Santanu Das


Astro-QA #6 : When will the last total solar eclipse occur?

Our moon is slowly going away from Earth. So once a time will come when the angular diameter of the moon will no longer be enough to cover the Sun completely and the total solar eclipse will never happen again. When will the last total solar eclipse occur?


A total solar eclipse is possible because the angular diameter of the moon in the sky is larger than the angular diameter of the sun. So, given the right conditions, all direct sunlight is blocked at certain points on Earth, from where we see the total solar eclipse.

Every year, the moon moves about 3.8 centimeters farther away from Earth. It is measured by bouncing laser beams off reflectors that several Apollo crews left on the lunar surface. So, one-day the apparent diameter of Moon will become too small in the sky to block the whole Sun.

When the Moon is at its closest and biggest and it can no longer cover the Sun at its farthest and smallest and total solar eclipses will become a history. Fortunately, it’s a long, long way off. When Earth is farthest from the Sun, our star appears 31.5 arcminutes in diameter. When the Moon is closest to Earth, its angular size is 33.5'. For this to shrink to 31.5 ', the Moon’s perigee distance must increase by about 23,000 kilometers. At a rate of 3.8 cm per year, this will take more than 600 million years.

But this situation is complicated by perturbations in the orbits of Earth and the Moon. Belgian astronomer Jean Meeus concludes that, about 620 million years from now, the total solar eclipses will become an on-again, off-again phenomenon, and that the very last total solar eclipse will occur about 1.2 billion years from now.


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