James Webb Space Telescope snaps first images – a star and a selfie
The James Webb Space Telescope has taken its first images of space. What looks like a smeared starfield is actually the same star snapped 18 times, as the mirror segments try to align themselves to focus on the star. The craft also took a selfie of its mirrors to help align them.
The JWST is made up of a tennis court-sized array of 18 golden mirrors, but after launch and deployment, they’re all pointing in slightly different directions. Before the telescope can begin probing the depths of the cosmos, these mirrors need to be brought into alignment so they can focus on the same object.
The first such object is a star known as HD 84406, located in the constellation Ursa Major. It was selected for this calibration job because it’s bright and isolated from other stars, making it easy to identify. To find it, the telescope was pointed to 156 different positions around the predicted location – an area of sky about the size of the full Moon – generating 1,560 images. Then, the data was scanned until the star had been located in images from all 18 mirror segments. These 18 images were then stitched together into one mosaic.
From this data, the team can determine the alignment positions of each mirror segment. Over the next few weeks, the positions of the mirrors will be adjusted until the 18 stars merge into one.
“Launching Webb to space was of course an exciting event, but for scientists and optical engineers, this is a pinnacle moment, when light from a star is successfully making its way through the system down onto a detector,” said Michael McElwain, a project scientist for the JWST.
Another perspective will help with this alignment process. A lens inside the NIRCam instrument is pointed back towards the primary mirror segments, allowing the spacecraft to take selfies for engineering purposes. In this shot, the bright segment is currently pointed towards the star, while the others aren’t in the same alignment.
These images constitute major milestones in James Webb’s progress, but aesthetically they’re pretty underwhelming. The real money shots will arrive mid-year, after all the alignments are complete and the instruments are cooled to their cryogenic operating temperatures.
The team describes the alignment process in the video below.