Move over Hubble: Why the James Webb Space Telescope is such a big deal

It's been decades in the making and has faced more than its fair share of delays, but if all goes as planned, the James Webb Space Telescope will launch within the coming days.

Astronomers have been eagerly anticipating the launch of this telescope — and with good reason.

The $10-billion telescope is the largest and most powerful ever sent into orbit. Building upon the discoveries of the famed Hubble Space Telescope, it will peer back into a time when our universe was in its infancy and will also reveal much more about the atmospheres of exoplanets.

As of now, the telescope — also known as JWST or just Webb — is expected to launch on Dec. 25 from French Guiana.

The light of everything we see in the night sky takes time to travel to Earth. The moon's light takes just over a second to get to us, while the sun's light takes roughly eight minutes.

The farther away an object is, the longer it takes for its light to reach us, so everything we see is as it was, not as it is. That means, essentially, when we look at distant stars and galaxies, we're looking back in time.

Telescopes allow us to see further back in time by collecting faint light, which is why they're often called "light buckets" by astronomers. The bigger the telescope, the more light it can collect and the further back it can see.

While ground-based telescopes work the same way, they must deal with atmospheric disturbances, which makes them less desirable than space-based telescopes, which are above Earth's atmosphere.

Most people are familiar with the Hubble, launched into orbit in 1990. This workhorse of a telescope has not only provided incredible insight to astronomers about the beginnings of our universe, but has also given us jaw-dropping images of planets, galaxies, nebulas and spectacular clusters of stars. 

While people sometimes refer to the James Webb Telescope as being a replacement to Hubble, it's more like a younger, stronger brother.

Webb is bigger than Hubble, with new capabilities that will allow us to see the universe from about 100 million to 250 million years after the Big Bang. In essence, we are looking back in time to when the universe was in its infancy.

For comparison, Hubble is big, about the size of a school bus — but Webb is about the size of a tennis court. Hubble's mirror, which collects light from distant objects, is 2.4 metres in diameter. But Webb's light-collecting ability is far superior, comprising 18 separate mirrors that will unfold once in orbit, for a total diameter of 6.5 metres.

There's also a difference in the way in which both telescopes look at the universe.

Hubble mainly sees the universe in visible or optical light, detectable by the human eye, though it can also operate in ultraviolet and near-infrared wavelengths.