UPDATE 2-Ariane rocket launches two space observatories

* Ariane launches two space observatories

* Instruments on board "are revolutionary"

(Updates with details, quotes)

By Laurent Marot

CAYENNE, French Guiana, May 14 (Reuters) - An Ariane rocket launched two scientific space observatories on Thursday that will help scientists better understand the formation of the universe, space officials said.

The rocket blasted off from the European Space Agency's (ESA) launch centre in Kourou, French Guiana on the northeast coast of South America at 10:12 am (1312 GMT).

Twenty-six minutes after lift-off, the rocket released into orbit the Herschel space telescope followed two minutes later by the Planck observatory.

Billed by the ESA as "two of the most sophisticated astronomical spacecraft ever built," the observatories will begin a 60-day journey to the Lagrange point, an orbital slot 1.5 million km (1 million miles) from earth.

"The instruments aboard are revolutionary," Jacques Louet, head of science projects for ESA, told Reuters at the Kourou launch site on Wednesday.

"They will be using technologies that have never been applied," he said.

LARGEST MIRROR IN SPACE

Herschel has the largest mirror of any space telescope now in orbit. Its 3.5-m (11.5 ft) diameter primary mirror is one-and-a-half-times the size of the Hubble Telescope's main reflector.

The spacecraft is a far-infrared and sub-millimetre telescope which will investigate how stars and galaxies form and how they evolve.

By studying infrared light, it will be able to see through clouds of dust that currently obscure astronomer's view of star and galaxy formation, to illuminate the processes behind them.

It also will examine the dust ejected by dying stars, which spread the heavy elements necessary for life through the universe, and will analyse the composition of comets and planets the solar system.