eclipse, the Moon passes between the Sun and Earth, blocking the light from the Sun as seen by an observer on Earth.

Credit: NASA’s Goddard Space Flight Center

One amazing coincidence of our solar system is that the Moon and Sun, as seen from Earth, are approximately the same angular size. This means that they take up the same amount of space in Earth’s sky, allowing the Moon to perfectly block out light from the Sun when the two are aligned.

Though we are close to the path of totality in Williams Bay, we will experience only a partial eclipse. About 90% of the Sun’s light will be blocked by the Moon at peak eclipse (around 2pm CT).

Maximum eclipse during the April 8, 2024 solar eclipse in Wisconsin will occur just after 2pm CT, with about 90% of the Sun’s light blocked by the Moon.

First things first – it is not safe to look directly at the Sun without special equipment. You may have heard there is a caveat to this during a solar eclipse – while it’s true that you can look directly at a total solar eclipse during the few minutes that the Moon is completely blocking the light from the Sun (totality), you generally should not look at the Sun with just your eyes during a solar eclipse.

For the April 8, 2024 total eclipse
With the exception of the few minutes of totality, you should always use protective measures while observing this eclipse.

Here are some options for safely observing the Sun during an eclipse:

Eclipse glasses
These special glasses use solar filters that block out more than 99% of the Sun’s light, making it safe to look directly at the Sun while wearing them. It is crucial that you buy these from a trustworthy source, as using counterfeit or damaged glasses could cause permanent eye damage. The American Astronomical Society has compiled an extensive list of approved suppliers of eclipse glasses for your reference.

Pinhole observers
Projecting the Sun’s light using a pinhole observer is another safe and easy way to view a solar eclipse. Check out these instructions for how to build your own pinhole observer with common household items.

Specialty filters and telescopes
Though this option is a bit more expensive, you can purchase your own specialty filters to safely view the Sun with a telescope or binoculars. All of the filters block out at least 99% of the Sun’s light, making it safe to look directly at the Sun using your instruments. Some filters only let a certain wavelength, or color, of light through, allowing a unique view of different components of the Sun. The American Astronomical Society has also compiled an extensive list of recommended filters and telescopes for your reference.

A partial solar eclipse occurs when only some of the Sun’s light is blocked by the Moon. This happens when the Sun and Moon are not perfectly aligned when viewed from Earth.

An annular solar eclipse occurs when the Moon and Sun are aligned as seen from Earth, but the Moon is at the farthest point from Earth in its orbit. Because the Moon appears smaller when at its farthest point from Earth, the Sun is not completely covered during an annular eclipse. This creates the characteristic ring around the Sun that is observable during an annular eclipse.

A total solar eclipse occurs when the Moon and Sun are aligned as seen from Earth, with the Moon completely blocking the light coming from the Sun’s surface. Because Earth’s surface is curved, some solar eclipses can shift between annular and total depending on the observer’s location. An eclipse that shifts between annular and total is known as a hybrid solar eclipse.

It’s a common misconception that solar eclipses are rare. Partial solar eclipses happen at least two times a year, and the most sought-after eclipse – a total solar eclipse – happens approximately once every 18 months. Although solar eclipses happen quite frequently, the location an eclipse is visible changes from eclipse to eclipse. This is what gives solar eclipses a sense of rarity; observers often have to travel great distances to be able to experience an eclipse.