How will the total solar eclipse on April 8 take place?

Total solar eclipses are so rare that a given location on Earth is only likely to be seen once every 375 years on average. And when a solar eclipse occurs, it is completely visible only to those traveling along a narrow path on Earth. The upcoming total solar eclipse on April 8 will open a new approach.

Determine the date

The combination of the time and rare location of a total solar eclipse helped researchers narrow down the exact date when the recorded eclipse was seen by ancient people. Additional clues such as the time of day (morning, noon, or evening) the eclipse occurs, the time of year (season), or the presence of bright planets can also help pinpoint the eclipse.

Photo of the 2017 total solar eclipse, taken at the Oregon State Fairgrounds, Salem, USA. (Photo: Dominic Hart/NASA).

One of the oldest solar eclipses recorded was on a clay tablet in the city of Ugarit, in modern-day Syria. The city collapsed shortly after the eclipse, making the tablet one of the last things written by anyone there. The inscription on the stele reads: "… the day of the new moon in ḫiyaru, the Sun sets, its gatekeeper is [Rashap]".

The word ḫiyaru refers to the time of year around February/March and Rashap may be a planet. Researchers dated the tablet and eclipse to March 5, 1222 BC, more than 3,000 years ago, when Mars was visible near the eclipsed sun. Thanks to this eclipse, we know that Ugarit fell shortly after March 5, 1222 BC.

Records like these help researchers determine precise dates in the ancient world.

A day on Earth is getting longer by one second every 55,000 years

Accurately predicting future eclipses or the paths of historical eclipses requires knowing the positions of the sun, moon, and Earth. The computer can track each movement, but the challenge is that these movements are not fixed. As the moon causes tides in Earth's oceans, this process also causes the moon to gradually drift away from the Earth and the length of the day on Earth gradually increases.

Essentially, the length of a day on Earth is getting longer by about 18 microseconds every year, or one second every 55,000 years . After hundreds or thousands of years, those fractions of seconds each day will add up to several hours.

By timing solar eclipses over the past 2,000 years, researchers have mapped out the length of days on Earth over that same period. A value of 18 microseconds per year is the average, but sometimes the Earth slows down a little and sometimes a little less.

We can now measure the change in the length of a day on Earth with instruments, but we wouldn't have been able to record that change hundreds or thousands of years ago without an accurate measure. and records of eclipses over millennia and around the world. Total solar eclipses allow us to look into Earth's history.