It was just two weeks ago we saw the very first images from the James Webb Space Telescope. The image, well, it was almost unrecognizable as one star. The telescope’s 18 mirrors needed to be aligned and focused. The one star, HD 84406, appeared 18 times in a seemingly random scattering across the image. This was expected, and teams have been working through the alignment process.
Then last week, we got updated imagery. Each of the light points was arranged in a hexagonal pattern corresponding to the mirror segment that reflected that light.
Now, the NASA teams have completed the segment alignment and image stacking, bringing those 18 points of light to one. The progress over the last two weeks is easily evident through the telescope’s imagery:
With the completion of image stacking, Webb has completed the first three steps in the seven-step commissioning process.
- Segment Image Identification ☑
- Segment Alignment ☑
- Image Stacking ☑
- Coarse Phasing
- Fine Phasing
- Telescope Alignment Over Instrument Fields of View
- Iterate Alignment for Final Correction
The next step in the process is course phasing:
Although Image Stacking puts all the light in one place on the detector, the segments are still acting as 18 small telescopes rather than one big one. The segments need to be lined up with each other with an accuracy smaller than the wavelength of the light.
While the big changes made over the last two weeks are important, equally important are the minute changes made to focus and alignment throughout the telescope’s life. While those may not be as flashy in animated gif form, they ensure the sharpness of images as the scope explores the universe.
