Comets, asteroids, … and writers

 kw: book reviews, nonfiction, memoirs, astronomy, comets, asteroids, astronomers, poetry

My introduction to the Internet was when my company made it available to our desktop computers in June, 1994. Just a month later I was able to see the wonderful telescopic pictures of Jupiter, bruised and battered by Comet Shoemaker-Levy. At night, I would get out my 3-inch diameter telescope and look at Jupiter. I could just see the black spots of the impacts at 120x, which is about the limit with such a small telescope. The planet appeared about the size of a pea.

In preparation for an online lecture by David H. Levy, co-discoverer of the comet, a friend in a local astronomy club gave me a copy of Levy's recent book Star Gazers: Finding Joy in the Night Sky. It is a lovely little book; I finished reading it in two days. I could have finished even faster, but Dr. Levy's writing rewards close reading.

I find that he has discovered or co-discovered 23 comets and hundreds of asteroids. Once in a while a comet gets bright enough for any of us to see, and then star parties like this one multiply (Image generated by GPT-Image 2.5 via Leonardo AI).

In this memoir he also reports witnessing about 200 eclipses, mostly lunar eclipses, but including at least ten solar eclipses. In Chapter 4 he includes the discovery photos of Comet Shoemaker-Levy. Most comets are discovered photographically, by taking a photo of a likely spot (generally along the ecliptic, the Sun's apparent path in the sky), and then another one of the same spot an hour or two later. Looking at the images as a stereo pair, you can see something that moved as an object that seems to hover above the apparent plane of view. This also works for finding an asteroid, which appears as a "hovering" star, while a comet image is more like a smudge or tiny cloud. Right up until today, human binocular vision is superior to any technological imaging method. It is why asteroid hunting with wide-frame cameras is being carried out by citizen science to verify tentative machine identifications.

The book is composed of small essays, just one or two or three pages each, that the author has published elsewhere, with added introductions to most chapters. They are arranged by topic, not chronologically. The book ends with an ode to his late wife Wendee.

I wish to comment on writing itself. Dr. Levy writes lyrically without any loss to scientific merit. He calls himself an amateur astronomer, as do the references to him I have found. He is perhaps the poster child for amateur science, understanding that "amateur" derives from a Latin word for "lover". He has his own observatory with a few telescopes in it, named Jarnac Observatory. Many of his discoveries were made there, but numerous others were made in the company of friends, including Gene and Carolyn Shoemaker, co-discoverers with him of the "hammer that hit Jupiter." 

His doctoral dissertation dwelt on references to astronomy and astronomical objects in the writings of Shakespeare, and he has written of other literary lights who loved astronomy. He tells of reciting or reading poetry at most meetings of astronomical societies he attends. Many great scientists have also been lovers of the arts, from Leonardo DaVinci, of course, to Albert Einstein, who played violin to relax, and a great many others. Having an artistic mind seems to lend itself to having a scientific outlook.

For this reason I prefer STEAM to STEM: Science, Tech, Engineering, Arts, and Math. They all wrap up together and buttress one another in a wonderful synergy.

I intend to track down other books he has published, and I look forward in just a couple more days to attending his online lecture.

The first Mars generation

 kw: book reviews, nonfiction, science, astronomy, astronomers, biographies, mars, social phenomena

In 1877, Mars and Earth had a "great opposition". The two planets were close together, just about 56 million km (35 million miles). The orbit of Mars is somewhat elliptical, so at "less favorable" oppositions, dates when Mars is directly outward from the Sun and high in our night sky at midnight, the distance can be as great as 102 million km (63 million miles). Astronomer Giovanni Schiaparelli took advantage of the great opposition to observe Mars nightly, for weeks. In addition to blotches and pale areas, he saw a few seemingly linear features, which he called canali, the Italian word meaning "channels".

The word canali does not refer to artificial waterways; other meanings are "troughs" and "gullies". Unfortunately for the next generation or two of the American and European public, when Schiaparelli's  work was translated into English, the translator chose to use the word "canals".

About seventeen years later, Percival Lowell, nearing the age of forty, having observed Mars in telescopes located in Boston and elsewhere, built his observatory near Flagstaff, on "Mars Hill". With the 24-inch diameter telescope he installed there, he watched Mars obsessively during every period of opposition. The drier, steadier air in Flagstaff enabled him to see the planet more clearly. Over time, he discerned numerous linear features, writing of them as "canals". He inferred that they were produced by intelligent Martians.

Lowell's articles, books, lectures, drawings and later photographs of Mars stirred a kind of Mars Mania for a generation, as described by David Baron in The Martians: The True Story of an Alien Craze that Captured Turn-of-the-Century America.

Percival Lowell was rich, driven, obsessive, and probably bipolar. He had earlier had a varied career, including being a kind of envoy for Korea and Japan. Once the observatory was completed, and he had released his book Mars, the planet and his theories about the Martians and their engineering abilities dominated his life and enthralled the public.

His public lectures and writings kept Mars Mania going for the rest of his life, in spite of opposition from roughly half of the scientific establishment. One particularly telling blow came from an experiment conducted by Walter Maunder, which became known as the "Small Boy Theory". Maunder began with maps of Mars produced by Schiaparelli and Lowell. He removed all the canals and replaced them by scattered dots or bits of riverine shapes. For each of several tests, such a doctored map was hung high on the wall at one end of a large classroom, and schoolboys were seated throughout the room. They were asked to copy the map as well as they could, without moving from their seats. Those closest to the front made the best facsimiles, of course. The farther back a boy sat, the more likely he was to add straight lines where dots and fragments seemed to run together in his vision.

Lowell never wavered from his view of a canal-riddled Mars. This image from page 62 shows one of his maps showing the "canals" and "oases" (dots) he drew. Just below it is an image I captured from Google Mars, taking in the approximately same view of the planet. The straight edges of some dark areas are artifacts of different camera views stitched together.

The scattered dots in the lower image are craters. I remember in 1965 when the Mariner 4 spacecraft sent us images of Mars that resembled a moonscape: loads of craters, and no canals. This was just a century after the Flagstaff Observatory was established.

Have you looked at clouds to see "cloud animals" and other fantasies? Various amorphous shapes can look like faces. There is a blotch in the abstract pattern in my shower that looks a little like a panther's head, only when I have my glasses off. This is called pareidolia. A roughly lined-up string of spots can look like a straight line when seen from a certain distance.

But what further affected Lowell as he aged was a bad case of confirmation bias. It's something we are all prone to: when we like an idea, we remember facts that support our view and discount those that don't.

At one point, Lowell spent some time looking at Venus. He produced the map in the upper part of this pair (from page 76). He was told that the "map" seemed to just reflect the blood vessels in his retina; he apparently agreed, and retracted the map. 

I've viewed Venus a number of times with various size telescopes. To a normal human eye, it is featureless, a blank white disk. However, if Lowell had lived a century later, and had a cataract operation, he might have seen features on the surface that are visible in ultraviolet light, particularly if he used a dark blue filter such as Cobalt glass. The lower image simulates such a view; I just "blued up" an ultraviolet photo of Venus. The natural lenses in our eyes are yellow, to filter out deep blue and UV light, which are hard to focus and tend to blur the vision. Cataract operation patients can see more UV than the rest of us.

Well, that would only be true before 1980. Since then, the plastic lenses that are inserted to replace the natural lens also filter out UV light. Oh, well, my hopes of getting my cataracts out and gaining UV vision are dashed!

Percival Lowell married at age 53. Eight years later, somewhat a fallen hero but still well remembered by the public that had been enthralled by his lectures, he passed away at age 61. When Clyde Tombaugh discovered Pluto in 1930 Lowell was still sufficiently famous that the planet was given the symbol ♇ using Lowell's initials.

I have just skimmed over Lowell's life. I sympathize with his "neurasthenia", which was probably depression in the "low" phase of bipolar syndrome. I've been there. David Baron did an amazing amount of research to put this book together. The apparatus—source notes, bibliography, list of illustrations, and index—take up a quarter of the volume, almost 80 pages. Many other people who surrounded Lowell and the Mars phenomenon, including Nikola Tesla, Sir Arthur Conan Doyle, and Camille Flammarion, play their parts in this narrative. The fabric of these lives is a fascinating tapestry of the American and European societies of the thirty years surrounding the year 1900, when so much happened.

Why did I title this piece "The first Mars generation?" A new Mars generation has arisen, enthralled by the vision of Elon Musk, who wants to establish a colony on Mars with a million inhabitants. He hopes the first humans to reach mars will do so in the early or mid 2030's. Maybe it will work...

He placed us in the sky

kw: book reviews, nonfiction, biographies, mathematicians, astronomers

Sunday coming, in just a few days, will mark the 549^th birthday of Nicolaus Copernicus, or very close to it. Born Niklas Koppernigk in German-speaking Varmia, then part of Prussia, now part of Poland, he Latinized his name as an adult. He is the classic example of one who, while seldom straying a day's journey from home, roamed the cosmos in his mind, saw better than others how it worked (at least the local billion miles or so), and wrote the book that dragged the rest of educated humanity, kicking and screaming, into the new view. His book On the Revolutions of the Heavenly Spheres was only removed from the Roman Catholic Index of Prohibited Books 177 years ago, after a residence of more than two centuries.

There are partial biographies of Copernicus aplenty, but none other as accessible yet so thorough as A More Prefect Heaven: How Copernicus Revolutionized the Cosmos by Dava Sobel. One great value of the book is placing Copernicus in his milieu as a canon, an unordained church official, nonetheless required to live celibate. His official duties occupied much of his time and energy. Yet he was able to compile a great mass of observations, particularly of the Moon. He had as a primary ambition the desire to revise the Moon's orbit; the accepted orbit inherited from Ptolemy required the Moon's apparent size to vary by a factor of four, which it clearly does not do. He succeeded in this, and these and other calculations convinced him that the Sun, not Earth, was at the center of all orbits except the Moon's.

Secondly, from close reading of many of his letters and other writings, Ms Sobel is able to open a window into the thought processes that enabled Copernicus to unveil a sun-centered Solar system. Now that he has led the way, we expect every child to come to the same realization, to understand that the apparently solid ground under their feet is in fact rotating about an axis that spins both it and them at hundreds of miles (or km) per hour. Not only so, the yearly motion about the Sun requires a planetary velocity of about 66,000 mph, or nearly 110,000 kph. Copernicus did not know this latter figure, having no accurate parallax for the Sun, but he guessed its magnitude within a factor of about ten.

Parallax is the measurement of distance using trigonometry, by measuring the angular difference between measurements taken at different locations. Accurate measurements of stellar occultations and near misses by the Moon, taken by observers a few degrees apart in longitude (say, one in London and another in Paris, if both have a clear sky!) suffice to measure the Moon's parallax of about a degree (normalized to Earth's radius). That is, if one observer plots the Moon's position just at moonrise, at the same time a colleague plots its position while the moon is near the zenith—because the two observers are some 10,000 km apart—, their measurements will differ by about a degree. But the Sun is 400 times as far away as the moon, and naked-eye observations cannot discern a parallax of 1/400 degree, or nine arc-seconds.

As a church official, Copernicus knew there would be strong opposition to his model of the Universe. He knew as well as anyone the verses in the Bible that implied the Earth is "fixed forever" and that the Sun moved, except when Joshua commanded that it stand still long enough for a key battle to be finished. He published a short document that outlined his mathematical calculations using a new system with only 33 epicycles (Ptolemy had needed more than 100), without clearly stating that he believed the Earth was moving about the Sun. He delayed publishing anything further, until he was prodded by a Lutheran mathematician named Rheticus. Even then he dragged his feet and the book was only finished as he lay on his deathbed. He died at age seventy, having, perhaps, seen the last few pages of the book's galley proofs, but leaving it to others to proofread and complete. In April of 1543 the book was finished, and he died in May.

So carefully had the writing been done, and so hedged about with arguments intended to deflect scripture-based criticism, that it took the Holy Office of the Inquisition (established in 1542) 73 years to determine it belonged on the Index, and only as a book needing "correction", not wholly prohibited. The prohibition was dropped in 1835, after 219 years.

Concerning one fascinating bit of detective work, the author relates the work of Owen Gingerich, who studied about 600 copies of early editions of On the Revolutions (or De Revolutionibus, as it is frequently called). The book had three major editions and several minor ones, and was always printed with wide margins. Nearly every copy has copious notes, which indicates that anyone who thought enough of it to purchase a copy, read it carefully and checked calculations and thought about its implications. Interestingly, Johannes Kepler's copy has fewer annotations than most, but those that exist are very thorough and insightful. Nearly the only major scholar of the years prior to 1700 for whom a copy of the book is not known is Newton! Yet his work indicates he was familiar with it.

A word about production values. I love a book as well thought out as this, with such care taken to make the reading pleasant. The carefully-chosen quotes that begin each chapter, the archaic type face for chapter titles, and the decorated letter used in preference to a bare drop-capital, all indicate a fine historical sense.

One of my professors once remarked about such embellishments, nearly universal in well-produced 19^th Century books, that they showed the author had enjoyed the writing, and presaged an enjoyable reading experience. What a contrast to the dryness of most modern historical publications!

The Solar system begins to settle down

kw: book reviews, nonfiction, astronomy, astronomers, memoirs, planets

I grew up with nine planets, like nearly everyone alive today. I didn't learn any fancy mnemonic, but just learned the names right off: Mercury-Venus-Earth-Mars-Jupiter-Saturn-Uranus-Neptune-Pluto. From time to time over the years, a new estimate of the size of Pluto was announced. Once thought to be a very dark object the size of the Moon, it gradually shrank (and its albedo increased), finally settling down to a size of about 1,400 miles; the current figure from images by the Hubble Space Telescope is 1,430 miles or 2,302 km.

In recent years, the discovery of large objects (but smaller than Pluto) in the Kuiper Belt and beyond precipitated a discussion of Pluto's status: Is it a planet or not? (The Kuiper Belt is like the asteroid belt, but composed of icy bodies that are farther from the Sun than Neptune.)

As of mid-2006, Pluto is definitely not a planet; that is, it is defined as a "dwarf planet", a designation that always merits the quote marks, because semantically, "dwarf planet" means "planet of a smaller size" rather than "not a planet at all".

This image from the Wikimedia Commons shows the status of the "dwarf planets" found beyond Neptune as of 2008. Six of these were found by Mike Brown, who was also instrumental in the decision to demote Pluto, though he disagrees with "dwarf planet" at least as much as I do. His memoir How I Killed Pluto and Why It Had It Coming is a delightful romp through the life of a young astronomer who set out to "find a planet", and was known for just about a year as the first person to find a planet since the 1930s. Bigger than Pluto, and 2.5 times farther from the Sun, the body he provisionally called Xena was called the Tenth Planet for those heady months, until the IAU decided to define "planet" for the first time. It took a few tries to get it right.

The current definition, settled on as the book was being written, includes these factors:

• A planet circles the Sun, not any lesser body in the Solar System.
• A planet is large enough to have gravitationally settled into a sphere.
• A planet gravitationally dominates its orbit, sweeping it clear of other bodies.

There is a bit of a quibble about Trojan asteroids in Jupiter's orbit, and similar bodies in the L4 and L5 regions of other planets, but the fact remains that Pluto shares its orbital region with several bodies of similar size, so it is demoted from planet status based on the third factor.

The book tells two stories. One is the search for planets beyond Neptune, and the other is the courtship and marriage of the author to his wife Diane, and the early years of their daughter's life. Both stories reveal a human side of an astronomer's life that is seldom seen. Astronomy is by its nature a night job, though this has abated somewhat now that professional telescopes are computer driven and gather their images automatically. But if an astronomer is not staying up all night tending a telescope, the midnight oil still gets burned: studying the images, using the information they convey to locate earlier images that may reveal more facts about the object of interest, and tons of book work eat up huge amounts of time. A night's observations can require months to digest and analyze, and long hours are the norm if a scientist doesn't want to get scooped by someone else willing to work longer hours.

Xena eventually got renamed Eris, and a satellite around it was named Dysnomia. Eris is the goddess of discord, and the body is fittingly named for the squabbles that erupted once its discovery was announced. Since about 2008 the larger Pluto-like bodies have been called Plutoids, and a few hundred other Kuiper Belt objects (KBO's) are called Plutinos.

The author conjurs a fantastic image of an alien approaching the Solar System, and noticing first the four Giant planets, led by Jupiter. Then four smaller bodies are seen from closer in, that lie between Jupiter and the Sun (Earth is the third, but the alien doesn't know that). Finally, two bands composed of multitudes of bodies are discerned, one inwards of Jupiter, the asteroid belt, and one outwards of Neptune, the Kuiper belt (plus an outer region called the scattered disk). We then can realize that the eight planets, four big and four small, dominate the System; a few rounded bodies are the largest members of the two belts, and it remains to be seen whether the Kuiper belt plus scattered disk will yield up an even larger body, or several. Eris may have a big brother or two waiting to be found.

Solar System astronomy is healthy and exciting.

P.S. What it takes to find a new Plutoid.

1. A telescope with at least a meter aperture (Mike Brown used a 48-inch Schmidt at Palomar, first with film, later with digital sensors).
   
2. A wide-angle camera with 50-100 megapixels of sensor. This combination can record bodies of Magnitude 18-24 (Xena/Eris was M17 when found).
3. A half year to a year of observing time, mostly the half-month each month when the moon is the darkest and out of the way.
4. Fast computer power to compare the millions of points on one day's images with the next.
5. Gallons of midnight oil, so to speak, because the computer produces "possibles", which an expert human has to verify into a shorter list of "probables", and make extra observations to nail them down.
6. Time reserved on larger instruments, including the Hubble, if possible, for that nailing down process.
7. An accommodating spouse; you'll be traveling a lot.

P.P.S. Magnitudes. Take the time to read This Wikipedia article. Briefly, bright stars have small numbers as their Magnitude; "First magnitude" refers to bright stars. The dimmest stars visible to a young person in a dark sky have Magnitude 6 or 6.5. Magnitude is the negative logarithm of brightness, to the base of the fifth root of 100 (about 2.5), so a magnitude difference of 1 is a brightness ratio of 2.5:1 and a magnitude difference of 5 is a brightness ratio of 100. With a 10-inch diameter (250mm) telescope, the dimmest stars visible are magnitude 15. The brightest Plutinos have magnitudes of about 17 or 18, so they are very faint indeed. You'd need a telescope the size of a minibus to see one of them visually.

The sky for all

kw: book reviews, astronomy, virtual astronomy, astronomers, telescopes

In the title of yesterday's post about the Sloan Digital Sky Survey, I called the result the Galactipedia. The original vision for the SDSS was to take the spectra of a million galaxies, determine their redshift and thus their distance, and use that data to outline the large-scale structure of the Universe. The key figure in this effort is Jim Gunn, who had that original vision and eventually saw the SDSS through to completion.

Jim Gunn is the central figure of A Grand and Bold Thing, by Ann Finkbeiner, a blow-by-blow history of the SDSS and its hardware and software systems. Called Jim throughout the book (no doubt because he usually says, "Call me Jim"), Dr. Gunn, given time, might have done the whole thing himself. A premier instrument maker, his major material contribution to the survey telescope was the camera.

But this is not just about Jim Gunn. It is about the trend in astronomy, as in all the sciences, toward larger collaborations. While Jim abhorred the NASA "project over-management" method used to produce the Hubble Space Telescope and STScI (that's where the data goes), in the end, the effort now called SDSS duplicated the NASA model, because it had to. Long gone are the days of Lord Rosse building his giant six-foot-diameter telescope and surveying the heavens in splendid solitude. Big efforts become big projects, require big money, and need the complex interaction of big teams of people. A "lone ranger" is either brought to heel or becomes exiled, a "lone stranger".

Taking the spectra of a million galaxies in a finite time period, and storing them in a usable database, required imagining a telescope like none other before it; unique robotic controls; software to run the telescope, select targets (in groups of several hundred), store and manage and supply the data; and a human infrastructure to first produce and then tend all these systems. It is a good thing I already knew the outcome of the story, or I'd have been chewing my fingernails to the wrist at the unlikely series of troubles that plagued the project. Parts of the book read almost like cliff-hanger Perils of Pauline tales.

People don't behave. Astronomers in particular are all about the sky, tend to be loners, at least when at work, and are hard to manage. The software effort was huge, which means it required the services of a number of "superprogrammers". We used to call ourselves hackers when that was an honorable term. Superprogrammers are genuine lone ranger types, happier with machines than with people. The bane of any business manager, the most direction they will accept is "See that target? Hit it!". A manager'd better be quick, because they "Hit it" inordinately soon and immediately look for another target. There were targets aplenty as the SDSS project unfolded, and quite a bit of duplication of effort. Sometimes, there'd be two or three complete pieces of software, and they'd hold a benchmark (AKA face-off) test. The project burned through three Project Managers. But it did get completed.

Hardware doesn't behave. Both the mirrors for the telescope suffered near-catastrophic problems, which required much ingenuity (and extra money) to solve. The environment doesn't behave. Miller moths at the Apache Point site like to hide in tight, dark spaces, so they tend to grease the controls, then jam them.

One complication was money. Jim Gunn's initial guess was about $50,000 for a telescope and CCD camera, and the hope that he could afford lots of disks to hold the data. He was only off by a factor of about 1,000. Just the CCD's for the wide-field camera wound up costing $2 million. So he and the other astronomers learned to get along with the fund-raising establishment as the circle of donors and supporters was widened and widened again to raise $10 million, $20 million…I think the total cost to date approaches $100 million.

The telescope itself came to half a million. This is a story in itself. It isn't a huge telescope by modern standards, with a main mirror diameter of 2.5 m (98"). But a wide-field design requires optics a bit more costly than your typical Meade or Celestron star gazer. The field of view is about three degrees, and the CCD pack that covers this area takes a "picture" of about 200 Mpx. But getting light to focus well across the entire camera is daunting. Like all large-scale professional telescopes, including the Hubble and the two Keck 10m (34-foot) instruments, the design is Ritchey-Chrétien, or R-C. Older instruments with parabolic main mirrors and ordinary Cassegrain optics, such as the Mt. Wilson and Mt. Palomar telescopes, are considered passé.

Let's explore this just a bit. Here I step outside the book because R-C optics were not even mentioned. This diagram shows the classic Cassegrain optics as used at Palomar and in many amateur telescopes:


A parabolic mirror focuses on-axis light to a very sharp point. However, light coming at a slight angle, such as from any other part of an image, is not all focused to a point, but to a teardrop-shaped area. This kind of aberration is called coma. The secondary mirror increases the effective magnification of the system, but does not correct coma. A single-mirror system with an f/12 figure, and a Cassegrain system with an f/4 primary and a 3x secondary, will have exactly the same level of coma distortion in an image.

A Ritchey–Chrétien system looks exactly like a Cassegrain system to the eye, but there is a subtle difference. The primary is not parabolic, but hyperbolic, and the curvature of the secondary, while still hyperbolic, is matched to the primary in a way that eliminates coma. However, the smallest focal point is not quite as sharp as it is with the Cassegrain, but it is still very small, and is the same over a large area, three degrees in the case of the Sloan telescope. As we'll see, the images it produces are quite spectacular, and plenty "sharp enough". And the bottom line? Making that hyperbolic optical system cost much, much more than a parabolic one. But it is just so darn much better for modern astronomical needs that it is used for all professional telescopes since the 1950s.

The power of the SDSS is that all the data are public, and include an almost game-like interface for looking at images and retrieving data. As I noted yesterday, the SDSS maintains a SkyServer web site for viewing images and getting data.


This shows the galaxy known as M109, the 109^th object in the Messier Catalog of objects that Charles Messier wanted to remember so he would not confuse them with comets. He was primarily a comet hunter. For this screen shot I opted to show objects that have had their spectra recorded. Note that M109 is not among them. It is much too close. The Sloan survey is intended to look at large-scale structure as outlined by distant galaxies. The Xes mark fourteen galaxies that you can hardly see at this scale. Their spectra tell their distance and other interesting facts. All this can be downloaded, either one-by-one or in whole reams of data.

If you want to "spelunk the sky" and see neat stuff, it isn't hard to do. If you want to do more and be a "Sloan Astronomer" (my term), make sure you have plenty of disk available. The entire SDSS archive currently comes to 40TBy (that's 40,000 GBy). It covers a quarter of the total sky, centered on the North Galactic Pole. Not just (more than!) a million galaxies, but spectral data on hundreds of thousands of stars is also included.

It is the second-largest data repository I know of; Google Earth at about 3 PBy (3,000 TBy) is the largest. But Google Earth provides an even easier way to view the sky. There is a Google Sky option in Google Earth, which uses the Sloan and other sources to map the sky and make it viewable and searchable. It was even quicker for me to find M109 in Google Sky than it was in SkyServer. If you are interested in some particular kind of star or galaxy, SkyServer has suggested projects and tutorials on how to do the work.

The book is a great example of a contemporary history. The author's Reference section begins with a five page list of interviews she conducted. The list of published works is correspondingly shorter. There hasn't been time for many of the principals to decide their experiences warrant a memoir. But it is all the more immediate for it. I imagine our view of the American Revolution would be significantly different if a historian could interview Washington and Adams and others. To me, the establishment of this virtual sky and the tools to easily use it is almost as revolutionary as the founding of a nation. One need not apply a year in advance for two or three observing nights on an overbooked large telescope and hope you don't get rained out.

Thousands of professional journal articles have been authored as a result of the SDSS and its current data release, called DR7. And what do I hope for next? A clone of the Sloan telescope and camera situated in southern Chile, which could double the total sky coverage.