Total solar eclipses will disappear

There are few celestial events in human history as dazzling and celebrated as a solar eclipse. About twice a year, the Moon appears to pass in front of the Sun, and if the alignment is imperfect, it causes a partial solar eclipse. However, if the Earth, Moon and Sun align perfectly it will result in a total or annular solar eclipse..

When viewed from Earth, both the Sun and Moon have an angular size (the apparent size of an astronomical object expressed in angles) of about half a degree in the sky, allowing for perfect overlap in perspective. But this is just a coincidence: this fact was not true in the past and will not be true in the future..

According to Kepler’s first law, both the Earth’s orbit around the Sun and the Moon’s orbit around the Earth are ellipses, so sometimes the Moon appears larger than the Sun and casts its shadow down to the Earth’s surface, and sometimes the Sun appears larger so that the lunar disk does not completely cover the solar disk.

But about 4.5 billion years ago, according to the main theoretical models of the formation of the Solar System, a collision between the planet Earth and a Mars-sized object caused the debris from that collision to coalesce into the Moon. The Moon was much closer to our planet, and it was spinning much faster.

During this period, a day on Earth was much shorter, lasting six to eight hours instead of the 24 hours we know today. But thanks to the tidal forces exerted by the Moon on the spinning Earth, our day gradually became longer over the billions of years that passed. This is still happening today: With each passing year, it takes about 14 more microseconds for the Earth to complete its daily rotation..

Therefore, to compensate for the lag in the calendar, it is necessary to add a “leap second” every 18 months. This is a very slow but continuous and cumulative process. Thanks to our orbital interaction with the Moon, in about 4 million years, an Earth year will be exactly 365 days long, which will eliminate the need to add February 29 to our calendars for leap years.

But the increasing length of a day on Earth comes at a cost. According to the laws of nature conservation, every effect is caused by an equivalent cause: As the Earth’s rotation slows down, the Moon is pushed backwards and moves further and further away from the Earth..

Consequently, the farther away the Moon is, the smaller its angular size and therefore the smaller it appears in the sky.

Currently, the Moon’s rate of retreat due to conservation of angular momentum is about 3.8 centimeters per year, something imperceptible today but will be significant millions of years from now.

Therefore, fewer total solar eclipses will become possible as time goes on, and almost all such events will be annular. The angular size of the lunar disk is not enough to block the Sun..

Today, solar eclipses are divided almost 50% into total and annular, but the last total solar eclipse will occur in about 650 million years, because after that point the Moon will no longer be close enough to the Earth at any point in its orbit for its shadow to fall on our surface.

If humanity survives until then, The only way to see a total solar eclipse would be to take to the skies and fly into space, where we would once again be under the shadow of the moon..

The finiteness of total solar eclipses is an example of how even the greatest things in the cosmic vastness pass away in due time.