The unknown bright object flashing across the sky at Heathrow Airport.Youtube/AIRLIVE net

A video, filmed in Australia, captured a monster UFO "the size of the Earth" before it mysteriously disappeared. The video showing the UFO appears in the sky to explore the surroundings.

According to reports, the UFO "horrified onlookers," who watched the mysterious object hovering above the sky in Australia. The video with title "Earth-Sized UFO Sighted in Australia" shows the object moving into the Sun.

"Planet-sized UFO starts moving about and finally moves into the Sun. Another smaller UFO has sighted also," the video description stated.

According to Daily Star, the mysterious object appears to hide behind the Sun before a blinding light blocks the camera view. Some onlookers also believe that the blinding light was an explosion by an alien craft. The object then suddenly flits away.

Onlookers claimed that they have seen such lights before. "I saw something that looked very similar around this time last year," one YouTube user said.

Another user claimed that it is just swamp gas.

However, Scott Brando, a sceptic, who runs debunking website ufoofinterest.org claimed that the object in the video is nothing but a reflection of the sun.

"That 'UFO' is just the solar disc (of the Sun) reflected through the glass," Brando told Express.co.uk.

Mick West, the administrator of the Metabunk.org website, said that another video claimed to have shown a "second sun."

"However analysis of the video proves that what is shown is an offset lens reflection of the Sun itself. There is nothing else in the sky. The effect is also not a sun-dog, an atmospheric reflection, or a mirage. It's just a reflection happening at the camera. We can see this quite clearly if we stabilise the video so the background is fixed," West said.