Oh My Heavens!

Rex Saffer the AstroDoc
7 min readJul 13, 2022


1 The heavens declare the glory of God;
the skies proclaim the work of his hands.
2 Day after day they pour forth speech;
night after night they reveal knowledge.
3 They have no speech, they use no words;
no sound is heard from them.
4 Yet their voice goes out into all the earth,
their words to the ends of the world.
In the heavens God has pitched a tent for the sun.
Psalm 19:1–4, New International Version

On July 11–12, NASA released the first full–color scientific images from the James Webb Space Telescope (JWST). This is a long–awaited waypoint along a contemporary Space Odyssey that began with JWST’s launch on Christmas Day, 2021 (what a great gift from Santa!!), followed by a dramatic 6–month long series of deployment and calibration operations to bring the world’s largest and most capable space observatory to full operational status. You can explore the full launch, deployment, orbital insertion, and instrument commissioning sequences here. Use the thumbnail icons or the grey scroll bar below the icons to select any of the dozens of mind–boggling technical and scientific accomplishments leading up to this week’s spectacular data release.

The images just released were produced by JWST’s suite of instruments, which are capable of 17 different modes of operation:

NIRCam (Near–Infrared Camera)
· Imaging
· Wide field slitless spectroscopy
· Coronography
· Imaging time series
· Grism (diffraction grating/prism) time series

NIRSpec (Near–Infrared Spectograph)
· Multi–object spectroscopy
· Fixed slit spectroscopy
· Integral field unit spectroscopy
· Bright object time series

NIRISS (Near–Infrared Imager and Slitless Spectrograph)
· Single object slitless spectroscopy
· Wide field slitless spectroscopy
· Aperture masking interferometry
· Parallel imaging

MIRI (Mid-Infrared Instrument)
· Imaging
· Low resolution spectroscopy
· Medium resolution spectroscopy
· Coronographic Imaging

In addition, the FGS (Fine Guidance Sensor), which controls the fine pointing of JWST, can be used as an imaging instrument.

We will concentrate here on the very first image release of July 11, a wide–field view called the “JWST Deep Field”. You can find a full size, high resolution image here. It will be useful to say a few words on this topic before delving into the many fascinating aspects of the image, because this is not the first Deep Field.

The Hubble Space Telescope launched on April 24, 1990. Immediately upon opening its aperture cover and obtaining its first images, the telescope mirror was found to be flawed, having been exquisitely and precisely polished, in effect, to the wrong optical prescription. This kind of engineering debacle is called a “cascade failure”, where an error in one part of a system can trigger a series of subsequent errors. The system can survive any one of these errors in isolation, but taken together they lead to an overall system fiasco. The telescope was restored to design specifications by the first HST Servicing Mission in December 1993, carried out aboard STS–61, the fifth flight of the Space Shuttle Endeavour.

Two years later, Dr. Bob Williams, at that time Director of the Space Telescope Science Institute (STScI), used his own Director’s Discretionary telescope time to point HST at an apparently blank area of deep space, where it obtained a continuous series of 342 separate exposures with the Wide Field and Planetary Camera 2 (WFPC2) for ten consecutive days between December 18–28, 1995. This was a controversial use of the telescope, and there was some opposition to it on the grounds that the resulting images, unlike all other carefully planned HST science observations, might well be a colossal waste of time and effort. How wrong those objections were! Incidentally, I was a Hubble Postdoctoral Fellow at the Institute when all this happened. It was one of the most exciting times in all of my professional career.

The HST IR Deep Field (HDF) is at left, the JWST IR Deep Field (JDF) at right, both displayed at the same spatial scale, with a width of about 2.3 minutes of arc. This is equivalent to the apparent width of a dime viewed from a distance of 75 feet. There are two comparisons to be made: 1) While it is not immediately apparent from the resized images above, there are many more faint galaxies visible in the JDF, because JWST is capable of detecting light as much as 100 times fainter than HST, and 2) The JDF images are significantly sharper, that is, with higher resolution than the HDF. As Dr. Williams remarked,

The variety of galaxies we see is amazing. In time these Hubble data could turn out to be the double helix of galaxy formation. We are clearly seeing some of the galaxies as they were more than ten billion years ago, in the process of formation. As the images have come up on our screens, we have not been able to keep from wondering if we might somehow be seeing our own origins in all of this. The past ten days have been an unbelievable experience.

The JDF is sure to be all of that, and so much more. And this is just from one of JWST’s suite of instruments! Now, let us discuss some of the features of the HDF and JDF, beginning with the imaging of faint, extended objects. Both images below are shown at the same spatial scale.

Closeups of HDF (left) and JDF (right)

The brightest point–like objects in each field are foreground stars within our own Milky Way galaxy. The spikes radiating from them are just that, “diffraction spikes” caused by interference of the incoming light with the structure supporting each telescope’s secondary mirror. This produces the four spikes seen at left in the HDF. In the JDF at right, these are augmented by a second, six–pointed pattern due to the hexagonal shape of JWST’s individual primary mirror segments. Every other object in each field is a distant (very distant!) galaxy, even the faintest specks of light visible in the JDF. The superiority of JWST’s ability to image galaxies much fainter than HST, as well as the vastly better resolution, is obvious.

Another feature in the JDF missing from the HDF is the collection of smeared circular arc segments in the JDF’s central area. This is due to a phenomenon called “gravitational lensing”. It is caused by the gravitational influence of the massive cluster of galaxies filling much of the JDF upon more distant, background galaxies.

Gravitationally lensed arcs, arrowed

Let’s take a little side trip into this topic. Einstein’s general theory of relativity describes how mass concentrations distort the surrounding spacetime continuum. A gravitational lens can occur when a huge amount of matter, like a cluster of galaxies, creates a gravitational field that distorts and magnifies the light from distant galaxies that are behind it. Light from the background objects propagating along different paths away from the direct line of sight to the Earth are redirected toward it and appear as multiple short, thin lensed arcs around the outskirts of the cluster.

Gravitational lensing of a distant galaxy by an intervening massive galaxy cluster

These lensed images can be used as probes of the matter in the galaxy cluster. Complex theoretical modeling of the size, shape, and intensity of the lensed arcs can be used to reconstruct the amount and distribution of all the matter in the cluster, which in general is not uniform but lumpy and asymmetrically distributed.

Such analyses reveal that most of the matter in a galaxy cluster is not in the galaxies themselves or the hot gas around them, which emit the visible radiation detected in telescopic observations. To explain the arcs, there must be a significantly more prevalent form of matter that, while like all other matter does strongly affect the overall shape and dynamics of the galaxy cluster through its gravitation, does not emit light.

Considering the whimsical personalities of many scientists, this has been unimaginatively named “dark matter”, and our best observations today indicate that of all the matter present in the universe, there is 6 times as much dark matter as visible matter. The identity and nature of dark matter is not known, but there are several exotic subatomic particles hypothesized in advanced quantum mechanical models of the Universe. None have yet been detected, although a few experiments have been proposed to do so. Stay tuned for more bulletins as events warrant.

We are just getting started. The precision with which JWST was inserted into its HALO Orbit around L2, the Lagrange point 1.5 million kilometers from Earth directly away from the Sun, used so little of its maneuvering fuel that the telescope will be able to maintain its position for much longer than was originally anticipated, from its original design lifetime of some five years to more than ten years. And we haven’t even begun to discuss the images from the rest of the science instruments, nor is there time or space to do so here. You can find much more at JWST’s Recent News site.

All the best,
From Broomall, PA on Wednesday, July 13 at 11:45 AM,



Rex Saffer the AstroDoc

Retired Physics Professor, Motorcyclist, Bridge Player, Voracious Reader, Philosopher, Essayist, Science/Culture Utility Infielder