A personal gallery

I have been involved with the Hubble Space Telescope mission and the Space Telescope Science Institute for more than 35 years, a long time to be at one place. For most of that time I have helped translate Hubble’s amazing science data into images distributed worldwide to help describe what we have learned. It’s time for me to move on and let others participate in this effort, bringing new skills and techniques to address increasingly complex challenges.

This is a small, admittedly subjective, but representative sample from among a large number of amazing images that have come from Hubble over its many years of service (in no particular order). It started out as a top-10 list, prompted by a request from National Geographic around the time of the monumental 25th anniversary of Hubble’s launch. The original selection was published as a feature in the April 2015 issue of the magazine. Since then I’ve replaced and added a few images to the selection up to an even 16; it’s hard to remove any favorites, and Hubble continues to produce spectacular new images.

A few factors enter into this selection. First of all, it’s about the same sorts of aesthetic qualities that apply to any visual medium, photography in particular: color, composition, form, tonality, texture, etc. These images were selected more for their visual appeal than for the importance of the science they represent. There is also a technical factor: images that are sharper and clearer, with full tonal range look qualitatively better. So this selection mostly relies on images from the most recent Hubble instruments, ACS and WFC3 with improved image quality over those from earlier instruments, though the older WFPC2 produced the first really dramatic images and some of the most reproduced pictures. (Notice that one of the most recognizable Hubble images, the Eagle Nebula, is not here; that’s another story.)

But the aesthetics cannot be separated from the content, context, and meaning of the images. Understanding the nature of the subject changes the way one looks at the images, something like the difference between a recognizable, representational picture such as a landscape or a portrait, and an abstract, conceptual artwork whose meaning may be symbolic or not be immediately obvious. Understanding what we see provides another dimensional quality, analogous to decoding the meaning of seemingly abstract symbols in an ancient text.

There’s a more emotional factor to this selection as well; how much time and effort I’ve devoted to an image can’t help but affect how I feel about it. One aspect of this is that some of these were the result of new Hubble observations that were available through programs such as Hubble Heritage. I feel privileged to have been able to lead or help plan and execute Hubble observing programs dedicated to producing some of the most compelling images. Nevertheless, I never felt that they were my images since the Hubble Space Telescope observatory is a public resource funded by the people, operated by a dedicated staff and the data made available to anyone in the world.

1 – Barred Spiral Galaxy NGC 1300

The Hubble Atlas of Galaxies is a compilation of the best photographs of galaxies from the major observatories in the mid-20th century by Alan Sandage. The selection represent the various galaxy types as organized by Edwin Hubble (after whom the telescope was named). One of the most striking images in the atlas is of NGC 1300, the prototypical example of a galaxy type known as a barred spiral.

It seemed appropriate to finally get the definitive color view of this galaxy with Hubble after the ACS instrument was installed on Hubble in 2003. And the result did not disappoint. Besides the classic, dramatic form of the bold spiral structure and incongruous, straight bar, amazing details appear in the color composite: beautifully resolved spirals arms and dust lanes right to the bright nucleus, numerous star-forming regions starkly delineated in Hα, a disk transparent enough to see distant background galaxies through the galaxy, providing a dramatic feeling of depth.

2 – Carina Nebula Mosaic

The Carina Nebula Mosaic is one of the largest Hubble images (in pixel size and angular size on the sky). This image is unusual enough for its size, which results from stitching together a mosaic of 50 ACS exposures, but it’s also unusual because it combines Hubble data with images from a ground-based telescope. The image reveals one of the most dynamic, complex places we know about in our Milky Way galaxy and provides a visually striking composition, something of a mashup of abstraction and representation.

This image is a fortuitous collaboration between Hubble and ground-based observing, and a wonderful result of mining the Hubble Data Archive. The Hubble data consist of Hα exposures (recording the light of glowing hydrogen) from a large program by Nathan Smith; a mosaic covering a portion of the Carina Nebula in exquisite detail, but with no other data with which to reconstruct a color composite. The same observer also had multi-color, narrow-band images of a wider field in Carina from the CTIO 4-meter telescope, which were used to produce an exquisite color composite, albeit with lower resolution (but covering a much wider field). Combining the luminosity in the Hubble Hα with the color from the CTIO composite proved to be a technical challenge because of the wide difference in the resolution but in the end resulted in a very pleasing image with a somewhat “painterly” effect.

I have a strong emotional attachment to this image also because I spent so much time with it. A great deal of effort went into stitching together the individual mosaic tiles. In addition, there was a lot of detailed effort involved in blending the two disparate datasets.

3 – Hubble Ultra Deep Field

The Deep Field surveys will likely be Hubble’s most significant and lasting science legacy. Starting with the Hubble Deep Field in 1995 taken with WFPC2, continuing with the Hubble Ultra Deep Field in 2004 with ACS, and augmented subsequently by WFC3/IR resulting in the eXtreme Deep Field, and later iterations, these observations continue to supply a wealth of understanding about the universe as a whole, the evolution of galaxies, and lots of other fundamental information for astronomy.

Of these images, the original HDF stands out as the most significant. Newer instruments provided improvements in resolution, sensitivity, and wavelength coverage. But the original is perhaps Hubble’s most surprising and unexpected result, and the image clearly demonstrated that. The reason so much precious Hubble observing time was devoted to this one observation was that the nature and number of the earliest, most distant galaxies was not well known. It could well have been that very few galaxies would appear after days of observation. But the result was just the opposite: some 3,000 galaxies in a single tiny portion of the sky (it would require 24 million such images to cover the whole sky), many of which were farther than any galaxies recorded up to that time. The analysis of these observations has led to a much more complete understanding of the evolution of galaxies and the early universe.

Making this image also was a particular challenge because it represents the limit of Hubble’s imaging technology. The most interesting features, the faintest, most distant galaxies are barely brighter than the background noise. Yet other features are much brighter and needed to be shown clearly without losing details. It may not be the most aesthetically pleasing image, but its significance reaches far beyond what looks like a bunch of fuzzy blobs.

4 – M31 Halo

The exquisitely deep image of the outer regions of the (relatively) nearby Andromeda galaxy, the grand spiral M31, provides a spectacular example of how an image takes on greater power and meaning with understanding the subject. It may not look like much, but what we see is nothing less than the entire sweep of the cosmos in a single image. Many of the brighter objects in the scene are stars in our own galaxy, relatively nearby (hundreds to thousands of light-years away). Most of the stars in the image are actually in the Andromeda galaxy, some 2.5 million light-years away, in the extended outer regions of the galaxy, known as the halo. These stars are thousands of times more distant than most of the stars in our own Milky Way galaxy. This image nicely complements the Hubble Deep Field surveys by including relatively nearby cosmic components.

A particularly interesting feature, near the bottom of the image is a clump of stars, a globular cluster, containing hundreds of thousands of stars swarming around each other, a common feature of most galaxies, including our own. This cluster belongs to Andromeda, therefore it’s also 2.5 million light-years away. The astonishing thing about this is how clearly we see this cluster, well resolved into individual stars because of the great quality of Hubble’s images. Not too long ago, the best images we had of globular clusters in our own neighborhood looked about like this.

But there’s more … among the Andromeda Galaxy stars we see other objects, a bit fuzzy and extended, but with noticeable structure. These are other galaxies, not too different from our own and Andromeda, that are even farther away, maybe a thousand times as far as Andromeda, millions to billions of light-years away.

5 – V838 Mon Light Echo

This is an image of a phenomenon as much as an object, albeit an object with spectacular form and texture. This is one of a series of “snapshots” of the ongoing phenomenon that took place over many months showing the light from a star’s outburst traveling through the surrounding space, illuminating material ejected by the star at a much earlier epoch. It provides a very unusual opportunity to follow a rapidly changing subject and the rare ability to tease out the full 3D structure of such an object.

6 – Interacting Galaxies Arp 273

Galaxies collide! The titanic gravitational forces rip apart entire galaxies consisting of hundreds of billions of stars, eventually forming completely different structures over time scales of millions to billions of years. Interacting galaxies provide some of the most interesting and varied visual forms known in space. Arp 273 is perhaps the best example from the many examples from Hubble.

7 – Planetary Nebula NGC 5189

The Hubble Space Telescope has provided views of planetary nebulae with unprecedented detail, showing that they are wildly varied in their shapes and leading to a much better understanding of their formation and dynamics. NGC 5189 is a fine example of this with an amazing spiral, point-symmetric form and unusual color. As with most Hubble images, it’s the best available view of this subject.

8 – Tarantula Nebula (30 Doradus)

As one of the largest known regions of star formation anywhere, the Tarantula Nebula has been studied in great detail for quite a while with every available observatory. Hubble provides the opportunity to get images of this dramatic region in the Large Magellanic Cloud with detail comparable to similar places in our own galaxy even though it’s much farther away. This image was made with WFC3, not long after the instrument was installed during the last Hubble servicing mission in 2009, and represents the best image of this region up to that time, showing the brilliant cluster of bright, hot, young stars blowing a cavity in the cloud from which they formed, and from which new stars are still forming.

9 – Pillars and Stellar Jets in the Carina Nebula (Mystic Mountain)

These pillars show the telltale signature of new stars forming at their tips, strong jets of material being ejected into the interstellar medium for great distances. Many such features exist in the Carina Nebula, a vast area of dust and gas in our Milky Way galaxy. This is the most obvious and spectacular feature among many similar ones in one portion of the immense mosaic of Hubble images made a few years before. Using the mosaic based on relatively minimal Hubble data as a map, this region was imaged more completely, providing a view in full color revealing an amazing landscape never before studied in such detail. The processes at work here are very similar to what’s going on in many other such regions of the Milky Way, most famously in the familiar “Pillars of Creation” in the Eagle Nebula.

10 – Sombrero Galaxy M104

This image has a large emotional connection for me, and fulfills something of a long-time dream, besides being a compelling image of a very recognizable and popular target for astronomers and astrophotographers. This is a spiral galaxy seen nearly edge on; the dark band across the center is the result of material in the flat disk of the galaxy obscuring light of stars and gas behind it. The glowing bulge represents a population of stars largely different from those inhabiting the flat disk. If we look in detail we can see numerous globular clusters that appear as slightly fuzzy stars, like a loose swarm of bees buzzing around the galaxy, each of which is itself composed of many hundreds of thousands of stars.

A strong emotional component of this image for me is that this galaxy was the subject of intense study by one of my undergraduate astronomy professors. It was particularly gratifying to be able to produce an image from the Hubble Space Telescope of this target that he had worked with decades ago using some of the greatest telescopes of that era. I also recall him describing the awe of seeing this and other objects visually with these same telescopes, not possible with Hubble, of course. We have lost some of the romance of astronomy with remote observing. The trade-off of course is operating more sophisticated instruments without subjecting humans to the extreme conditions at the top of mountains or in space.

11 – Infrared Horsehead Nebula

It can be a challenge to get a different view of an iconic subject, as most photographers can relate to when shooting in popular locations like national parks. The Horsehead Nebula is one of the most recognizable deep sky subjects, something like Old Faithful geyser in Yellowstone National Park. It is a dense cloud of gas and dust, embedded in a much larger structure, and obscuring the light from the surrounding glowing gas. It is a favorite target of astrophotographers because of its unusual and recognizable shape.

With a camera that records near-infrared light, Hubble was able to get a very different view of the Horsehead. In infrared light, the Horsehead takes on a whole new appearance because the dust in the region blocks most visible light but is transparent to infrared light. This Hubble view is not unprecedented, but is the most detailed view in the infrared to date, and is a preview of what will be coming from the James Webb Space Telescope.

12 – Saturn and Its Moons

Saturn may be the most visually pleasing of the planets in our solar system not only because of the spectacular ring/disk system, but also because of the subtle, banded cloud structure in the atmosphere and the dance of the moons and shadows. While Hubble’s view is not as close-up as the Voyager or Cassini spacecraft, it does allow the amazing system to be seen as a whole. In addition, Hubble provides the opportunity to monitor the entire system consistently over a long time span. There’s also a nice video showing some of the moons and their shadows sliding across Saturn’s face.

13 – Veil Nebula (Cygnus Loop)

The Cygnus Loop is the monumental result of a supernova explosion, a massive star that blew itself apart. The remnants glow as they plow through other material in interstellar space. Hubble has made several images of this vast landscape, but only very small sections at a time. Nevertheless, the great resolution permits a very detailed look at those small patches, revealing extraordinary technicolor filaments.

14 – 2MASX J00482185-2507365, NGC 253

This image has always intrigued me as a study in layers. What we see mostly is a beautiful spiral galaxy, and then we notice another smaller but similar galaxy superimposed on the larger one, clearly in front because the light from the larger galaxy is darkened by dust in the smaller galaxy’s disk. We also notice a scattering of stars over the whole image. These stars are in the outer “halo” of a much larger galaxy mostly out of the frame. The larger view shows an increase in the density of stars toward the right in the image, which more clearly shows the brightening disk of the larger galaxy. Beyond this dance of galaxies we also see much more distant galaxies, and in the larger image we see stars in our own galaxy, very close to us relative to the stars in NGC 253.

15 – SNR 0509-67.5

This is a remarkable, almost ghostly image, a nearly perfect ring hanging against a starry sky. Actually it’s a bubble of gas, the remnants of a star torn apart in a supernova explosion 400 years earlier, expanding out into interstellar space known as Supernova Remnant 0509-67.5 (the designation derives from its position in the sky). The bubble is immensely large and far away, in our nearest neighboring galaxy, the Large Magellan Cloud. The simplicity of this image is haunting but deceptive. We see it as a ring, though it’s the nearly equally thick surface of a sphere. The bubble is not perfect; it’s distorted by material in the space between the stars, even though that material is incredibly tenuous. If we could get closer or get even more detailed images, we would probably find the same sort of exquisitely detailed structures as in the Veil Nebula image (see #13 above).

The image is a composite of a few different observations. The bubble was imaged as part of a science program in a single filter recording the light of hydrogen. Later, another set of observations obtained images in several filters to produce an image that showed realistic colors of the stars in the field.

16 – Abell 370

This is an extremely profound, if visually abstract image. It’s a very deep exposure of an extremely distant cluster of galaxies. But among the menagerie of fairly familiar shapes of spiral and elliptical galaxies along with a couple of much closer stars, there are some oddly distorted, unusual shapes. These are optically distorted galaxies, much farther than the cluster. The mass in the cluster, some associated with the visible galaxies, but a lot of it not – known as dark matter – is causing the light from the more distant sources to be bent, focused, and magnified. This “gravitational lensing” was first described by Albert Einstein as a consequence of his groundbreaking ideas about gravity. This and other lensing clusters are a beautiful confirmation of his theories. But there’s even more: because of the potential magnification of the light, we can record objects much farther away than we could if the cluster were not there. So this galaxy cluster, and many more like it, act as a natural telescope to extend our view of the extremely distant universe.

The name, Abell 370, has an interesting history, as does most astronomical nomenclature. Abell refers to the late astronomer George O. Abell, who compiled the first comprehensive catalog of galaxy clusters in the mid-20th century from a monumental photographic survey of the northern sky made with the then-new 48-inch Schmidt telescope at the Palomar Observatory. This is one of over 4,000 clusters in Abell’s catalog.

George Abell is also well known as the author of a popular introductory college astronomy textbook, Exploration of the Universe, which I used in my first astronomy course in 1970. It’s often said that the Hubble Space Telescope has rewritten the astronomy textbooks. As I page through my old copy of Abell (second edition), much of it is still valid of course, as it’s fundamental astronomy well understood for a long time. But it also becomes clear that the Hubble Space Telescope has vastly extended our view and our understanding of the universe, far beyond what was known just a few decades ago.

It is very rewarding to look back over a few decades and the entire history of the world-changing Hubble Space Telescope mission. The decision to leave such a world-class institution is not easy. The images I’ve selected here, along with many more, represent the monumental achievements of a lot of people in many disparate walks of life who conceived, designed and built the telescope, maintain it and keep it operating at peak performance, archive the data and make it available worldwide, analyze the science, and publicize the results. Thanks to everyone who makes this possible.