NASA engineers are at the Space Telescope Science Institute in Baltimore, Maryland, aligning the mirrors and instruments on the James Webb Space Telescope. The mission team has provided us with another glimpse of what this observatory will look like once it is fully operational. There is atelescope alignment evaluation image of a distant star that looks red and spiked.
The completion of the fifth phase of preparation, known as fine phasing, where the mission controllers adjusted each of the primary mirror segments to produce a unified image, is what this milestone is about. The image was focused on a bright star. The star is about 2,000 light-years away from Earth.
The galaxies and stars in the background were also visible because of the sensitivity of the telescope. The foreground star is spiked in appearance because it is billions of years away. Diffraction spikes are artifacts created by a telescope's secondary mirror.
Dr. Christopher S. Baird is an assistant professor of physics at West Texas A&M University.
“Certain telescopes have a large primary mirror that focuses the incoming beam of light onto a secondary mirror or a sensor that is held over the primary mirror. The secondary mirror diverts the light out of the telescope so it can be seen or further processed. Or, alternately, a sensor held above the primary mirror converts the image to an electrical signal that is delivered to a computer.”
The primary mirror is held in place over the secondary mirror by support rods, which blocks the incoming light. As starlight enters the telescope and heads towards the primary mirror, some of it skims past the support rods. The light is shifted in the final image, forming a spider that matches the position of the support rods.
The light pattern of stars and other bright point sources is shifted by radial spikes.
One can see that the secondary mirror does not conform to a crossed or six-sided pattern. Incoming light must also pass through the edge of the telescope to cause diffraction. Diffusion rings are created by telescopes and cameras that are circular rather than spikes that are very faint.
Diffraction spikes can be caused by hexagonal-shaped apertures, which are consistent with James Webb's mirror segments.
“If the aperture is not circular but has some other shape, then both rings and spikes can result from just the aperture. Such polygonal apertures also cause diffraction spikes. Diffraction spikes seen in images taken by lens-based cameras are therefore not caused by support rods but by the non-circular aperture. In contrast, telescopes usually have circular apertures and therefore create images with diffraction spikes caused by the support rods.”
This is common with ground-based observatories. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) in China is one of the examples. The first space telescope to use such a design is the 21-foot 4-inch primary mirror of the Webb telescope.
This image is a major milestone in the process of science operations and new views of the universe. The completion of Phase 5 and the functioning of the primary imager and optical system are signaled by this. The mission team's confidence in the telescope has been boosted by the deputy optical telescope element manager, according to a recent NASA press release.
The performance of the telescope is beating specifications, she said. Over the next six weeks, the team will proceed through the remaining alignment steps before conducting the final science instrument preparations.
The team is currently in the sixth phase of preparation, where they will conduct measurements at multiple field points and extend the alignment to the rest of the instruments. The final adjustments needed to achieve a well-aligned telescope across all science instruments will be calculated in this phase.
The team will adjust any small, residual positioning errors in the mirror segments after the final alignment step. Thomas Zurbuchen is the associate administrator for NASA's Science Mission Directorate.
“More than 20 years ago, the Webb team set out to build the most powerful telescope that anyone has ever put in space and came up with an audacious optical design to meet demanding science goals. Today we can say that design is going to deliver.”
The team is on track to conclude all aspects of the OTE alignment by early May before moving on to the final two months of science instrument preparations. By this summer, the first full-resolution imagery and science data will be released. Get ready for more amazing images like this one.
The #JWSTart submissions slideshow features art inspired by the JWST.
NASA, West Texas A&M University.
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