Eclipse Sun

A solar eclipse is the astronomical phenomenon that occurs when the Moon hides the Sun as seen from Earth. This occurs when the Sun, Moon, and Earth are aligned.

On the cover you can see the total solar eclipse seen from Ellis Beach in far north Queensland, Nov. 14, 2012.

Another wonderful image of the solar eclipse on November 13, 2012, in Australia, was published on the Observatory website.

We currently know that the Earth revolves around the Sun and that the Moon is dancing around the Earth. The Moon is a satellite of the Earth.

Solar eclipse
Solar eclipse in Australia year 2012. Credit: Alex Chernay. Web “observatorio.info/2012/11/como-un-diamante-en-el-cielo/”.

Considering these circumstances, it is not strange that, from time to time, the Moon intervenes between the Sun and the Earth and that it covers the Sun. It is what is called “solar eclipse”.

Every time the Moon passes between the Sun and the Earth, a solar eclipse occurs.

But the plane of the ecliptic of the Moon has an inclination of 5º with respect to the Earth’s equatorial plane. This complicates things a bit.

Eclipse
Sun-Earth-Moon system. Credit: web “space-awareness.org”
Moon earth
Lunar orbita round the Earth.  Credit: web “researchgate.net”

The top image shows that the lunar orbit is tilted about 5º from the Earth’s orbit (ecliptic).

Due to this, on numerous occasions (mese) the Moon passes in front of the solar disk but without hiding it.

The diameter of the Sun (1,398,000 km) is 400 times greater than that of the Moon (3,476 km).

But the Moon is 384,000 km from Earth, about 400 times closer than the Sun, which is 150,000,000 km away.

This makes the apparent size of the Moon and the Sun roughly the same.

It is a coincidence that makes it possible for the Moon to completely cover the Sun in certain positions.

Solar eclipses can be total, partial or annular, depending on the proportion of the Sun covered by the Moon.

Eclipse Moon
Lunar eclipse Credit:  web “freepick.es/vector-gratis/”

The shadow that reaches the Earth in a total eclipse is very small, covering at most 270 km wide.

As the Earth rotates and the Moon also moves, the shadow of the Moon moves, in such a way that the eclipse progressively covers the areas near the point of maximum occultation of the Sun.

A total solar eclipse develops in various stages; the result of the progressive darkening is, at times, truly spectacular.

Eclipse sun
Eclipses of the Sun Credit: web “timeanddate.com”

From the most remote antiquity, Chinese (2137 BC) and Chaldean (1375 BC) astronomers recorded some solar eclipse.

The Mayans and Aztecs were also very good astronomers and left us an exact record of the eclipses of the Sun.

The Greek historian Herodotus narrates that when Medes and Lydians were in the middle of a pitched battle, in 585 BC.

There was an eclipse of the Sun that so impressed the combatants that they called off the battle and each retired to their camp.

Interestingly, this eclipse had already been predicted by the Greek philosopher and mathematician Thales of Miletus.

The most famous solar eclipse

Without a doubt, the most famous of all the eclipses of the Sun is the one that occurred on May 29, 1919.

In those years, the theory of relativity enunciated by Albert Einstein was in the focus of all discussions.

According to Einstein, the Sun’s gravitational field bends the light rays (coming from stars) that pass close to its gravitational field. Under normal conditions, there is no way to verify this claim.

There was great anticipation to take pictures of the stars that were in the line of sight close to the Sun during the eclipse.

These photographs would be compared to night photographs of those same stars, when solar gravitation did not affect them directly.

Two teams of scientists specifically traveled to the total eclipse zones to make measurements that would confirm the theory of relativity.

One of these teams, well equipped with instruments and led by the famous English astrophysicist Sir Arthur Eddington (1882 – 1944) made it on April 23, 1919 to Principe Island, on the west coast of Africa, in Guinea.

For a month they spent assembling the complicated observation equipment.

The First World War had just ended, from which Germany, where Einstein was born, had fared very badly.

Eddington was particularly excited that if the results of his measurements confirmed Einstein’s theory, British scientists would have one more reason to reconcile with their German colleagues.

Arthur Eddington
Arthur Eddington  Credit: wikipedia

The other team, led by the English astronomer Frank Watson (1868 – 1939), Director of the Greenwich Observatory, went to the city of Sobral, in the north of Brazil, also to carry out measurements that would demonstrate the then controversial predictions of the theory of relativity.

It is said that in those days Einstein was asked what would happen if the observation did not confirm the predictions of general relativity, Einstein answered something like “then I would be sorry for Sir Eddington and Sir Watson. The theory is correct ”.

Both Sir Watson’s and Sir Eddington’s measurements found that rays of starlight passing near the edge of the Sun were slightly curved.

Thus, the predictions of Albert Einstein’s theory of relativity were fulfilled.

On November 6, 1919, Eddington and Watson published the results of the observations, which were consistent with general relativity.

One day later Einstein was a celebrity, with good reason he is nothing but human genius.

Frank Watson
Frank Watson Credit: Wikipedia

There is a well-known anecdote of Sir Arthur Eddington: a journalist commented to him in relation to general relativity that he was one of the three people in the world who understood it.

With the characteristic sneer of the British, Eddington replied “and who is the third?“.