The most powerful telescope ever built in human history, James Webb, has captured its first photons of starlight, as it kicks off the three-month-long “alignment process” to be fully ready to reveal new secrets about the universe to us . .
After a 1.5 million kilometer journey to the Lagrange point L2 and the cooling and calibration of its mirror and instruments , achieving this ‘first light’ is an important milestone for any telescope, as it is the point where the observatory and its various instruments detect the light of the stars.
“This is the beginning of the process, but so far the initial results match expectations and simulations,” NASA scientists have explained.
Aligning the telescope is a complicated process divided into seven phases that will take place over the next three months , at which point it will be ready for the instruments to go live. Hence, the first images of the James Webb will not be exactly “pretty”, NASA has warned, since they will only serve to align the telescope.
The seven alignment phases are: Segment Image Identification, Segment Alignment, Image Stacking, Coarse Phases, Fine Phases, Align Telescope Over Instrument Fields of View, and Iterate Alignment for Final Correction.
The first calibration target is a bright star called HD 88406, a star slightly cooler and larger than the Sun (it is about 4.4 times the size of our star), with a surface temperature of about 5000 K. 18 separate, out-of-focus HD 84406 images using each of the mirrors ; with them, an algorithm will determine exactly how each one should be oriented to focus the telescope.
Taking images of this star will allow engineers to create an image of that part of the sky, gradually shifting each of the mirror’s eight individual segments until they see the same image, like an “image array.”
We will have to wait for the first “real” images in May, although those that are released to the public will have to wait until the following month.
