Solar eclipse: the five stages, what time it is, how long it lasts. Everything you need to know about this astronomical phenomenon

The eclipse taking place this evening will be the first total solar eclipse on the European continent since 1999, excluding those of 2006 and 2015, which affected parts of Georgia and Russia, and the Faroe Islands and Svalbard respectively. This rare and eagerly awaited event will take place shortly before sunset and will also be visible, albeit partially, from Italy: it will begin at around 7.30 pm – Italian time – with the Sun already low on the horizon and nearing sunset, reaching the intermediate phase at around 7.50 pm and its peak at 8.20 pm. In Italy, therefore, the Moon’s disc will be seen gradually covering the Sun, but the corona will not be visible, not even at the peak of the event. The regions with the best viewing conditions are those in the north and west: Piedmont, Valle d’Aosta, Liguria, Lombardy, Emilia-Romagna, Tuscany and Sardinia, where the solar disc will be obscured by 90 per cent or more, whilst the regions of central and southern Italy will experience the phenomenon to a much lesser extent. Unlike a total eclipse, during a partial eclipse the Sun is never completely obscured and the solar corona is not visible, not even at the peak of the event.

Tonight’s eclipse will therefore pass over Greenland, Iceland and Spain, where the umbra will leave Earth at sunset, just beyond the Balearic Islands, over the Mediterranean, and will serve as a foretaste of the even more spectacular eclipse due to take place next year – one of far greater significance, with a total phase lasting nearly six and a half minutes, among the longest of the century. Today’s eclipse will cross a narrow strip of land and sea stretching from Arctic Russia, passing through Greenland, touching parts of the far west of Iceland, a tiny portion of Portugal and a wide swathe of Spain. The total phase will not last long – between one and a half and two minutes – exceeding two minutes only off the Icelandic coast and in certain parts of Greenland. To mark the occasion, the European Space Agency is organising a live stream of the event starting at 7.30 pm, which you can follow by clicking on this link.

Today’s total eclipse will therefore consist of five phases. The first is the moment when the Moon’s disc begins to overlap with that of the Sun, and this will continue for around thirty minutes; the second will be one of the most spectacular, during which a sort of ‘diamond ring’ will be visible in the sky, because beams of light will be produced whilst the last fragment of the Sun’s disc is still visible. Immediately afterwards, totality will begin – an early night that will last a maximum of 2 minutes and 18 seconds, depending on the location from which it is observed. Then we will once again be able to see brilliant ‘pearls of light’ around the lunar disc, and finally the Moon will slowly reveal the Sun once more. However, from Italy it will not be possible to witness all five phases because, not only – as we have already mentioned – will totality not be visible anywhere in the country, but also because the phenomenon will occur at a time very close to sunset.

A solar eclipse occurs when the Moon passes directly between the Sun and the Earth, casting a narrow band of shadow onto our planet. During the totality phase, a sort of twilight sets in, the temperature drops and some animals may alter their behaviour. The phenomenon is made possible by a particular coincidence: the Sun is about four hundred times larger than the Moon, but it is also about four hundred times further away from Earth. For those in the right position, therefore, the two celestial bodies appear to be of similar size and the Moon is able to completely cover the Sun’s disc, revealing the corona, the outermost part of the Sun’s atmosphere. The partial phases, from the start to the end of the Moon’s passage in front of the Sun, will last around one hour and 45 minutes. A partial eclipse will also be visible across much of Europe, Canada, the northern United States and north-western Africa. The difference compared with a total eclipse is, however, enormous: even with just 1 per cent of the Sun still visible, its brightness remains around four thousand times greater than that of a full Moon, explained Alain Doressoundiram, an astrophysicist at the Paris Observatory.

On average, one or two solar eclipses occur each year, but the part of the world where totality can be observed is very narrow. A given area of the Earth may therefore have to wait around four hundred years before witnessing the phenomenon again. The next total eclipse, on 2 August 2027, will cross southern Spain, North Africa and the Arabian Peninsula, with a totality lasting up to six minutes and 23 seconds. A longer eclipse will not occur until 2114.

The solar eclipse taking place this evening before sunset poses no direct risk to human health – such as effects on pregnancy or nutrition – with the sole exception of permanent damage to the eyes caused by looking directly at the sun, even for a short time. The Ministry of Health has published a series of recommendations on this matter. Before observing the eclipse, it is essential first of all to wear specific eye protection – sunglasses are not sufficient – and to keep them on at all times. The primary risk is damage to eyesight: looking directly at the sun or a solar eclipse, even for a short time, can cause permanent damage to the retina – known as solar retinopathy – without causing any immediate pain. The risk is increased in the case of repeated observations, even if brief. The damage may become apparent hours or days later.

There is only one safe way to view the eclipse directly: look at the sun using special eclipse glasses that are certified to meet the ISO 12312-2 standard. Any other method must be avoided as it does not always guarantee safe protection: as mentioned earlier, sunglasses are not sufficient, nor are X-ray film, homemade filters, welder’s goggles, camera lenses or anything else. Children and young people are at greater risk, as their eyes are more easily damaged and because the fascination of the phenomenon may draw them towards looking at the sun. For them, observing the eclipse should take place under the constant supervision of adults, who must ensure that children and young people wear the appropriate glasses at all times. Older people, those with pre-existing eye conditions, or those who have undergone certain eye surgeries may be at greater risk.