On April 8, many students left class, put on viewing glasses and watched as the world went dark during the day. They experienced a phenomenon known as a solar eclipse, and while it was beautiful, many people still don’t understand the science behind what they  experienced.

Eclipses happen when the Earth, Moon and Sun are lined up in their orbital paths. Exactly how they align determines the type of eclipse we see. A solar eclipse happens when the moon passes between the Sun and the Earth, casting a shadow on the sun, and making it appear covered, like we all experienced last month.

Solar eclipses only occur during a new moon, when we see no light reflecting off the moon, and when the moon and the sun are on the same side of the Earth. New moons happen once every month, but solar eclipses are a much rarer occurrence. This is because the moon travels on a different orbital plane than the Sun and Earth, about five degrees upward. Typically, during a new moon, the moon passes below or above the Sun. In fact, there are only two times a year, called eclipse seasons, when the moon passes the Earth-Sun (ecliptic) plane and solar eclipses are made possible.

A total solar eclipse happens when the moon completely blocks off all light from the Sun, which is what we experienced last month. Even though the Sun is 400 times bigger than the moon, it’s also 400 times farther away than the moon, making the Sun and the Moon appear the same size in Earth’s sky 

During a total solar eclipse, the Moon moves in front of the Sun and covers the solar disc. The shadow that the moon casts has two parts: the umbra,the darker, inner shadow, and the penumbra, the fainter outer shadow. To see a total solar eclipse, eclipse viewers must be within the reach of the umbra

While the last two total solar eclipses that were visible in Wisconsin were only seven years apart, the next total solar eclipse visible in the state won’t be until 2099. However, the next total solar eclipse in the U.S. will be in 2044, passing through the country’s southern states. Though many people may only see them as a quirk of nature, total solar eclipses are a symphony of many cosmic phenomena lining up, such as the new moon, the moon passing the Sun-Earth orbital plane and the path of the umbra. With how rare and spectacular it is, a total solar eclipse is definitely a spectacle that is worth the 20-year wait.