Sky Library / Behind the pictures

How to read Webb’s first deep field

Webb combined infrared measurements into a color image. The colors label measured bands rather than ordinary human vision. Each filter records a chosen infrared range. Scientists assign visible colors so readers can compare those ranges. The image collects faint light over many hours. The source record lists the filters, instrument and observing date. A single color can represent more than one measured band. Background galaxies appear distorted because the foreground cluster bends their light. The effect is gravitational lensing. Diffraction spikes come from Webb’s telescope optics. It does not show a single instant through human eyes.

Infrared measurements become assigned colors

Webb observed SMACS 0723 with NIRCam on 7 June 2022. NASA released the composite on 11 July 2022. The image combines 12.5 hours of observations.

NASA assigns F444W to red and F356W to orange. F200W and F277W appear green. F090W and F150W appear blue.

Those colors do not turn infrared light into an ordinary visible-light view. They help compare measurements from separate filters. The source record explains the bands and the observation.

Curved galaxies near the cluster result from gravitational lensing. The cluster’s gravity bends light from galaxies behind it. Bright foreground-star spikes come from telescope optics.

SMACS 0723 is the foreground galaxy cluster in this view. Its gravity magnifies and distorts galaxies farther behind it. Those arcs help reveal objects that would otherwise appear fainter.

The image covers a tiny patch of sky. Its many galaxies appear because Webb collected faint infrared light over time. A bright point can be a foreground star or a distant galaxy. Use the record captions before naming a feature.

This guide links to the source record. It does not host or display the Webb file. The exact source credit is NASA, ESA, CSA, STScI.

Sources and image credits

Written for beginners from the sources above. How we research and correct the library. Found an error? Tell us.