Since the launch of the James Webb Space Telescope in December last year, engineers have been working to deploy the telescope’s hardware, then align both its mirrors and its instruments. Now, that months-long process is complete, and the telescope is confirmed to be fully aligned. NASA and the European Space Agency have shared an image showing the sharpness check of all of Webb’s instruments, showing that they are all crisp and properly focused.
“Engineering images of sharply focused stars in the field of view of each instrument demonstrate that the telescope is fully aligned and in focus,” the European Space Agency writes. “For this test, Webb pointed at part of the Large Magellanic Cloud, a small satellite galaxy of the Milky Way, providing a dense field of hundreds of thousands of stars across all the observatory’s sensors. The sizes and positions of the images shown here depict the relative arrangement of each of Webb’s instruments in the telescope’s focal plane, each pointing at a slightly offset part of the sky relative to one another.”
The four instruments in question are the Mid-Infrared Instrument (MIRI), the Near-Infrared Camera (NIRCam), the Near-Infrared Spectrograph (NIRSpec), and the Near-Infrared Imager and Slitless Spectrograph/Fine Guidance Sensor (NIRISS/FGS). Those are three imaging instruments and one spectrograph (an instrument for detecting the composition of objects by separating the light they give off), but the spectrograph can be used to take images as well — like the images shown above which are used for calibration and target selection. If you look at the NIRSpec image you’ll see black bands across it, which are caused by its microshutter array which allows it to open and close tiny windows so that the instrument can observe up to 100 objects at the same time.
All four of the instruments are pointed at the same target so that engineers could check they were all as sharp and accurate as they need to be. And the results are even better than the engineers hoped, resulting in a high degree of image quality which means the instruments are diffraction-limited — meaning that they are getting the maximum amount of detail possible for the size of the telescope.
With the alignments complete, now the team can begin commissioning each instrument. That involves configuring and checking parts of the instruments such as the masks and filters to make sure they are ready for science operations. There are also some final telescope calibration processes required, like checking that the telescope remains at a steady temperature when moving from one target to another. Once all of this is done, the telescope is scheduled to begin science operations this summer.
