Rejoice, all ye astronomers. Because after years of delays and billions of dollars in overruns, the components of NASA’s James Webb Space Telescope (JWST) are finally complete. It’s been a long time coming.

The space telescope's huge new primary mirror, the biggest ever built, was unveiled yesterday at NASA’s Goddard Space Flight Center in Maryland. With its 18 gold-plated hexagonal mirrors measuring 6.5 meters (21.3 feet) across, it will have 100 times the observing power of Hubble when it launches in 2018.

Also this week, it was announced that construction of the vast tennis court-sized sunshield that will protect the telescope's optics from the Sun's rays was complete. After further testing, the mirror and sunshield will eventually be integrated together.

“Upon completion, Webb will be the largest and most complex space observatory that anyone on planet Earth has ever built,” said NASA Administrator Charlie Bolden in a statement.

“It will capture the imagination and dreams of millions who dare to look to the sky and wonder.”

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When it is launched in October 2018, the JWST will be positioned beyond the orbit of the Moon in a region of gravitational stability called Lagrange point 2, or L2. From here, it will have a glorious unobstructed view of the cosmos, returning stunning views of the universe.

Although it’s billed as the successor to Hubble, it’s somewhat different in that it will observe the universe in infrared, rather than visible like Hubble. But its size will afford it greater views of galaxies, stars, and even exoplanets than we’ve had before.

Its infrared capabilities will allow it to peer through cosmic dust into galaxies and planetary systems. Its 18 mirrors will all work together to capture these views.

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The JWST was originally projected to launch by 2011 at a cost of as little as $1 billion. Various delays, though, have seen that spiral to $8.7 billion with a launch seven years later. Thus, the actual launch itself is bound to be nerve-racking. Owing to its distance, it cannot be serviced once it is in space, unlike Hubble, which had numerous manned repair missions to fix faults and upgrade it.

In addition to construction being complete, it was also announced yesterday that the JWST had completed a Center of Curvature test, which essentially tested the telescope's optics. Now, there will be months of further testing to ensure the telescope can withstand the pressures of launching.

The JWST has been under construction for more than 20 years. With this latest news, finally, we’re one step closer to this amazing space observatory becoming operational.