A spectacular comet will outshine the moon in one of the most dazzling displays ever seen on Earth, according to scientists working on Nasa's Hubble telescope.
Images of Comet Ison, a four-mile wide clump of frozen gas and dust with an icy nucleus and a 57,000-mile tail, have been captured by Hubble operators as it streaks through space at 48,000mph on a course to pass the Sun later this year.
The comet is expected to provide astronomers with new data into conditions at the furthest reaches of our solar system. Comet Ison is thought to be on a trajectory from the Oort Cloud, which scientists believe to be a zone of frozen debris 18 trillion miles from the sun, left over from the birth of the solar system four billion years ago.
"Comet Ison is potentially the 'comet of the century' because around the time it makes its closest approach to the Sun, on 28 November, it may briefly become brighter than the full moon," said Ray Villard of the Space Telescope Science Institute, which operates the Hubble programme.
Minute dust particles from its tail could create an invisible rain of cosmic dust over the Earth, while the phenomenon of "noctilucent clouds" could turn the night skies blue over the poles, according to reports.
At its closest approach to Earth on 26 December, the comet will be nearly 40 million miles away, providing what is forecast to be a spectacular firework display visible on Earth to the naked eye for several weeks, even in daylight.
However, the sun's heat could cause the comet to disintegrate altogether, though scientists say its survival prospects appear "promising".
Amid growing excitement in the astronomical community, Nasa released its images to coincide with the 4 July celebrations in the US.
Commenting on the sequence, a Nasa official said: ""The movie shows a sequence of Hubble observations taken over a 43-minute span and compressed into five seconds.
"Its skyrocket-looking tail is really a streamer of gas and dust bleeding off the icy nucleus. The pressure of the solar wind sweeps the material into a tail, like a breeze blowing a windsock.
"The deep-space visitor streaks silently against the background stars. In this brief video, the comet travels 34,000 miles, or 7% of the distance between Earth and the moon."