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35 years ago, NASA launched its first great observatory: the Hubble Space Telescope.
This photo shows the Hubble Space telescope being deployed, on April 25, 1990, one day after its launch. It was taken by the IMAX Cargo Bay Camera (ICBC) mounted aboard the space shuttle Discovery. It has been operational for 35 years, and has not been serviced since 2009. With a 2.4-meter diameter mirror, it gathers as much light in 1 minute as a 160-mm (6.3″) telescope would require 3 hours and 45 minutes to gather.
Credit: NASA/Smithsonian Institution/Lockheed Corporation
When it achieved first light, a huge problem appeared: its optics were flawed.
This 1990 image was the “first light” image of the then-brand-new Hubble Space Telescope. Owing to the lack of atmospheric interference along with Hubble’s large aperture, it was able to resolve multiple components to a star system that a ground-based telescope could not resolve. When it comes to resolution, the number of wavelengths of light that fit across your primary mirror’s diameter is the most important factor, but this assumes the mirror is ideally, perfectly shaped, which was not the case for Hubble initially.
Credit: E. Persson (Las Campanas Observatory, Chile)/Observatories of the Carnegie Institution of Washington; Right: NASA, ESA and STScI
This spherical aberration flaw kept Hubble images from achieving their designed sharpness.
This three-panel image shows the same targeted region with a ground-based telescope that achieves 0.6″ resolution (left), Hubble’s WFPC1, pre-COSTAR image of that same field of view (center), highlighting the spherical aberration problem of the mirror, and the post-servicing mission view of the same star field with Hubble (right), with COSTAR and WFPC2 installed. The difference in resolution and the types of features that can be resolved is breathtaking.
To correct this, a servicing mission was flown in December of 1993.
One huge upgrade was COSTAR’s installation: a corrective optics package.
NASA astronauts Kathryn Thornton (top) and Thomas Akers (bottom) prepare the Corrective Optics Space Telescope Axial Replacement (COSTAR) package for installation aboard the Hubble Space Telescope on the STS-61 mission in December of 1993. Thornton can be seen anchored to a foot restraint on the end of the Remote Manipulator System arm.
A second was WFPC2: an upgraded, wide-field camera for superior imaging.
Astronaut Jeffrey Hoffman removes Wide Field and Planetary Camera 1 (WFPC 1) during change-out operations, where it was replaced with the upgraded WFPC2, during the first Hubble servicing mission. Along with the installation of COSTAR, the astronauts of STS-61 in December of 1993 significantly upgraded the Hubble Space Telescope, transforming it into the powerhouse observatory it’s become renowned for over its 35+ year lifetime.
Credit: NASA
Once installed and calibrated, Hubble’s improvement in image quality was magnificent.
This side-by-side image shows the same object: galaxy Messier 100, as imaged with the Hubble Space Telescope before (left) and after (right) 1993’s first servicing mission. The left picture was taken on November 27, 1993, while the right picture was taken on December 31, 1993: after the installation of COSTAR and WFPC2.
Some photographs, like the original Pillars of Creation, swiftly became iconic.
The original Hubble view of the Pillars of Creation in the Eagle Nebula, although first released in 1995, are still spectacular and iconic today, with these dusty regions serving as a location of star-formation: one of the last ones remaining within the nebula.
Then in late 1995, STScI director Robert Williams made a bold, largely unpopular decision.
Shown here lecturing and taking a question from the audience in 2025, celebrating the 30th anniversary of the original Hubble Deep Field, former STScI director Bob Williams was the one who believed in the scientific value of deeply imaging a blank patch of sky with a flagship-class telescope for the first time. His detractors feared that so much observing time would be devoted to literally imaging nothing, revealing no objects of astronomical value at all. Williams’ decision led, arguably, to the most impactful space telescope image of all-time.
He devoted his director’s discretionary time to imaging nothing, very deeply, for studying distant galaxies.
The blank region of sky, shown in the yellow L-shaped box, was the region chosen to be the observing location of the original Hubble Deep Field image. With no known stars or galaxies within it, in a region devoid of gas, dust, or known matter of any type, this was the ideal location to stare into the abyss of the empty Universe. Today, we know of even more pristine, empty regions of space than we did in the early 1990s.
A total of 342 Hubble exposures across four separate wavelengths were acquired.
This four-panel image shows, clockwise from top left, the same small region of the Hubble Deep Field as imaged at wavelengths of 300 nanometers, 450 nanometers, 606 nanometers, and 814 nanometers: from ultraviolet through the visible and into the infrared.
The result was unprecedented: the first Hubble Deep Field.
The original Hubble Deep Field image, for the first time, revealed some of the faintest, most distant galaxies ever seen. Only with a multiwavelength, long-exposure view of the ultra-distant Universe could we hope to reveal these never-before-seen objects.
Over 3000 galaxies were exposed.
With appropriate measurements taken in a variety of wavelength filters, distances and lookback times can be inferred for each galaxy imaged in a deep field view of the Universe. Galaxies can be sorted into nearby, intermediate-distance, and great distance bins in the Universe. The earliest galaxies found in the deepest images of the Universe take us back to merely a few hundred million years after the Big Bang.
These discoveries set up future, superior deep fields.
The Hubble eXtreme Deep Field (XDF) may have observed a region of sky just 1/32,000,000th of the total, but was able to uncover a whopping 5,500 galaxies within it: an estimated 10% of the total number of galaxies actually contained in this pencil-beam-style slice. The remaining 90%+ of galaxies are either too faint or too red or too obscured for Hubble to reveal, but when we extrapolate over the entire observable Universe, we expect to obtain a total of upward of 2 trillion galaxies: up to 6-20 trillion, at present.
More efficient cameras, longer exposure times, and greater wavelength sensitivities better reveal the ultra-distant Universe.
Looking back through cosmic time in the Hubble Ultra Deep Field, ALMA traced the presence of carbon monoxide gas. This enabled astronomers to create a 3-D image of the star-forming potential of the cosmos. Gas-rich galaxies (imaged by ALMA) are shown in orange, whereas Hubble’s details are shown in violet. You can clearly see, based on this image, how ALMA can spot features in galaxies that Hubble cannot, and how galaxies that may be entirely invisible to Hubble could be seen by ALMA.
Today’s farthest-flung galaxies are found exclusively in these regions of deep-field imaging.
JADES-GS-z14-0, in the top inset box, is found behind (and just to the right of) a closer, brighter, bluer galaxy. It was only through the power of JWST spectroscopy with incredible resolution, capable of separating the two sources, that the nature of this record-breakingly distant object could be determined. Its light comes to us from when the Universe was only 285-290 million years old: just 2.1% of its current age. JADES-GS-z14-1, just below it, comes from when the Universe was ~300 million years old. Compared to large, modern-day galaxies, all early galaxies contain a paucity of stars and have irregular, ill-defined shapes.
We dare to explore the unknown in novel ways.
The JADES observing areas, undertaken by JWST, include a total area of the sky of 125 square arc-minutes, and include both the Hubble Ultra/eXtreme Deep Fields (left) and the original Hubble Ultra Deep Field image (right). Of the most distant objects of all in this region, 93% were uniquely observed by JWST; only 7% of them were also seen by Hubble. All told, JADES will spend 770 hours observing their target region with NIRCam and NIRSpec. This image, from JADES data release 1, will be updated to include new data in light of the latest data release.
That’s how fundamental human knowledge continues to advance.
This section of one of our deepest views of the Universe, acquired with JWST, overlaps with data from the Hubble eXtreme Deep Field. Compared to Hubble, JWST reveals an enormous number of objects previously invisible to Hubble, even with only ~4% of the observing time. Most of these galaxies are small and low-mass, but are forming stars rapidly right now, enabling JWST to reveal their presence.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.
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Travel the universe with Dr. Ethan Siegel as he answers the biggest questions of all
