This morning observers across Europe were treated to a rare solar eclipse as the moon passed across the face of the sun and obscured it almost entirely from view. But while many, in the UK especially, had to contend with clouds, plenty of images captured the event – and an odd black spot on the sun. While it might have looked like a speck of dust at first, this was actually a sunspot on the solar surface, caused by a concentration of magnetic fields. Scroll down for video . People in the UK were treated to a partial solar eclipse this morning. But several observers spotted some strange black dots on the sun (shown). These were sunspots, caused by concentrations of magnetic fields. They are sometimes associated with eruptions such as solar flares . Sunspots are fairly common, with the number on the surface correlating with how active the sun is. They occur when a concentration of magnetic fields causes the surface temperature to reduce, making a specific section stand out from the surroundings. They range hugely in size, from just 10 miles (16km) to 100,000 miles (160,000km) - big enough to be seen from Earth without a telescope, and more than ten times the size of our planet. Sunspots are regions where powerful magnetic fields emanate from the sun . These magnetic fields can get wound up so tightly that they rise up from inside the Sun, and the sunspots mark the points where this happens. They are much colder than the rest of the sun's surface and usually last a few days before disappearing. They have a temperature of anywhere from 2,700 to 4,200°C (4,890 to 7,590°F), compared to 5,500°C (9,930°F) for the surrounding solar material, which is why they are so visible. Sunspots are also sometimes the source of eruptions on the sun, namely solar flares and coronal mass ejections (CMEs), all of which are linked to magnetic fields. The sun goes through a periodic change in activity known as a solar cycle, which has an average duration of 11 years, which also changes the frequency of sunspots. Sunspots should not be confused with coronal holes, regions of the corona - an aura of plasma around the sun - where the magnetic field reaches out into space rather than looping back down onto the surface. Sunspots (previous Nasa image shown) are fairly common, with the number on the surface correlating with how active the sun is. They occur when a concentration of magnetic fields causes the surface temperature to reduce, making a specific section stand out from the surroundings . Some observers took to Twitter to express their views on the sunspots, which were spotted in live footage showing the moon passing across the face of the sun . Others bemoaned the cloud coverage in the UK, which meant that many observers were unable to actually see the event at all. There were more than 10,000 mentions of the eclipse per minute on Twitter, according to social media monitoring company Brandwatch . The sun goes through a periodic change in activity known as a solar cycle, which has an average duration of 11 years, which also changes the frequency of sunspots. In this Nasa image, multiple sunspots can be seen across the solar surface . This morning, millions across Britain stopped to watch the country's first solar eclipse this century, which plunged parts of the UK in to brief darkness. Astronomer Gemma Lavender from All About Space magazine explains: . 'When a solar eclipse occurs, what you’re witnessing is Earth, moon and the sun aligning. 'Eclipses can only really happen at a new moon. With this in mind, it’s quite easy to think that we should get an eclipse every month but because the moon’s orbit around  Earth is tilted by around five degrees to that of our planet’s, our natural satellite’s shadow usually misses the Earth’s surface by passing above or below it. 'It’s only really at least twice a year that the geometry lines up just right to make an eclipse for observers in a particular part of the world. 'The sun is roughly 400 times bigger than the moon but it is also around 400 times further away from us. As a result, the sun and the moon have the same size in the sky to make a partial or total eclipse. 'There are two types of eclipse - a partial and a total. During a partial solar eclipse, only some of the sun’s surface gets blocked out by our lunar companion. 'With a total eclipse, all of the Sun’s surface gets covered by the moon, creating a shadow that is projected onto  Earth. Day turns into darkness for a few minutes for observers in this shadow. 'However, when the moon passes in front of the sun, we don’t always get a total eclipse. 'Instead, we get an annular eclipse, also known as a ‘ring of fire’ - that’s when the Moon is at a further distance from the Earth in its orbit and therefore appears smaller, unable to cover the Sun’s disc entirely. 'At a distance of around 220,000 miles (357,000 kilometres) on 20 March though, the sun’s disc was sufficiently covered.' Britain's skies began to darken at around 8.24am this morning as the moon started to move between us and the sun, with the eclipse peaking at around 9.30am across the country. The sun's light was almost totally concealed, casting a huge shadow of the moon across the nation turning day briefly to night, but watchers could not look directly at the sun because they risked damaging their eyes. In the Hebrides the sun was practically invisible as the Isle of Lewis experienced a 98 per cent eclipse, while the Faroe Islands saw a total eclipse. But cloud coverage meant that millions across Britain were unable to see anything at all of the eclipse, the like of which will not be seen again for several more decades. The last solar eclipse of such significance occurred on August 11 1999, and was 'total' - with 100 per cent of the sun covered when seen from Cornwall. Another 'deep' partial eclipse visible in the UK will not occur until August 12 2026, and the next total eclipse not until September 2090. Today's eclipse produced a 100-mile-wide 'totality' shadow path that crossed the North Atlantic and covers only two land masses, the Faroe Islands between Scotland and Iceland and the Norwegian archipelago of Svalbard. Away from this path the sun was partly obscured. A partial eclipse was visible across a large part of the northern hemisphere, including the whole of Europe, Greenland, Newfoundland, northern Africa and western Asia. More than 100 people flocked to the 5,000-year-old Callanish Stones on the Isle of Lewis to witness the solar eclipse. And they were rewarded most of the time by a break in the clouds - almost to the point of near totality. Lewis had been billed as the prime place in Britain to see the solar phenomenon. Caroline Pritchard, 58, and her partner Laurence McCallum, 50, travelled 905 miles in a 21 hour car and ferry journey - together with their three dogs - to see the event. This morning, millions across Britain stopped to watch the country's first solar eclipse this century, which plunged parts of the UK in to brief darkness . 'This is the end of the age of Aquarius and we wanted to get here to see the eclipse,' said Mr McCallum, who works in a fine food business. 'I took the week off work unpaid and it has been worth it. It was fantastic. We arrived on Tuesday and unfortunately missed the other great astronomical event here this week - the Northern Lights. But the eclipse more than made up for it.' Ms Pritchard agreed: 'I am a spiritual person and I was drawn here to see the eclipse. I believe in powers greater than ourselves.' Islander Linda Vaughan, 62, from Crossbost, rang a Tibetan bowl to herald the eclipse as it created dusk - with temperatures noticeably plunging with the sun's infra red blocked out. 'The sound resonates with the stones. This is a spiritual and sacred place.. It is about creating the right harmony,' she said. The sun's light was almost totally concealed, casting a huge shadow of the moon across the nation turning day briefly to night, but watchers could not look directly at the sun because they risked damaging their eyes. Instead, solar eclipse glasses (shown) helped people observe the event . Four intrepid shadow seekers even boarded a special boat trip with Kilda Cruises from Leverburgh on the Isle of Harris at 5am to witness the eclipse at remote St Kilda. The archipelago, 41 miles (66km) west of the main Outer Hebrides, was forecast to be cloud free at the time of the event. Donny Mackay, president of the Stornoway Astronomical Society, said it received over 500 inquiries by email - as well as 100 phone calls - from all over the UK as well as far away as Germany. 'I was a bit worried when I saw the cloud early this morning but it turned out as good as we could have hoped for. It was really memorable,' he said.
People in the UK were treated to a partial solar eclipse this morning . But several observers spotted some strange black dots on the sun . These were sunspots, caused by concentrations of magnetic fields . They are sometimes associated with eruptions such as solar flares . And they can be more than ten times as big as Earth .