OK it is really late here, but today's reveal of the first JWST image of the galaxy cluster SMACS-0723 was amazing, and I am still digesting it. There is so much stuff going on, it is absolutely breathtaking!

Just to get an idea of what an improvement this is over Hubble, over at The Robot Report, they show this beautiful side-by-side view of the previous best image taken with Hubble, and tonight's result. It's wild.


So, I guess the left is a Hubble visible spectrum image, whereas the JWST image is infrared, mapped to RGB color bands for display.

Reading about this, it looks like NIR only images 2-bands, roughly centered at 2μm & 4μm, not three, so they've remapped the colors in some way to generate the 3-band color image we see.

Not sure exactly how they do that, but I'd naively assume something like red = B, green=(A+B)/2, blue=A, where A is the 2μm band and B is the 4μm.

@TerryHancock My guess is that the HST imaging is mainly in infrared - Hubble's sharpness in UV and Optical is comparable to JWSTs in the near-infrared. But Hubble's sharpness is quite dramatically worse in the IR, as is also clearly visible here.


@TerryHancock No, RELICS is much newer, the IR images are taken with the WFC3/IR channel, in the filters F105W, F125W, F140W, and F160W. My guess is the image is some combination of (some of ) those.

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@TerryHancock ...You can find the HST image of the cluster on the RELICS website and it does indeed look like it is the ACS-WFC3/IR image on the upper left that is shown in the comparison.

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