James Webb First Images Explained as Telescope Exceeds NASA's Expectations

The James Webb Space Telescope has sent back its most detailed image yet, less than three months after its launch in late December.

On Wednesday, NASA said it had reached a new milestone in its efforts to set up the state-of-the-art telescope's optical system as it prepares for its first scientific observations in the summer.

The new image shows a single, bright star against a backdrop of other, dimmer stars and galaxies in the far distance. The image appears in red because of the filter the Webb team were using.

New James Webb image
A photo of a star against a backdrop of galaxies taken by the James Webb Space Telescope. It shows that the telescope's mirror alignment has gone well so far. NASA/STScI

The image may not be comparable to the sweeping, dramatic images of the cosmos that we're used to from Hubble or other space telescopes, but this single star image is a crucial step for Webb.

In order to capture the light needed to take images, Webb uses 18 hexagonal mirror segments that must all be perfectly aligned so that they effectively operate as one big mirror. These segments collect light from space and then direct it to Webb's delicate optical instruments in order to produce an image that we can see.

If the 18 mirror segments aren't perfectly aligned, Webb can't take photos properly. A good example of this is in the very first image taken by Webb in February, which showed 18 points of light scattered around a black background.

James Webb telescope's first photo
The first photo taken by the telescope, showing its scattered view of one single star. NASA

These 18 points of light are actually all one star. The problem is that when the photo was taken, each of Webb's 18 mirrors were not aligned and were effectively acting as 18 separate telescopes, Lee Feinberg, Webb Optical Telescope Element Manager, said in a NASA video at the time.

Since then, the scientists working on Webb have carefully positioned each of the mirrors so that they act as one. This process can be seen in this image from NASA, which shows how the scattered points of light in the first photo were then organized into the hexagonal shape of Webb's mirrors. These points of light were then "stacked" so that they became one, single star image.

That's why the most recent Webb image released this week is important—it shows one single star.

"We have fully aligned and focused the telescope on a star, and the performance is beating specifications," Ritva Keski-Kuha, deputy optical telescope element manager for Webb at NASA Goddard, said in a statement. "We now know we have built the right telescope."

But there is lots more work to do. In the coming weeks and months the scientists behind the telescope must go through the rest of the alignment process, which is on track for completion in early May, and then fully prepare its scientific instruments.

James Webb star alignment image
An organized image of the same star as seen by each of James Webb's 18 mirror segments. The image was then overlapped to show a single star. NASA/STScI/J. DePasquale