When is the eclipse? Everyone is talking about Monday, April 8, when a total solar eclipse will see the moon’s central shadow create a 115-mile wide path of totality across parts of Mexico, the U.S. and Canada.
Here’s a secret: the eclipse actually begins on April 9. How can that be?
International Date Line
This phenomenon is not unusual, but the “Great North American Eclipse” has a unique geographical quirk. A “tomorrow eclipse” usually occurs when an eclipse begins at a location on the opposite side of the International Date Line. It’s an imaginary line that marks the change of one calendar day to the next. It runs from the North to the South Pole at about 180° east or west—halfway around the world from 0 degrees longitude in Greenwich, London.
Locations just west of the line are 24 hours ahead of locations just east of the line. However, the International Date Line does take a few tangents to make life easier for nations of islands, the most extreme case being the Line Islands of Kiribati. This island nation on the equator consisting of 32 atolls, reef islands and a coral island has the International Date Line swing around it almost to 150 degrees west.
So even though this path of totality begins east of 180 degrees, the eclipse will still appear to start “tomorrow.”
Tale Of Two Timezones
The path of totality will be about 10,000 miles (16,000 kilometers) long and about 115 miles wide as it races across Earth’s surface, but less than half of it moves across land. Like most solar eclipses, it occurs mainly over the sea.
The moon’s central shadow will first touch Earth at sunrise in the Pacific Ocean south of Starbuck Island in Kiribati, where the local time will be 06:41 a.m. LINT (Line Islands Time) on April 9, according to Timeanddate. A 96.8% partial eclipse will occur over here. Oddly, at Penrhyn Atoll—part of the Cook Islands—to the south of the southern limit of the path, it will be 06:39 a.m. CKT (Cook Islands Time) on April 8, and the sun will be eclipsed by 98.5% at the event’s maximum.
The moon’s central shadow will travel through the LINT timezone (“tomorrow time”) and head across around 4,000 miles (6,500 kilometers) of ocean to North America. The moon’s central shadow will take 3 hours, 16 minutes and 45 seconds to cross Earth between 12:39 p.m. EDT and 3:55 p.m. EDT before it departs at sunset in the Atlantic Ocean north of the Azores.
‘Tomorrow Island’ And ‘Yesterday Island’
Sometimes, the position of the International Date Line can cause an even more dramatic geographical oddity during an eclipse—as will during the next total solar eclipse in North America after 2024.
On Wednesday, March 30, 2033, a total solar eclipse will come to western and northern Alaska. But it also occurs in eastern Russia. The Diomede Islands in the Bering Strait will be in the path, which is divided not only between nations but also by the International Date Line. Both will experience totality for 2 minutes 9 seconds with the eclipse 6 degrees above the eastern horizon, according to Timeanddate. But while Big Diomede (Bol’shoy Diomid) in Russia will see it at 05:48 a.m. ANAT on March 31, for Little Diomede just east in the U.S., it will be 09:48 a.m. AKST on March 30.
None of this is unexpected or unusual since the path of totality at every total solar eclipse is typically 10,000 miles (16,000 kilometers) long, so they always cross multiple time zones. In fact, it was also the case for the last total solar eclipse in the southern hemisphere on April 19/20. 2023.
If you’re unsure if your location will see a total or a partial solar eclipse—and at what time—check this interactive map, this eclipse simulator and this eclipse location look-up.
For the latest on all aspects of April 8’s total solar eclipse in North America, check my main feed for new articles each day.
Wishing you clear skies and wide eyes.