Astronomers have spotted two monster galactic clusters slamming together in one of the biggest collisions ever recorded.

The smash-up poses no danger to Earth -- it is about 800 million light-years away, and the galaxies involved tend to speed by each other without crashing -- but the Milky Way could be on a similar collision course in a few billion years.

"Today's cosmic weather report shows a cosmic storm that is one of the most massive objects in the universe," J. Patrick Henry of the University of Hawaii, who led an international scientific team to make the observation, said in a telephone news conference. "The long-term forecast is for fair weather, about 7 billion years in the future."

The violent merger offers the best data yet on the process, which could help scientists learn more about how galaxies and their contents developed in the early universe.

At 800 million light-years away, the crash site is considered relatively close. The crash itself extends about 3 million light-years across. A light-year is about 6 trillion miles, the distance light travels in a vacuum in a year.

The larger of the two galactic clusters probably contains 1,000 galaxies, while the smaller one has 300 or so. The Milky Way does not belong to a galactic cluster; it is part of a group located on the outskirts of the Virgo cluster, which is about the same size as the smaller component of the big collision.

Henry and his colleagues believe that the two galactic clusters were separate objects about 300 million years ago and began slamming together after that.

The scientists captured information on the merger with the European Space Agency's XMM-Newton observatory.

Astronomers have known for decades that two clusters of galaxies were merging in the area of the sky near Hydra (the Water Serpent), and dozens of other such colliding galactic clusters have also been identified.