JWST is now fully focused

The telescope is now focused.

!!

The L2 point is 1.5 million kilometers from the Earth in a direction opposite the Sun. The sun shield and mirror array were deployed while it was on its way. After that, the 18 hexagonal mirror segments began a long phase of adjusting their positions to align them with the stars.

The phase was completed in March of 2022. It wasn't done yet. The testing up that point was done using the Near-Infrared Camera, one of several scientific instruments on board. It is the workhorse camera and the one in the future from which you will see most of the pictures.

Each of the observatory's scientific instruments has its own requirements. It was time to get things working for the other three after the NIRCAM tests showed that all the mirrors were focused.

All of them are focused now. The optical performance of the telescope continues to be better than the engineering team's most optimistic predictions.

To maximize their ability to get stars in each instrument, engineers pointed JWST to the Large Magellanic Cloud. Thousands will be seen by each detector, because it has billions of stars and 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 888-349-8884 As you can see.

NIRCAM is sensitive to light that is between 0.6 and 5 microns. The short end of the light is what our eyes see as red. Everything past that is visible. Everything will be looked at by NIRCAM. NIRCAM can take a look at anything an astronomer wants to see.

There are two detectors that look at a spot in the sky. The field of view is 2.2 arcs per second on a side, and for comparison the full Moon is about 30 arcs per second. The smallest thing the human eye can see is about a tenth of a second. NIRCAM's size will allow it to get high-resolution images.

The MIRI can detect much longer wavelength from 5 to 28 microns. It's more sensitive to objects that emit at those wavelength, including brown dwarfs, dust around other stars and cold Trans-Neptunian objects.

In the focused image you can see stars in the LMC as well as gas and dust around them, the galaxy is lousy with the building blocks of stars and is very busily making them. Astronomers will be able to understand how stars form from this material with the detail in these images.

The FGS is an engineering instrument that is designed to lock on to guide stars and keep the telescope pointed with incredible accuracy. These test shots show that it can be used to make images. The LMC is loaded with clusters and this gives a nice indication of the high quality resolution these cameras afford.

The Near-Infrared Imager and Slitless Spectrograph is also in the same assembly as the FGS. It can take images, but its main function is to break up the incoming light into individual wavelengths, so that it can be used to measure a lot of things. NIRISS and NIRSPEC are designed to maximize this potential, even though all the instruments on JWST can do this to one degree or another.

When will we see science images and data? Not for two more months! Why wait? These machines cost hundreds of millions of dollars to design, build, and test, and each mode has to be individually tested. The process needs to be done carefully.

In 1997 I was part of a large team that worked on the commission of the Space Telescope Imaging Spectrograph (STIS), which was installed on Hubble. It took weeks, months, because each one of the different ways to look at the sky had to be tested. I was in the middle of all that, comparing on-orbit observations with data we had collected for years testing it on the ground, making sure nothing was awry and that we understood what our camera was doing.

That was only one instrument, and the other five were from the same company. Getting everything ship-shape and tightened up in two months will be a miracle. A lot of engineers and scientists will be working very long hours for those two months, sweating out details to make sure these incredibly sensitive machines work at their optimum abilities.

We will all get the benefits come July or so.