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Once. That is how many times the Beatles passed through Montreal to perform. 

Another once-in-a-lifetime opportunity will present itself to Montrealers on Monday. As you are no doubt already aware, much of the island will be situated along the path of totality during the solar eclipse. From the vantage point of those who stand along this path, sunlight will be completely blocked by the moon for a short time.   

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The next time that this awe-inspiring celestial show will pass through town will be 180 years from now. So unless you intend to chase the path of totality elsewhere on the globe, you are as likely to experience another total solar eclipse during your lifetime as you are to see John Lennon and the boys.  

Over the past weeks, I have been trying to gauge the Montreal community’s level of eclipse fever. Despite excellent media coverage, I am not sure people quite get it. Chats with students reveal they are unaware of just how different this will be from, say, the partial solar eclipse they recall standing in a field to witness in 2017.  Their parents, having never seen a total solar eclipse either, may also be wondering what the fuss is all about. 

My colleagues in the physics department at Vanier College, on the other hand, have been counting down the days for months. We are like Swifties gearing up for the Eras tour.  

The path of totality is the path along which complete shade from the sun will occur at some point during the day. Imagine a black, 200-km wide curve drawn across the map. Throughout the afternoon of April 8,  a giant spot of total shade will follow this curvy path northeast across the United States at a speed of around 2,400 km/h,  making its way to our neck of the woods just before 3:30 p.m.

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Montreal Island happens to be situated on the northern edge of the path, so much of the island will experience totality, near-total darkness, for just one minute. A 100-km drive southeast would increase this time interval to about 3 ½ minutes. (Laval, Île-Bizard and some parts of Montreal Island, mostly in the east and north ends, are not in the path.)

To illustrate why Montreal will experience a shorter totality than, say, Magog, shine a flashlight in a dark room, and slowly rotate it left to right. You will notice that regions in the top and bottom of the circular spotlight are lit up for less time than those in the middle of the path as the light swings by. A total solar eclipse is like this, but instead of a circular spotlight sweeping across the land, it is a circular shadow.

Totality will take place at about 3:27 p.m. in Montreal (it will hit the West Island only seconds before downtown). The sun will be partially blocked in the time leading up to and following totality. These time periods will look familiar to anyone who has already seen a partial solar eclipse: The moon will gradually cover and then uncover the sun. As such, sunlight will gradually dim and later brighten, and it will be important for spectators to wear eclipse viewing glasses if they wish to stare directly at it. 

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As the sun becomes almost completely blocked, the real show will begin.  

As totality approaches, a line of total shade will race toward you. Now is the time to take off those eclipse glasses. Yes, you read that correctly! If you do not take those glasses off, you will see absolutely nothing — a monumental anticlimax! A rough guide for safe eclipse viewing in Montreal goes as follows: 

• 2:14 – 3:27 p.m.: partial eclipse, wear eclipse glasses to stare at the sun.
• 3:27 – 3:28 p.m.: total eclipse, remove glasses, look up in awe. 
• 3:28 – 4:36 p.m.: partial eclipse, wear eclipse glasses to stare at the sun. 

For the minute or so of totality, it is as safe to look up with the naked eye as it is to stare at stars in the night sky. Only on this occasion, you will see planets and stars in the day sky! You will feel noticeably colder during that brief minute. And you will not be able to take your eyes off the sun’s corona (effectively, its outer atmosphere), which now outlines the moon.

This is the moment that total eclipse chasers call unforgettable; they get emotional even talking about it.

The moon is such a perfectly sized lid for the sun’s light by a celestial coincidence. The sun’s distance from us is 108 times greater than its diameter. The moon’s distance from us is also 108 times greater than its diameter. Put otherwise, the moon is so much closer to us than is the sun, but its diameter is as many times smaller.   

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Try this simple experiment: Look out the window and pick a large somewhat circular object you see in the distance. It’s spring, so a pothole is an excellent choice. Now, with one eye closed, find the precise location to place your thumb such that it just barely removes the pothole from your sight. The pothole is the sun, your thumb is the moon.

There is no astrophysical reason why these distance-to-diameter ratios should be the same, but they are. It is as though nature conspired with the intent to prepare this show for us. What’s more, its visit to our town has coincided with our lifespans. How lucky are we? 

There is an important caveat: If Monday is cloudy in Montreal, we will experience almost none of this. It will still get as dark as night for about a minute, but no afternoon stars or planets, and no solar corona. You know those people in your life who have been bringing up this eclipse in conversations for the past months? If Monday is cloudy, find them; they will need a hug. 

On April 8, make a family day of it, or, if you cannot get off work, take a 15-minute break, and have your breath taken away. We will find ourselves in a privileged place on the planet during our intricate orbital dance with the sun and moon. Let us hope for clear skies and celebrate this magical event together.  

Stephen Cohen teaches physics at Vanier College and is the author of Getting Physics: Nature’s Laws as a Guide to Life.   

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