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The alignment of the James Webb Space Telescope has begun, with its camera catching the first photons of light that passed through the telescope.
This means the telescope has achieved the first milestone in a three-month alignment process that will allow humanity to see further into space—and thus further back in time—than ever before.
According to NASA, the arrival of photons at the Near Infrared Camera (NIRCam) instrument marks the first of many steps needed for the telescope to begin capturing images.
At first, these images will be unfocused, but the James Webb team will use them to slowly fine-tune the telescope. Even though the process has just started, NASA has revealed that the initial results match the team's expectations and simulations.
The first images taken by the telescope over the coming months "won't be pretty" like the view of the universe it will provide from this summer onwards, according to NASA. Their purpose is to get the telescope ready for its science mission.
Why Will the Telescope Alignment Take So Long?
The observational power of the James Webb telescope comes from its 6.5-meter (21.3 feet) diameter golden primary mirror. This is composed of 18 hexagonal segments, each of which is 1.32 meters (4.33 ft) in diameter. These segments need to work together and that means matching them to within a fraction of the wavelength of light—about 50 nanometers.
NASA explains this via a comparison: if the primary mirror were the size of the United States, each segment would be the size of Texas. The James Webb team would need to line up the height of those Texas-sized segments with each other to an accuracy of about 1.5 inches.
The mirror alignment and commissioning process will take three months and proceed in seven distinct steps. The first is to align the mirror relative to the spacecraft it sits on.
To do this, the team are pointing the telescope at the bright isolated star HD 84406. The star is pictured by each of the mirror segments, resulting in 18 slightly shifted images, each unfocused and distorted.
The team will move the 18 mirror segments one by one to determine which segment creates which image. After matching the mirror segments to their respective images, the mirrors can be tilted to bring all the images to a common point in an arrangement called an "image array."
In the following steps, this array of pictures will be stacked to produce one unified image. After further phase alignment brings the segments together to act as one unified light-capturing surface, the image quality will be checked across each of the telescope's instruments.
Although the telescope currently has its sights set on HD 84406, located around 242 light-years from Earth, many of its eventual targets will be much further afield.
How Far Can the James Webb Space Telescope See?
The large collecting area of the telescope's primary mirror means it will be able to observe galaxies that are up to 13 billion light-years from us. This doesn't just mean seeing further away in terms of distance, it also means staring further back in cosmic history than ever before.
This is because light takes time to travel across the universe, with a light-year being the distance light can travel through a vacuum in 365 days. The light from these distant galaxies left them many billions of years ago.
Because the universe is expanding, the wavelength of light from distant galaxies is "stretched" towards the red end of the electromagnetic spectrum, a phenomenon called redshift.
The further a galaxy is away, the more redshifted the light it emits will be. This means light from the most distant galaxies is shifted well into the infrared region of the electromagnetic spectrum. This is why the telescope uses the NIRCam to observe the universe in infrared light.
Ultimately, this means capturing a glimpse of the 13.8-billion-year-old universe as it was in its relative infancy. This will give astronomers a picture of the kinds of galaxies that occupied the young universe and how these have evolved to build the cosmic picture we see today.
