The telescopes will detect infrared and microwave radiation respectively – revealing the birth of stars and galaxies, and the structure of the universe shortly after the big bang

Two of the most sophisticated spacecraft ever built – Herschel and Planck – have been launched from Europe's spaceport in Kourou, French Guiana, on top of an Ariane 5 rocket.

The European Space Agency's two telescopes are destined for a point beyond the moon's orbit. From there, they will begin observations that will improve our understanding of the history of the universe.

Herschel will study some of the coldest objects in space in the far infrared, a part of the electromagnetic spectrum still mostly unexplored. Planck will map the "fossil light" of the Universe - microwave radiation left over from the big bang – with unprecedented sensitivity and accuracy. The two missions are among the most ambitious ever carried out by Europe.

When Herschel and Planck have separated shortly after launch they will head independently towards the L2 Lagrangian point of the Sun-Earth system – a gravitational stability point some 1.5 million kilometres from Earth in the opposite direction to the sun.

They will orbit the sun in the Earth's shadow, allowing them to conduct continuous observations in a thermally stable environment far from any radiation disturbance from the Sun, Earth or moon.

Herschel is the largest infrared telescope ever launched. The extremely smooth surface of its 3.5m primary mirror is nearly one and a half times as large as Hubble's optical mirror, and six times as big as its infrared predecessor ISO, launched by Esa in 1995.

With its huge light-collection capability and set of sophisticated detectors cooled to within a whisker of absolute zero by around 2,000 litres of superfluid helium, Herschel will look at the faintest and farthest infrared sources and peer into the as-yet uncharted far infrared and submillimetre parts of the spectrum.

It will be able to see through cosmic dust and gas to observe events that date from the early universe, such as the birth and evolution of stars and galaxies 10 billion years ago. Closer by, within our galaxy, Herschel will also observe extremely cold objects, such as the clouds of dust and interstellar gases from which stars and planets are formed, and even the atmosphere around comets, planets and their moons in our own solar system.

Meanwhile, Planck will measure tiny temperature fluctuations in the very early Universe with unprecedented sensitivity. It will monitor the cosmic microwave background, the relic of the very first light ever emitted in space about 380,000 years after the big bang, when the density and temperature of the young universe had decreased enough to finally allow light to separate from matter and travel freely in space.

Herschel's detectors will be cooled to 0.3 degrees above absolute zero. But Planck's detectors will reach even colder temperatures, just 0.1 degrees above 0 K. Esa says that during its mission, the coldest points of the universe may well be its instruments. The satellite will help astronomers to create a set of multi-million-pixel sky maps that will reveal the universe's structure. It will be able to determine the total mass of atoms in the Universe, infer the total density of the mysterious dark matter and even shed new light on the nature of dark energy.