Q and A with the experts: Unlocking the wonders of a solar eclipse

On April 8, 2024, sky gazers and astronomy enthusiasts in southern Ontario will be treated to a spectacular once-in-a-lifetime event — a total solar eclipse. This rare marvel occurs when the Moon completely covers the Sun, sweeping a shadow over us to reveal a mesmerizing solar corona.  

We recently asked Dr. Roan Haggar, a postdoctoral fellow and the outreach co-ordinator for the Waterloo Centre for Astrophysics (WCA) at the University of Waterloo, to share the science behind the solar eclipse so we can better understand this phenomenon as it passes over us.

What is a solar eclipse, and why does it happen? 

A solar eclipse can only happen during the Moon's first lunar phase. Known as the New Moon, it aligns with the Sun and Earth. While the Sun is 400 times larger than the Moon, it also happens to be situated 400 times farther away from Earth. As a result of this significant distance contrast, the two celestial bodies are seen as the same size when observed from Earth. When the Moon transits between the Earth and the Sun it eclipses our view, causing the Sun's rays to be blocked and casting a shadow onto the face of the Earth.

Why don’t we have a solar eclipse every month? 

The Earth orbits the Sun once per year, and at the same time, the Moon orbits around the Earth. However, the Moon’s orbit is tilted, which means, the Moon is usually either above or below the Earth’s orbit. There are only certain times of the year when the Moon moves level with the Earth and the Sun, making experiencing a total eclipse rare. 

How rare is a total solar eclipse?

The Earth and Moon have predictable orbits, which is how we can predict when and where an eclipse will occur. While a total solar eclipse happens on Earth every one to two years, this is the first time it will happen in Southern Ontario since 1925 and it won’t happen again until 2144. 

Waterloo will see only a partial eclipse on April 8, where approximately 99 per cent of the Sun will be blocked by the Moon. However, a total eclipse will be visible from much of southern Ontario, so you don't need to travel far to see one. To learn more about where you can see a total solar eclipse, visit the WCA website. 

What time of day will the solar eclipse occur in Ontario? 

There are four phases to expect during the solar eclipse:

• First phase: In the afternoon, the Moon will start to pass in front of the Sun and a partial eclipse will begin as it blocks its light.
• Second phase: Approximately an hour later, the Sun will become entirely blocked by the Moon, and a total eclipse will begin. During totality, the Sun, Earth and Moon will become perfectly aligned with one another. This moment of alignment is called "eclipse maximum" and will last only for a few minutes. In southern Ontario it will occur at around 3:20 p.m. 
• Third phase: After the eclipse maximum, the third phase will begin and the Sun will peek out from behind the Moon. 
• Fourth phase: During the final phase, the Moon will fully move past the Sun, the eclipse will end and the Sun will be shining again.

What happens once the Moon covers the Sun? 

The Moon is always moving in relation to the Earth and the Sun, which is why phase two of the eclipse will only last a few minutes. As we experience the eclipse it will get darker over the hour, then become night-time for a few minutes. The temperature will drop, stars will come out and you will be able to see the corona of the Sun.  

What are the dangers of looking directly at a solar eclipse? 

When watching a solar eclipse, you must look through safe solar viewing glasses to avoid damage to your eyes. Safe solar viewers are at least one thousand times darker than ordinary sunglasses. The only safe time to look at an eclipse without glasses is during totality (when the Sun is completely blocked by the Moon). Since we will not experience a total eclipse in Waterloo region, it will not be safe to view it with your naked eye. Even just one per cent of the Sun’s eclipse is enough to damage your eyes.

For more information on eclipse eye safety, check out this Q&A with Dr. Ralph Chou.