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I still have never seen Sagan’s Cosmos

The Cosmic Connection: an Extraterrestrial Perspective

By Carl Sagan 

15 Mar, 2015

Because My Tears Are Delicious To You


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For persons of a certain time and place, to think of Carl Sagan is to remember his popular TV series Cosmos [link] (recently rebooted by Neil DeGrasse Tyson. As it happens, I’ve never seen Sagan’s Cosmos. I know him as an author of science popularizations (and one mediocre SF novel), and as a sort of a lesser Asimov or Ley.

The book I’m reviewing today is the first Sagan book I ever read. 

Science marches on, hence this collection of essays, many of which blew my mind back when I was fourteen, no longer documents cutting edge research and ideas. However, it does give us a snapshot of science as it was at a particular moment in time, a time when space probes had just begun to illuminate the many worlds of the solar system. If Sagan were still alive, I don’t think he’d particularly mind that his avant-garde pop science is now dated; a large part of the book documents the continuing exploration that has transformed this book into an interesting historical document. 

Context: assuming that the ISFDB is correct [1], the hardcover of which my scuffed book is the mass market paperback reprint was published in November of 1973. Mariner 9, the first probe to successfully orbit Mars, had done so only two years previously, following Mariner 4’s flyby mission by six years. Venus, a somewhat easier target, had had its first flyby in 1961 (the first flyby with data returned was in 1962) and its first lander in 1970, although (somewhat counter-intuitively) it would not get an orbiter until 1975. Pioneer 10 had traversed the asteroid belt but would not reach Jupiter until just after the publication of this book.

Basically, there was not a lot of detailed information about the other worlds of the Solar System and a lot of it was of very recent vintage in 1973.


Preface (The Cosmic Connection: an Extraterrestrial Perspective):

A short preface that explains Sagan’s long interest in astronomy, as well providing an outline of the book’s organization. Sagan acknowledges that he lives in a remarkable period, a time when effective human exploration of the Solar System is just beginning.

The main body of the book is only 267 pages long and there are 39 essays. Even though I have allowed myself to ramble at greater length than usual, I have tried to be brief when I can. Most of my synopses of Sagan’s essays are short. Some border on being epigrams.

Part One: Cosmic Perspectives

A Transitional Animal:

Sagan puts humanity in its place as merely one of the latest organisms to pop up on Earth. It is not the goal at which Earth has been aiming nor will it be the final organism to evolve. Life on Earth is billions of years old and Earth will continue to be life-bearing for billions of years to come.

Exactly how much longer life can survive on Earth before the slow and inexorable brightening of the Sun pushes the planet into runaway greenhouse heating is the subject of some debate. I believe the current consensus is that the Earth has less time than Sagan believed. However, his main point still stands.

The Unicorn of Cetus

Using a three dimensional model of the interstellar region near the Sun, Sagan explains what the sky would look like from Alpha Centauri. He then points out that the sun, despite being brighter than 90% of the stars in the Milky Way, stops being naked-eye-visible at a distance of only a few dozen light years away, which is a very short distance on the galactic scale.

A Message From Earth:

Sagan discusses (very briefly!) the plaque on Pioneer 10, a plaque intended to serve as a message from Earth to whoever or whatever finds the probe out in interstellar space. The plague not only identifies where the probe is from but when, with a fair degree of precision.

Oh, the two humans on the plaque are naked. If nakedness offends you, I sure hope you haven’t looked at the picture. 

Of course, Pioneer 10 was lobbed into interstellar space and not at any other stellar system. It would have to be retrieved by some culture capable of interstellar flight.

A Message To Earth:

The first technological species to encounter the Pioneer 10 plaque was, of course, humanity. Sagan details some of the many reactions, ranging from puritanical outrage because the two figures are nekked as jaybirds, critical commentary from feminists who didn’t care for how the female figure seemed to be passive, critiques from anatomists, and complaints from scientists who didn’t think the message was as clear as its designers intended it to be. Sagan also admits the two figures fall a bit short of including features from all the major varieties of humans; the man was supposed to have a short Afro. 

I am just a little surprised NASA tried to be inclusive this early in their history, although there was a black astronaut in the 1960s. (Robert Lawrence, and he is not better known because he was killed in a flight mishap in 1968. The first African American in space was Guion Bluford, who orbited in 1983.)

Experiments in Utopias:

Given the many possible crises facing humanity, Sagan suggests that rather than discouraging social experimentation, we should encourage it.

Today we know most challenges can be met with draconian laws inconsistently enforced, longer jail terms, and tax breaks for the rich. It’s pretty much what Sagan would have wanted.


Sagan implores the scientists of the world not to be blinded by the nature of life as we know it (which is to say, terrestrial life). While we know for certain life can exist in terrestrial conditions, that does not mean it cannot develop and evolve under other conditions as well. 

Space Exploration as a Human Enterprise: I. The Scientific Interest:

Sagan outlines some of the scientific benefits of space exploration, including the possibility that study of worlds like Venus could better inform us about how Earth’s climate will change over time. It is quite possible that the greatest benefits will come as complete surprises to us.

Space Exploration as a Human Enterprise: II. The Public Interest:

Sagan wrestles with the cultural impact of exploration, from the effects of the Earthrise photo 

to the possibility that Earth’s militaries could be distracted from shooting each other by refocusing them on the complex task of exploring the solar system, a task that could potentially suck up as much money as the military industrial complex and so not threaten to put any MIC plutocrats out of work.

As Sagan points out over and over, the cost of space programs tends to be comparable to the cost overruns on various military programs.

Space Exploration as a Human Enterprise: III. The Historical Interest:

Sagan tries to justify space exploration by drawing parallels with prosperous societies whose intellectual and economic blooming coincided with a period of exploration on Earth. 

Part Two: The Solar System

On Teaching the First Grade:

Sagan relates how his attempt to wow a class full of kids with an introduction of the scientific method was sabotaged by the fact the kids were already very well informed.

Even in the 1970s, any essay about students whose point wasn’t kids are lazy and stupid and poorly educated and THEIR MUSIC IS JUST NOISE” was pretty unusual. 

The Ancient and Legendary Gods of Old”:

Sagan relates an interesting letter he received from a man who had himself committed to an insane asylum to better search for the retired gods the fellow believed are all around us. Inspirationally, he was successful as he soon discovered any number of his fellow inmates admitted to being gods.

The Venus Detective Story:

Sagan details how during the 1950s and 1960s scientists slowly came to understand that Venus is not Earth’s twin (as it was once fantasized to be) but rather an unpleasant, even hellish place.

This would be one of the snapshots of Science! In! Action! Confronted with information that contradicts what they thought to be true about Venus, scientists changed their models. Slowly, and sometimes incorrectly, but slowly converging on a less inaccurate model.

Huh. So this is where I got the first German bomb on Leningrad killed the only elephant in the zoo” factoid, although I usually misremember it as first German artillery shell and Stalingrad.

Venus Is Hell:

Sagan describes Venus as it was understood in the early 1970s. While he admits conditions on Venus are such that the chemistry on which Terran life depends would fall apart, he points out that this does not rule out other, more robust biochemistries.

Sadly, there’s no evidence that Sagan’s speculative biology has any relationship to reality.

Science and Intelligence”:

Sagan relates an encounter with a particularly clumsy and crass member of one of the United States’ many, many, many secret police forces. 

Thank goodness the end the Cold War meant an end to this sort of ineffective, counter-productive intelligence gathering.

The Moons of Barsoom:

Sagan relates how, with the aid of space probes, the two moons of Mars went from dimensionless spots of light on photographic plates to tiny worlds about which humanity knows something. 

The image that for me most exemplifies the great strides we have made since the events detailed in this book is an blurry image of Phobos. It’s low resolution because it’s a copy of a Polaroid photo someone took of an unprocessed image on a computer monitor screen. It’s like seeing a Vermeer painting of the first landing on the Moon. Wait, no. That would be too good. It’s like seeing a Rob Liefeld illustration of the first moon landing.

The Mountains of Mars: I. The Observation From Earth:

This is a very brief history of humanity’s struggle to properly model Mars. As Sagan points out, perfectly reasonable models (including some of Sagan’s own work) had to be discarded in light of information that revealed scientists had it wrong.

The Mountains of Mars: II. The Observation From Space:

Sagan relates what was thought to be true of Mars in light of information from Mariner 9. Mars turns out to be very different from what humans had imagined it to be.

Like most moderates, I believe that sending yet more probes and landers to Mars, the second most boring world in the inner solar system, is terribly misguided. Why, far more interesting worlds orbit Saturn and to a lesser extent Jupiter! Anyone who does not share my perfectly reasonable belief must certainly be a deviant of some kind. Still, Sagan is a perfectly endearing Mars pervert as he enthuses over what is by modern standards a very small collection of new data. Of course, Mars is a total waste of time … but he can’t see that. 

The Canals of Mars:

Sagan contrasts pre-space-probe models of Mars with post-Mariner‑9 models. He notes that it is possible that Mars’ climate varies wildly over comparatively brief periods and we just happen to be looking at Mars during an airless icebox phase. Whatever the truth, he is very interested to see what future probes reveal about Mars. 

I would not be surprised at all if John Varley’s In the Hall of the Martian Kings” was inspired by this essay. It’s so interesting to see someone who finds the New Solar System fascinating and inspirational, rather than skiffy fans who lament that “[…] the first Mariners and Veneras ruined things for us.”

The Lost Pictures of Mars:

Sagan relates how a cost saving of about $30,000 in space probe design cost the US a dozen precious photos of Mars. 

Has Mariner 9 crashed on Mars yet? Sagan estimates it should remain in orbit until some time around 2020. Of course, technology has marched on and even if the remaining Mariner 9 photos could be salvaged, they would be of historical interest only.

The Ice Age and the Cauldron:

Climate was a complex and poorly understood subject at the time. It was known that the climate had changed in the past and could change radically in the future. Climate change could have a profound effect on species native to Earth, species like humans. Since the net effect on climate of human inputs could not be predicted in the early 1970s, Sagan calls for more research. 

Well, that seems uncontroversial enough. I wonder what ever happened with that proposal?

The Beginnings and Ends of the Earth:

The Sun has been slowly becoming brighter with time, one implication of which is that one day the Earth’s oceans will boil and all life on Earth will perish (Mars will be warming up, so it is not all bad). An interesting question raised by this is: if the Sun was so much dimmer in the past, how is it that conditions on Earth appear to have remained within a fairly narrow temperature range for so much of its history? Sagan raises the possibility that the young Earth had more greenhouse gases in its atmosphere.

Terraforming the Planets:

Sagan speculates about ways to make the various terrestrial worlds of the Solar System more habitable.

I notice that whereas Sagan is actually fairly cautious about the prospect of terraforming Venus, by the time his ideas filtered over to Jerry Pournelle they had somehow become yeah, totally trivial matter of dropping algae into the upper atmosphere.” I am sad to say that Sagan probably grossly underestimated the necessary time scale, although nowhere nearly as badly as Pournelle did in A Step Further Out” (which I totally own, if anyone has spare cash and wants a review). 

The Exploration and Utilization of the Solar System

Sagan outlines future Solar System research possibilities, but also points out various challenges that could slow progress. 

While danger from contamination of Earth by opportunistic alien organisms” is mentioned, he overlooks this just isn’t high priority for most people, which means that funding is going to be a serious constraint.” The US did manage a golden age of space probes for a time, but that is drawing to its inevitable end as I type. One hopes other nations will continue to increase their activities in space. One also hopes that Sagan’s estimate that it would take two or three centuries to explore the Solar System isn’t too optimistic.

Part Three: Beyond the Solar System

Some of My Best Friends Are Dolphins:

And some of those dolphins are total perverts. Actually, I think this is another example of a field where science marched on: dolphins have turned out to be much less likable animals than we thought they were in 1973. Still fascinating animals, however.

Hello, Central Casting? Send Me Twenty Extraterrestrials”

Sagan recounts how he was consulted on the issue of how aliens should be depicted in 2001: A Space Odyssey.

The Cosmic Connection:

This is basically an early run at the we are all starstuff” speech. We are intimately connected to the stars because the heavy elements from which we are composed were all cooked up in heavy stars.

Extraterrestrial Life: An Idea Whose Time Has Come:

Despite the revelation that the Solar System is filled with hellworlds, Sagan is optimistic not just that life could exist elsewhere, but that the human capacity to find and recognize that life would only improve in the decades to come.

It’s interesting to revisit his speculations on other stellar systems; they are now just as obsolete as early 20th century models of Mars were by 1973. That’s not a criticism.

Has the Earth Been Visited?:

After citing the evidence (nil) and discussing the arguments against any such possibility, Sagan concludes that it seems unlikely Earth has ever been visited.

I would like to see the math for some of these arguments, in particular Hong-Yee Chiu’s suggestion that one UFO visiting Earth a year implies as much metal tied up in UFOs as would be found in a half million stars. I don’t disagree with the conclusion, it’s just that I’m not sure the route he took to get there is rigorous.

A Search Strategy For Detecting Extraterrestrial Intelligence:

Sagan examines the question of how to look for other civilizations and comes to the conclusion that not only are there promising avenues of research, they are cheap enough the merely rich could fund them. Governments need not be involved. 

If We Succeed…:

Sagan outlines some of the benefits that could come from discovering other civilizations, which as he points out would almost certainly be much older than our civilization (because if they were much less advanced than we are, we’d never see them). He also points out that even if announcing our presence is a bad idea, it’s much too late to do anything about it: our radio and TV noise is already telling the nearer stars about us.

I think subsequent research suggests our signals become noise very close to the Solar System, although who is to say how good an ancient civilization can be at squeezing information out of noise?

Cables, Drums and Seashells:

Sagan discusses the possibility that we might lack the ability to detect or imagine the channels by which other civilizations talk to each other. It does no good to look for Galactic Usenet on the 21 cm band if everyone out there is using phased neutrinos or tachyons or something much weirder.

The Night Freight to the Stars:

Crewed space travel would be awesome. AWESOME!


Looking for aliens by looking for evidence that they have re-engineered entire solar systems.

Currently we know of no existing Dyson Spheres, but then, we only know where they not exist. There’s a whole unexplored universe out there. Given this application of a Dyson Sphere it is just as well that we haven’t encountered one yet.

Twenty Questions: A Classification of Cosmic Civilization

How to categorize civilizations by energy and information use.

Sagan’s numbers in this seem oddly … off. He gives the power output of the Earth as between 1015 to 1016 watts; he seems to mean artificial power. Surely that’s too high? He estimates a low resolution picture might have a million bits; that seems high as well.

Galactic Cultural Exchange:

The age of the universe and speed of light limitation limit the degree to which cultural homogenization can occur across the universe. A galaxy might be home to one unified civilization, but beyond that the time scales become intractable.

A Passage to Elsewhen:

Relativity means that a civilization with access to enough energy could send people to the far future.

There is also a certain small element of Black Holes! Let’s speculate about using them for transportation purposes!” that Sagan will develop further later in the book. Because it was the 1970s and black holes were still as cool as digital watches and four-function calculators.

Starfolk: I. A Fable:

We are not just starstuff but starstuff that thinks about being starstuff. DID I BLOW YOUR MIND?

I feel badly that this is no longer as awesome as it should be.

Starfolk: II. A Future:

A brief account of how stars live and die and how that relates to our existence.

Starfolk: III. The Cosmic Cheshire Cats

Maybe flying into a black hole isn’t instant tidal death but a way to reach distant locations! Maybe there could be civilizations using black holes for FTL travel and relativistic travel to visit the provinces! Maybe this is the chapter that inspired Joan D. Vinge’s The Snow Queen! 

I remember when SF authors found science inspirational rather than an affront to their youthful expectations.

I loved the idea he sketches out here but not only do I suspect that flying into a black hole, even a very large one, is unlikely to result in cheap, fast interstellar travel — the more I learn about physics the less optimistic I am about NAFAL spacecraft. 

Although this book is just popular science, there is a proper index. I am not saying that there should be a death penalty for people who create index-free non-fiction books, I am just saying I don’t strongly oppose it.

Something that surprised me when I revisited this was the art, which is entirely black and white. I think I would have put money on there being colour plates in this and I would have lost that money. In 1973, black and white photos and drawings were good enough.


I don’t know if this book this would have any appeal to younger readers. For this older reader, it was interesting to reread what was in its day a very popular work. I was reminded of how comparatively little we knew back then — which is something Sagan freely acknowledges. 

Sagan’s enthusiasm for the process of superseding his own work is quite infectious. I would hope that were I revisit some analogous work published in 2015 in 2057, it took will look just as quaint as this work now does. 

Of course, it would be even nicer if I were still here in 2057

1: The book’s own copyright page is sadly vague as to the exact date of the first printing.