Carl Sagan, PALE BLUE DOT (1994), post 2

I posted about my favorite two parts of this book a week ago, in this post, and today will post a complete outline of the book based on my notes as I read, somewhat edited and slimmed down.


  • We’ve always been wanderers, for 99.9% of our history. On earth, there’s no place left to explore. But our ancestors noticed 5 moving “stars.” In recent decades we’ve begun to explore them.
  • The plan of this book is: examine claims from history that our world and species are unique, even central to the cosmos; examine the solar system and assess reasons for sending humans into space; then, imagine our long-term future in space.

Ch1, You Are Here

  • About the February 1990 picture of Earth from Voyager 1 – the famous pale blue dot. (Discussed in earlier post.)

Ch2, Aberrations of Light

  • Now try to imagine that the entire Universe was created for one species on that blue dot, or one shade of that species, or ethnic or religious subdivision. Suppose someone made such a claim about a different dot?
  • It seems natural to us that our own group should be in a central position. The ancients assumed Earth at the center of the universe. There was little counterevidence. The heavens were thought perfect, different than the earth. These were opinions, without evidence; no one cared.
  • The change began with Copernicus, though his ideas were considered mere convenience for calculations, lest the truth of scripture be challenged. Then Galileo observed Jupiter’s moons, the phases of Mercury and Venus, and suggested that nature can be observed. He was threatened by the church. It wasn’t until 1837 that parallax was finally observed to show the earth circled the sun. by the late 20th century we’ve verified all of this via probes to the planets.

Ch3, The Great Demotions

  • (This chapter summarized in earlier post)

Ch4, A Universe Not Made for Us

  • Quote from Arnold’s “Dover Beach”
  • The clash between science and the church began with Galileo in 1633. The church now considers itself infallible, the only true religion, not to be reconciled with progress and modern civilization. Science makes people nervous; if the church could not be trusted to be literal about matters of the sun and earth, what else could be doubted?
  • More recently debates about moral codes. Do we want comfort? Reassuring fables? Examples from Shaw and Appleyard. The latter longs for religion, even that different religions cannot war with one another. But what’s the alternative? Author dismisses his writing as “the anguished cry of the infant when the Parent does not come.” Are we not to correct our errors?
  • Ideas that were common 2 or 3 millennia ago cannot be supported today. But this erodes confidence, our need to have a purpose. We lack consensus about our place in the universe. Don’t we need myth and ritual? But our new perspective outweighs the losses. 53b. We have less to be afraid of, 55. We thus have more hope. And the discoveries about the universe we’ve made have led to most of the technology of the modern world.
  • It may seem satisfying to believe the ancient story about the forbidden tree of knowledge, etc.. But as we keep perceiving design, we discover natural processes that produce such regularities. We are the custodians of our own meaning. There is no Parent to take care of us.
  • What goal could we find as a cosmic purpose?

Ch5, Is There Intelligent Life on Earth?

  • In our big cities the natural world has almost disappeared. But we exist only within a thin film of life along the surface of the Earth.
  • Photos of the Earth from space from a distance show no signs of life. How would an alien explorer deduce anything about life on Earth, via a flyby? You could deduce that the oceans are water. And lots of oxygen in the air. And maybe life to break apart the oxygen? Other gases; the greenhouse effect. And methane, must be from life. And radio waves, of certain frequencies. Intelligent life? At higher resolutions, still no sign of life.
  • But at 100-meter resolution, everything changes. Agricultural grids. Circular irrigation systems. Grids in streets in cities. And beings [i.e. cars] that run along these streets, and sometimes retire to little houses. At night, illumination. City lights; burning oil; fishing fleets. Forest fires. You also detect carbon dioxide being spewed into the atmosphere. Signs of ecological damage. The environment is being destroyed. Is there really intelligent life on earth after all?
  • Sidebar p78: How author worked on Galileo probe in 1990, which so far has detected to similar signs of life in the solar system.

Ch6, The Triumph of Voyager

  • NASA offers the sort of vision we’d like to offer our children. In the ‘80s and ‘90s NASA suffered a string of catastrophes. Yet there were also triumphs. But are ‘manned’ flights really necessary? First consider what robot craft have done.
  • Voyagers 1 and 2 were the trailblazers. Map p85. Launched in 1977. Used gravity assist. And a rare alignment of the planets. Jupiter, Saturn, Uranus, Neptune; photos p86ff. Jupiter’s rings. Active volcanoes. Some false colors in photos. Jupiter was described in Cosmos; others discussed here. Description of spacecraft. There were problems in flight, p94. The engineers saved the day, more than once. Having to swivel the camera during flybys of the outer planets. Predicts data from them through 2015. Unlike many government projects, the two spacecraft came in at cost and on time. The cost was a penny a year for each American, each year until Neptune.

Ch7, Among the Moons of Saturn

  • On earth the origin of life began some 4bya. Where did complex molecules come from?
  • The closest we have in the solar system to an early earth is Titan. But it’s very cold. Its atmosphere was discovered back in 1944. A deep red atmosphere. Author studied it under Kuiper. Could Titan be creating organic molecules today? Simple organic molecules were found by the Voyagers. Some of its chemistry has been determined, but little more is known. It’s subject to tidal forces, so likely all ocean or all land. Author imagines the Huygens probe entering and landing on Titan. [[ This happened in 2005 ]] Planned for the Cassini spacecraft, launched in 1997. [[ This happened too: ]]

Ch8, The First New Planet

  • How the five planets, and the sun and moon, were named after various civilizations’ gods. The week was assigned seven days, after those seven, with familiar names. Though the order wasn’t known. But the number seven has permeated culture. P123. Thus Jupiter’s four moons were rejected; later a 7th actual planet was thought necessary. Numerological mysticism. Perfect numbers. The next real planet discovered was Uranus. Unlike the other giants it has no source of internal heat. It ‘lies’ on its side with respect to its orbit. And it has rings. And five moons.
  • In 1986 Voyager 2 reached the Uranus system. … Many pictures, etc. p132.

Ch9, An American Ship at the Frontiers of the Solar System

  • Then Voyager 2 headed to Neptune, a planet which hasn’t yet circled the sun since discovered. It also has rings, and a big moon called Triton; we can see its surface. Craters look very new. Both Titan and Triton may be the same kind of objects as Pluto, not yet visited.
  • Beyond them are minor planets, or inactive comets. If there are planets beyond, they haven’t been detected. But they can’t be just past Neptune, or they would disrupt its orbit.
  • But far beyond Neptune and Pluto might be planets of other stars. They might be detected using an occulting device to block light from the star. Or by a wobbling motion of the star. One system has been found around a pulsar, 146m. Three planets, all very close. [[ Of course as of now thousands of exoplanets have been discovered: ]]
  • Voyager found no signs of life. What we do see all has ordinary explanations—but we might be wrong.
  • The Voyagers are now bound for the stars. See diagram p150, with the heliopause. The boundary of the solar system can be defined in different ways. The craft won’t pass through the Oort cloud for another 20,000 years. Might they someday be found by an alien civilization? Thus the Voyager records. Even if the records aren’t understood, the craft themselves are messages. Likely they’ll exist past the lifetime of the Earth.

Ch10, Sacred Black

  • (Photo: good edge-on view of earth’s atmosphere w/thunderheads)
  • People on earth are accustomed to a blue sky. But what is the sky? It wasn’t until 1957 that anyone rose high enough, 100,000 feet, to see a purple sky. And Yuri Gagarin saw a black sky, 1961. So the blue must have something to do with the air. And so on: white light from the sun, scattering of light in the atmosphere. We can speculate about the skies of other planets and moons. Venus, yellow-orange. Mars, reddish. Below the clouds on the giant planets, black. And now we are sending balloons and landers…

Ch11, Evening and Morning Star

  • The “evening star” and “morning star” was Venus, not realized to be a world. Seen after sunset or before sunrise. It has phases. Mariners 1 and 2 visited in 1960 and 1961. But not with cameras. Later Galileo did a flyby and mapped parts of the surface. And other craft went into orbit, with radar.
  • Early speculation imagined Venus, a planet about the size of Earth, much like it, underneath the clouds, perhaps with swamps. [[ Much science fiction was written especially in the 1930s and ‘40s and early ‘50s depicting Venus as a hot, swamp-covered, cloud-covered world. ]] Until 1956, when evidence revealed a temperature of some 300C. Explanations were offered. In 1967 the Venera 4 dropped a capsule onto Venus. Venus is hot and dense, nothing habitable. Later craft expanded our knowledge. Mariner 2 is still out there, orbiting the sun.

Ch12, The Ground Melts

  • On Earth we find volcanoes. Some with calderas. Every once in a while one explodes. The lava reveals the interior of the earth is very hot. Mountains erode in about 10my, so they must be built up at the same rate. [[ footnote 187 makes good point about scale ]]
  • It was once debated whether the craters on the moon were volcanoes or impacts. In 1971 Mariner 9 spotted huge volcanos on Mars. Some are very old, others relatively new. Magellan in 1990-1993 provided data to prepare maps of Venus. There are only a few impact craters on Venus.
  • Then Io, seen by Voyager 1 in 1979, covered by volcanos. Perhaps not molten rock, but sulfur dioxide and molten sulfur. … Someday there may be a general theory of vulcanism.

Ch13, The Gift of Apollo

  • Recalls how the Apollo 11 astronauts bounced slowly, dreamlike. The moon has long had a place in human mythology and history. Examples of terms and phrases. Some thought going to the moon was faked; others thought it sacrilege. No one has been back since 1972. Why did we turn back? Apollo was really a gesture about politics, not science. It was about rockets that could also be used in warfare. Testimony about spending the money, 1958. The plaque that said “we came in peace for all mankind” was ironic given wars currently underway. As soon as a few missions got there (and the first scientist), the program was cancelled. Still, some science was done. And its success enabled the many unmanned craft that followed. It captured the imagination of the world. And awakened a slumbering planetary consciousness. A perspective that may save the world.

Ch14, Exploring Other Worlds and Protecting This One

  • How the Earth appears from space, and from a distance. Knowing only one world, we don’t know what else is possible. We’ve now begun comparative planetology. We’ve discovered three potential environmental catastrophes: ozone layer depletion; greenhouse warming; and nuclear winter. All three have ties to planetary exploration. First, about CFCs; connections to Venus and Mars. No ozone on Mars. Second, burning of fossil fuels and carbon dioxide. Can we deduce through models the climates of other planets? The prime example is Venus. (Author notes that some who dispute this idea “call themselves conservatives.” P227) Third, the consequences of nuclear war. The idea first named in 1982/83, by a group including the author.
  • Earth and space sciences have the greatest international cooperation of any field of science.

Ch15, The Gates of the Wonder World Open

  • There will be a nation, or consortium of nations, that will begin the next venture of humans into space. To Mars? Nearest, but cold. The landscape suggests water was once on the surface, until about 3.8bya. Photos 234-5.
  • Meteorites are fragments of other worlds. Some have gasses trapped inside – even the atmosphere of Mars. And evidence of water. Only 10 known. A drop of water extracted from one. Is it possible life could have been transplanted from Mars to Earth? Life was once thought common on Mars, but we’ve found nothing. Tests on Viking have been inconclusive. And yet, why would Mars, similar to earth, be lifeless? It would be simpler and cheaper to send robots to Mars to find this out.
  • In 1993 the Mars Observer went missing; it was the first US mission to Mars since 1976. But there has been a wide range of missions attempted by the US and Soviet Union. P246, with ever rising success curves. Yet failure rates still lie around 30-40%. At least with robots, no lives were lost. And spacecraft could be redundant, sent in pairs. Many more countries plan missions.
  • And rovers on Mars. VR helmets. What would be the justification to send people? Perhaps cooperation between nations. At one point Gorbachev was convinced. But not Reagan. Later various ideas were floated, including a space station. Yet suspicions remained.
  • Yet if we’re not sending people to Mars, what’s a space station for? Technology is always risky, yet there will also be volunteers. Why not then the moon? But it’s probably a dead end. Other propulsion systems may change what’s possible. But someday a manned ship to Mars might be sent… It’s bound to happen. And ride around on a rover, exploring Mars.

Ch16, Scaling Heaven

  • After so much progress, are we daunted by a voyage to Mars? Or do we take care of people on Earth? Or can we do both?
  • People have lost interest, it seems. Though Bush proposed a long-term direction for NASA leading to humans on Marsh in 2019. Then foundered. Concerns; costs. Political issues of keeping it going over multiple administrations. It would have to be quick and cheap.
  • Of course there are many other things to spend money on, 269t. There must be some ‘line’ across which it would not be prudent to spend so much money. It should apply to defense, too.
  • Could there be a profit lure? Heinlein’s “The Man Who Sold the Moon” (from 1950) used a lure by faking diamond finds on the moon. Actual diamonds, on Mars perhaps, might do it.
  • What other benefits might there be? Knowledge of our planet; pursuit of basic knowledge; spinoff technologies. The ‘multiplier’ idea was a delusion, 273.4. Helium-3; reduced population. No.
  • Author would propose funding projects worthy on their own that would also contribute to human space missions.
  • Astronauts on a space station for lengths of time. Trying out ‘artificial gravity’ on such a station. Studies of the sun. development of heavy rocket technology. Joint projects with Japan and other nations. Develop robots, balloons, and aircraft for Martian exploration. Technologies to make fuel out of Martian minerals. Constant thrust propulsion. Study of near-Earth asteroids. And so on.
  • And there are less tangible arguments. An increased cosmic perspective. Support is high for big missions. The very idea of flying; a primitive urging. Just seeing jets take off. Quotes from Rousseau and Russell.

Ch17, Routine Interplanetary Violence

  • Galileo saw ‘handles’ on Saturn and died without realizing what they were. The realization they were rings, resulting from collisions, had grave implications. Much later, it was discovered that all the giant planets have rings. Maybe formed by tidal stresses; or by collisions. Sometimes debris reforms; if too close it cannot. Presumably there were many more collisions in early history of the solar system than lately. The Moon was likely formed when a Mars-sized world struck the Earth. And now we have asteroids, comets, small moons. We’ve visited some asteroids, e.g. Gaspra, p297, about the size of LA. Comets pass by, like Halley’s. Shoemaker-Levy was actually a string of 9 comets, torn apart by Jupiter, then colliding with Jupiter. A once in a dozen lifetimes event. 1994. What would be seen? Finally fireballs were seen. P302ff. And huge bright plumes. P304.
  • There are some 200 “near-Earth” asteroids. Some of them are bound to hit the earth. It might be possible to travel to some.

Ch18, The Marsh of Camarina

  • Camarina was a city in southern Sicily, threatened by pestilence, until a marsh was drained. But that allowed invaders to come in and slaughter the entire city.
  • The Cretaceous-Tertiary collision, hitting in Yucatan, killed all the dinosaurs and 75% of all other species. Smaller objects hit with regular frequency. Diagram p313. Plans were made to identify and track them. Other plans were made to use them as weapons. Or how to deflect one heading to Earth. Using rocket engines, or nuclear bombs. Example of an asteroid that will come close in 2070, perhaps to be called Nemesis. Another idea, to move asteroids into earth orbit, to mine. But beware potential weapons that “only a madman” would use. There are such madmen, p321. Like some others, this technology might be too dangerous to develop. But eventually it may be done.
  • We can speculate similar issues in other planetary systems. Without technology, and political unification, intelligent beings on those worlds may not survive very long.

Ch19, Remaking the Planets

  • The science fiction writer Jack Williamson, in the 2nd world war, imagined a future populated solar system. With different planets settled by different countries. The story was “Collison course,” published in Astounding July 1942. The plot concerned colliding asteroids. He imagined terraforming, and paragravity. Anti-matter. Used to move asteroids around. A more plausible source of energy is fusion, used by the sun.
  • Could we live on Mars? Possibly, with large subsidies. Eventually accessible by ordinary folks. Can the planets be terraformed? We’re certainly altering our own planet. But it’s easier to destroy than to build. Author’s 1961 article; then taken up by SF writers. The issues about terraforming the planets summarized, p342ff. Opposite problems on Venus and Mars. Not enough greenhouse effect on Mars. Then the moons of Jupiter and Saturn. Titan, perhaps. We will need to understand these worlds first. And balance issues about benefits against costs, and our rights to alter other worlds. We need to guarantee the habitability of Earth first.

Ch20, Darkness

  • We are frightened of the dark, but away from a sun, most of the universe is dark. Is ours the only inhabited planet? We can communicate across the dark—with radio. If aliens exist, our civilizations would almost certainly not be in lockstep. But we could try communicating. Some fear the idea, for various reasons. It would be only to listen, not respond. It’s unlikely they will want to eat us. We are now already listening for such signals. SETI. Begun in 1960; some false alarms. After 30 years, the Planetary Society took it over, with support from Steven Spielberg. Two META facilities, one in each hemisphere. Searching for the right frequencies. The best candidates weren’t able to be verified. And yet—8 of the 11 are in the plane of the Milky way. If all of those *are* signals, we can extrapolate the number of transmitting civilizations in the galaxy: about a million. Or perhaps none of them are. That would set limits on different possibilities.
  • In 1992 NASA turned on its own SETI program, from the Mojave Desert, and Arecibo. But Congress defunded it a year later. See testimony, p363. No cost benefits. Some scientists are still working it, anyway.

Ch21, To the Sky!

  • (The chapter title is a line from the Hymn for a Dead Pharaoh, from Egypt circa 2600 bce, used in Philip Glass’s Akhnaten.)
  • Tsiolkovsky, Goddard, later von Braun. And even later, we’ve used the rockets to go into space.
  • This is one reason “now” is so special – see list 370. Now is special because of the many ways we’ve discovered we can destroy ourselves. Such advances may happen on many worlds, and maybe many of those civilizations don’t survive. Considering the Copernican principle of mediocrity, this implies our species is not to last long, 372. No more than 8 million years, Gott says, with a lower limit of 12 years. Those who have been around are likely to stay around; newcomers tend to disappear. At the same time, we’ve developed the means of surviving off the Earth. And nothing means we can’t keep trying to keep our planet habitable, though it may be too difficult for us, 374m.
  • If humanity can spread to other worlds, our species would be insulated from catastrophe. (ref to previous bk, 375 ft) And it would be relatively inexpensive to do so. Author remains a human chauvinist. This is a key missing argument for the expansion of humanity into space.

Ch22, Tiptoeing Through the Milky Way

  • We beware pride, recalling the Tower of Babel, Psalm 15, Plato. Perhaps we need new myths. About how humans need to *become* gods. There’s even a story in the Jewish Talmud about God telling Adam and Eve that it’s their job to ‘complete’ Creation, p382.
  • Both Goddard and Tsiolkovsky made similar judgments. [[ Can we take Wolfe’s New Sun series as aligning with this? Will investigate ]]
  • But perhaps our science and tech are tools too hot to handle. Maybe we should retreat to a simpler society. And yet envy and competition will never go away. Do we make elites control things? Then perhaps a hunger-gatherer society. But that can support only a few millions. Where does everyone else go? We have become powerful without becoming wise. Diversity on many planets would sidestep some of these issues. Mention of the ‘end of history’ 385t. Advancing into space would be a beginning.
  • Other implications:
    • There will be threats from comets, from nearby supernovas, from the sun itself in the long run. So we’ll need to leave the solar system, eventually. Then why haven’t others been seen? Perhaps simply because the stars are so far away, and there wouldn’t be a lot of them.
    • Humanity may split into separate communities, losing contact with each other. They might ‘homestead’ one world (in the Oort Cloud) after the next. Wanderers, as we once were. Perhaps eventually to planets of other suns. Or better to stay hidden in the dark?
    • We will come across new phenomena. The focus of the sun would amplify distant radio signals, and images. Second, brown dwarfs, with habitable worlds. Third, nearby black holes could provide amazing energy.
    • We may eventually spread through the Milky Way. And meet other intelligences. in the coming decades we will explore other stellar systems. Eventually we will be able to reach near the speed of light. It will necessitate increased wisdom to do so before we destroy ourselves. Those who reach the stars will be a species like us, but better, 398t.
    • Over immense timescales galaxies explode. We see quasars, etc, and a halo of dark matter around the Milky Way, containing perhaps planets untethered to stars. We might planet hop to distant galaxies. We’ll likely never explore much of the Milky Way; there’s too much of it. Perhaps we will find goals than merely populating other worlds. To prevent the expansion of the universe; to complete creation.
  • Now return to our own age. How we’ve changed over billions of years since our ancestors. We need a telos, a goal, keeping our frailty and fallibility in mind. But here’s the goal: the survival of the species. Religion is a “feeling of being at home in the Universe” said William James. If we mean the real universe, then we have no true religion yet. The Cosmos is forever; after a sedentary hiatus, we resume our nomadic says. Our descendants will look back toward that blue dot.


One quote, from page 52.5. This was later partially quoted by Richard Dawkins in his Unweaving the Rainbow (1998), as reviewed here.

How is it that hardly any major religion has looked at science and concluded, ‘This is better than we thought! The universe is much bigger than our prophets said, grander, more subtle, more elegant? God must be even greater than we dreamed’? Instead they say, ‘No, no, no! My god is a little god, and I want him to stay that way.’ A religion, old or new, that stressed the magnificence of the Universe as revealed by modern science might be able to draw forth reserves of reverence and awe hardly tapped by the conventional faiths. Sooner or later, such a religion will emerge.

This entry was posted in Book Notes, Science. Bookmark the permalink.

Leave a Reply

Your email address will not be published.