NASA's James Webb telescope opens its 'golden eye' mirror

NASA's new space telescope opened its huge, gold-plated, flower-shaped mirror on Saturday, the final step in the observatory's dramatic unfurling.

The last portion of the 6.5-metre mirror swung into place at flight controllers' command, completing the unfolding of the James Webb Space Telescope.

"I'm emotional about it. What an amazing milestone. We see that beautiful pattern out there in the sky now," said Thomas Zurbuchen, NASA's science missions chief.

More powerful than the Hubble Space Telescope, the $10-billion US Webb will scan the cosmos for light streaming from the first stars and galaxies formed 13.7 billion years ago.

To accomplish this, NASA had to outfit Webb with the biggest and most sensitive mirror ever launched — its "golden eye," as scientists call it.

Webb is so big that it had to be folded origami-style to fit in the rocket that soared from South America two weeks ago.

The riskiest operation occurred earlier in the week, when the tennis court-size sunshield unfurled, providing subzero shade for the mirror and infrared detectors.

Primary mirror began opening Friday

Flight controllers in Baltimore began opening the primary mirror on Friday, unfolding the left side like a drop-leaf table.

The mood was even more upbeat on Saturday, with peppy music filling the control room as the right side snapped into place. After applauding, the controllers immediately got back to work, latching everything down. They jumped to their feet and cheered when the operation was finally complete two hours later.

"We have a deployed telescope on orbit, a magnificent telescope the likes of which the world has never seen," Zurbuchen said, congratulating the team. "So how does it feel to make history, everybody? You just did it."

His counterpart at the European Space Agency, astronomer Antonella Nota, said that after years of preparation, the team made everything look "so amazingly easy."

"This is the moment we have been waiting for, for so long," she said.

Webb's main mirror is made of beryllium, a lightweight yet sturdy and cold-resistant metal. Each of its 18 segments is coated with an ultra-thin layer of gold, highly reflective of infrared light.

The hexagonal, coffee table-size segments must be adjusted in the days and weeks ahead so they can focus as one on stars, galaxies and alien worlds that might hold atmospheric signs of life.

Webb should reach its destination 1.6 million kilometres away in another two weeks; it's already travelled more than one million kilometres from Earth since its Christmas Day launch. If all continues to go well, science observations will begin this summer.

Astronomers hope to peer back to within 100 million years of the universe-forming Big Bang, closer than Hubble has achieved.