Mysterious stands of 'angel hair' falling through the sky in Portugal have been caught on camera.
And many residents are questioning whether it's been created by a passing UFO.
One local, who did not want to be named, told the Metro: "It fell during the afternoon. I tried to inquire if aeroplanes flew over before, but no straight answer. It happened two weekends in a row.
"Me and a couple of friends sent it to be analysed – and the weirdest things happened. It reacts to UV light. It comes alive."
According to Wikipedia, angel hair is a sticky, fibrous substance reported in connection with UFO sightings, or manifestations of the Virgin Mary. It has been described as being like a cobweb or a jelly.
It is named for its similarity to fine hair, or spider webs, and in some cases the substance has been found to be the web threads of migrating spiders.
Reports of angel hair say that it disintegrates or evaporates within a short time of forming. Angel hair is an important aspect of the UFO religion Raëlism, and one theory among ufologists is that it is created from "ionised air sleeting off an electromagnetic field" that surrounds a UFO.
More scientific explanations suggest that it's an atmospheric natural phenomenon, or caused by spiders.
Some types of spiders are known to migrate through the air, sometimes in large numbers, on cobweb gliders. Many cases of angel hair were nothing other than these spider threads and, in one occasion, small spiders have been found on the material.
Linyphiidae spiders frequently cause showers of gossamer threads in England and the Northern hemisphere.Australia and New Zealand have frequent cases, caused by several native species of spiders and by some introduced species of Linyphiidae.
Also, atmospheric electricity may cause floating dust particles to become polarised, and attraction between these polarised dust particles may cause them to join together, to form long filaments.
What do you think the angel hair is? Leave a comment below.
Where to go to spot a UFO
UFO? Mysterious 'angel hair' spotted in Portugal sky (video)
Mysterious booming noises and seething balls of light have been spotted above Cradle Hill by visitors scouring the sky for flying saucers. Some say they are attracted by nearby mystical sites such as Stonehenge, sceptics point to the military training grounds on Salisbury Plain. Recently released UFO government files contain flying saucer sightings since the 1950s. For mor info, go to nationalarchives.gov.uk/ufos.
With more than 300 UFO sightings reported every year, this sleepy town is believed to be the world's number one UFO hotspot. It lies at the heart of an area known to UFO enthusiasts as the Falkirk triangle, which stretches between Stirling, Fife and the outskirts of Edinburgh. Visit scotland.org for more.
Alien spaceships and odd sightings have been so regularly spotted on the Black Sea coast that UFO watchers claim that the city could be a galactic hub for aliens. Some people believe that Bytkha Mountain in the area could be a UFO base and one local claims to have taken many photographs.
he Northern Territories claims to have had more UFO sightings than anywhere else in Australia. Unexplained grey and black discs of all shapes and sizes and white and orange lights have been spotted undertaking spectacular manoeuvres as they zip around the skies. Outside Darwin City is the best place to spot them. Visit ufoterritory.com.au.
One of the biggest mass UFO sightings took place during the Stephenville lights incident in 2008 - and sightings have continued. Dozens of people reported seeing a large silent object with red glowing lights flying at high speed in the skies over Stephenville. Some claimed the object was a mile long.
A UFO mecca, thousands of enthusiasts descend on this town to enjoy its four-day Roswell UFO Festival, complete with alien costume competition. The town shot to fame in 1947 when debris from an alleged flying saucer was collected at an army air field. The UFO museum contains research documents and newspaper articles on the incident. Visit roswellufomuseum.com
Radio telescope antennas of the ALMA (Atacama Large Millimeter/submillimeter Array) project, in the Chajnantor plateau, Atacama desert, some 1500 km north of Santiago, on March 12,2013. The ALMA, an international partnership project of Europe, North America and East Asia with the cooperation of Chile, is presently the largest astronomical project in the world. On Wednesday March 13 will be opened 59 high precision antennas, located at 5000 of altitude in the extremely arid Atacama desert. AFP PHOTO/Martin BERNETTI (Photo credit should read MARTIN BERNETTI/AFP/Getty Images)
Known as the UFO capital of the world, the Extraterrestrial Highway is claimed to have more alien and UFO sightings each year than anywhere else. Strangely shaped flying objects and unexplained lights have been reported on the State Route 375 in Sand Spring Valley near Rachel, although non believers attribute them to the Air Force testing base Area 51 nearby.
New Age hippies say that aliens are attracted to this UFO hotspot by the energy emitted by natural earth vortexes in the region. Drawn by its incredible red rock formations, visitors to this spiritual mecca claim to have witnessed amazing celestial displays, frequent UFO sightings and paranormal experiences.
Unidentified orb lights, thought to be flying saucers, were seen by thousands of people over the skies of Phoenix in 1997. The mass sighting became known as the Phoenix Lights. Fresh sightings in 2007 and 2008 were discounted by the military as flares dropped by fighter aircraft.
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10 things we've mistaken for UFOs
UFO? Mysterious 'angel hair' spotted in Portugal sky (video)
This UFO-shaped cloud caused a stir in China when it was spotted hovering in the sky above Jilin Province. The 'lenticular cloud' was pictured moving fast near the Changbai Mountain at the boundary of China and North Korea. After two minutes it was absorbed into a huge cloud cluster and disappeared.
Yes, you read that right. In 2011, a man called 999 to report an unidentified flying object above his house in Hertfordshire. He sounded genuinely panicked and told call handlers blazing lights were coming towards him. Two minutes later the man called back when he realised what he saw was the Moon!
A Swedish diving team found a strange object with "rounded sides and rugged edges" at the bottom of the Baltic Sea in 2011. Some believed that a UFO had crashed into the sea, while others speculated it could be the remains of a World War II German anti-submarine device. Most experts concluded it was most a natural geological formation rather than an "anomalous" object.
This picture shows what looks like the incredible moment a 'UFO' hovered over Seattle. It was in fact the unusual cloud formations around the iconic Space Needle appearing to reveal an alien ship in the sky above the city. But thanks to the building's saucer-like shape it made for a convincing UFO snap.
A rare occurence in 2008 saw Venus, Jupiter and a crescent moon appear together in the night sky from Portsmouth. While planets have been mistaken for UFOs, experts say the sighting was a 'conjunction'. Robert Massey of the Royal Astronomical Society told the Daily Telegraph that "they just appear close in the sky". He added: "I wouldn't be surprised at all if the... police and the [Ministry of Defense] and the [Royal Air Force] get calls about UFO sightings. Because it's a spectacular sight and quite unusual and I think for that reason people really will be struck by it."
Weather balloons are often mistaken for unidentified objects but when they explode they can really look like something that occurs deep in space. When a man from California was scanning the night sky and saw a sudden burst of light through his telescope he was convinced he'd seen a UFO. "I saw another object orbiting this - whatever it was up there, and I’ve never seen anything like that before," Elijah Prychodzko told CBS13. He sent it to a scientist who concluded it was a weather balloon exploding. It was explained as decreasing air pressure causing the rising balloon to expand until it bursts.
Light bouncing off our camera lenses can cause a flare that shows an otherworldly object in our photos and if well placed they can look like alien spacecrafts, like this lens flare that could be a spaceship following a car.
A series of bizarre lights were spotted shining in the sky over Cincinnati in 2012. They were compared to the 1997 Phoenix Lights and after various sightings it was soon revealed that they were not space invaders, but just a group of five skydivers wearing illuminated clothing and performing a pyrotechnics show at a high school event.
These unmanned objects are often deliberately created to look like UFOs to fool people, such as when pizza company Domino's' launched the remote-controlled 'Domicopter'. With more drones in the sky, there have been more UFO reports too. A flying object over a Canadian baseball game in 2013 turned out to be part of a marketing campaign from the H.R. MacMillan Space Center and a camera-mounted drone observing a large crowd of protestors in Moscow was identified as police surveillance. Military drones have also been mistaken for mysterious flying machines - residents in Washington D.C. once thought they had seen UFOs travelling along the Capital Beltway.
One of the most mysterious natural phenomena is ball lightning, which is seen as a flash during a storm and is difficult to capture on camera. Scientists have said ball lightning explains many UFO sightings, like when a green object was seen to roll over the mountains over Brisbane, Australia. Astrophysicist Stephen Hughes told the BBC: "If you put together inexplicable atmospheric phenomena, maybe of an electrical nature, with human psychology and the desire to see something - that could explain a lot of these UFO sightings."