After entering its final orbit around the second Sun-Earth Lagrange point, otherwise known as L2, about 1.5 million kilometers (nearly a million miles) from Earth, NASA’s James Webb Space Telescope recently detected its first photons. This is a major milestone in a nearly two-decades-long project. On February 3, the first light particles made their way through the entire telescope. Webb is now as close as ever to its primary goal of studying the early universe and capturing stunning photos of deep space unlike anything we’ve seen before.
The onboard Near Infrared Camera, one of four cameras on Webb, confirmed the achievement just a few days after being switched on. Capturing its first photons is a critical step toward full imaging operations. Using initial readings, scientists can begin working to align the telescope’s 18 mirrors to ensure precise, accurate measurements and photos.
‘We had model and computer simulations of what we would see when we pointed at specific places in the sky and the actual data looks very similar to the simulations,’ a NASA spokesperson told Inverse.
✨ Our NIRCam instrument’s detectors saw their 1st photons of starlight! While #NASAWebb is not yet ready for science, this is the first of many steps to capture images that are at first unfocused, used to slowly fine-tune the optics: https://t.co/Sak6r7Ncex #UnfoldTheUniverse pic.twitter.com/vHRX8x9ki2
— NASA Webb Telescope (@NASAWebb) February 3, 2022
Aligning the telescope will take about three months, and it all begins with early, unfocused photos. As NASA puts it, photos captured during the preparatory phase will not be ‘pretty.’ Alignment is aided by algorithms the team developed using a 1/6 scale model telescope testbed. Of course, simulations and reality don’t always line up, but so far so good.
The space telescope includes 18 primary mirror segments, all of which need to be aligned so they can work together as a single mirror. NASA writes, ‘the telescope’s 18 primary mirror segments need to match each other to a fraction of a wavelength of light – approximately 50 nanometers.’ To put it another way, if the Webb primary mirror is the size of the United States, each mirror is about the size of Texas, and the Texas-sized segments must line up with each other to an accuracy of under 4cm (1.5″).
The alignment process includes seven primary steps: segment image identification, segment aligning, image stacking, coarse phasing, fine phasing, telescope alignment over instrument fields of view, and iterate alignment for final correction. You can read about each step in detail by clicking here. As part of the alignment process, the telescope is pointed at a bright, isolated star (HD 84406). The telescope captures a series of images that are then stitched together. At first, each of the 18 mirrors is tilted slightly differently, so there are 18 slightly shifted photos of the same star. Each one is uniquely out of focus and shifted. These initial segment images will inform the scientists here on Earth about moving each mirror.
Scientists will be studying many different fuzzy images over the next few months. Once all the mirror segments are aligned and the instruments pass final tests, the James Webb Space Telescope will begin the work it has been designed for, finding out more about the galaxies that formed in the early universe and studying planetary formation. It has been nearly 20 years in the making, but the $10B project is clearing its final hurdles to begin its critical and exciting science operations. We will see our first beautiful photos captured by Webb this summer if all goes according to plan.