Here's how the James Webb Telescope sees with 4 instruments at once

In parallel, Webb's instruments can reveal statistical features of the universe we've never seen before.
Brad Bergan
An depiction of Webb, in space.NASA

It's a long road to the edge of the observable universe.

From its construction, the path to the launchpad, and the journey to its orbit around Lagrange point 2 (L2), the James Webb Space Telescope is crossing every milestone on the way to its first science missions this summer.

But in March, it began to extend its telescope alignment to the guider — called the Fine Guidance Sensor (FGS) — in addition to three other scientific instruments, according to a blog post from NASA.

This process will continue for six weeks, and is called multi-instrument multi-field (MIMF) alignment. But, incredibly, it reveals a secret power of Webb: All of the instruments can be trained in the same direction, in what's called parallel science exposures.

Here's how Webb can map incredibly vast regions of deep space with four instruments, all working at once — and how that could change what we know about the ancient universe.

James Webb Telescope's instruments can point at the night sky simultaneously

Ground-based telescopes sometimes require that the instrument be physically removed from the telescope, when scientists want to swap cameras. A new one is installed in the telescope during the day, when there's nothing for the telescope to see beyond the blinding illumination of sunlight. But if the desired instrument is already installed in the telescope, internal mechanisms can move a section of the device's optics — which is called a pick-off mirror — into the correct alignment for viewing, according to a report from SciTech Daily.

But on Webb, in space, every camera can see the night sky simultaneously — pivoting from one targeted cosmic object between cameras requires scientists on Earth to simply reposition the telescope so the object is within the field of view of the desired instrument.

And, once MIMF is completed, every instrument on Webb will be fully operational, offering incredibly sharp images and great focus. Mid-March 2022, Webb's Deputy Senior Project Scientist Jonathan Gardner and Webb Deputy Project Scientist Stefanie Milam for planetary science, both at NASA's Goddard Space Flight Center, "mapped the positions of the three near-infrared instruments relative to the guider and updated their positions in the software" used to direct the telescope, according to the NASA blog post authored by the two scientists.

NASA Webb 4 Instruments
Webb's FGS guider, in addition to its four science instruments, which include NIRISS, MIRI, NIRCam, and NIRSpec. Source: NASA

Tracking the universe's behavior at colossal scales

James Webb Telescope's mid-infrared instrument (MIDI) is slated to become the final instrument undergoing alignment as it is continually chilled via cryogenic cooler to its ultimate operating temperature: less than 7 degrees above absolute zero. This will involve two stages, after which the MIMF's final stages will place the telescope in alignment for MIRI.

And, impressively, all of the James Webb Telescope's instruments can be used at the same time. During parallel science exposures, all four instruments can't observe the exact same object, since their fields of view aren't identical. But in taking "random samples" of the universe, scientists can build statistical properties of galaxies far beyond the reaches of the Milky Way's local group.

Bonus points - But for science programs mapping a colossal region of space, much of the parallel images will actually overlap, which will enhance the efficiency of the enormous datasets expected from Webb. In short, we're only a few months away from a view to the depths of the universe that goes beyond singular studies — with all four instruments activated in parallel, new data on the behavior of the universe on massive scales is going to start stacking up, fast. Among other things, this means there will be no shortage of demand for scientists to parse the datasets and help the James Webb Telescope transform and deepen our grasp of the universe's statistical behavior at unprecedented scales.

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