Solar eclipses occur due to the moon and sun being the same apparent size, but the moon is gradually receding. When did eclipses as we see them first appear, when will they end and when is/was the “perfect” age for a solar eclipse?
1 Answer
Total solar eclipses have always been visible from Earth since the Moon was formed, the perfect age was about 8 million years ago and the last will be in about 560 million years.
Explanation:
Solar eclipses occur because the angular diameter of the Moon can be greater than the angular diameter of the Sun. This means that when the Sun, Moon and Earth are in alignment, the Moon’s disc can completely cover the Sun’s disc.
The Moon is moving away from the Earth at a rate of about 3.8cm per year. Currently, in a given year there are between two and five solar eclipses. If there is a total eclipse in a given year then there is always a second central solar eclipse. This second eclipse is usually annular because the Moon’s disc isn’t large enough to cover the Sun’s disc.
There was a period when the Moon was closer to the Earth and both central eclipses were total. Total eclipses are more spectacular if the lunar disc is slightly larger than the solar disc as more features of the Sun are visible. There was an optimal time when both central eclipses were total but only just so. This was about 8 million years ago.
As the Moon moves further away from the Earth, total eclipses become increasingly rare. Eventually the Moon’s angular diameter will always be smaller than the Sun’s angular diameter. After this
total solar eclipses will no longer occur. This will be in about 560 million years time.
The calculations for the last total solar eclipse are in this answer https://socratic.org/questions/when-will-the-last-total-solar-eclipse-occur.
