Astronomy: The Pale Blue Dot

            by CORSTEN • April 20th, 2012

Today’s entry is a grounding experience about how inconceivably large and empty space is; That how the planet under our feet, perhaps the largest thing many of us can barely comprehend the scale of, is truly miniscule in the context of the solar system.

Space is big. You just won’t believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space.”
– Douglas Adams

Our story is told by Voyager 1 spacecraft’s unexpected, extra task. Voyager 1 was launched in 1977 and would execute a flyby of Jupiter and Saturn in 1979/1980 respectively, but that is something for another time. This is a story which begins when the primary mission of Voyager 1 had ended.

Once beyond Saturn, the primary mission was complete. The vessel was designed to function this long; any time beyond was bonus and with ever-increasing chance of the inevitable end. To get to Saturn, Voyager 1 was slung through the gravity well of Jupiter, adding to the initial velocity from the inner system approach. The craft did not cease after Saturn: Momentum conserved, with the mild decelleration from the gravity of the sun, the Voyager 1 spacecraft was bound for interstellar space travelling at over sixty thousand kilometers per hour.

Carl Sagan, of Cosmos fame and participant in the Voyager program, proposed a last photographic mission for Voyager on its way out of the system: Turn the craft around and take a photographs of the planets from a distance. There was concern however that to take the photograph immediately would risk destroying the camera, exposing it to the direct rays of the sun from such proximity. It was resolved that in a few years time, once both Voyager craft were beyond the orbit of Pluto, and if luck held out that the crafts were functioning, the photograph would be taken.

In 1989, at the absolute limit of the Voyager program, the time arrived. Six billion kilometers from home, the Voyager 1 craft captured its final images and transmitted them to Earth. The signals to and from Voyager, travelling at the speed of light, would take over 5 hours each way to traverse this distance. In 1990 the data was reassembled and the images complete.

The Earth is the small speck of light blue, on the right side of the image. The shaft of light is one of the many optical flares from the glare of the sun striking the camera. The Voyager craft was much, much too far from the Earth to make out anything greater than this pixel of light… but that was precisely what Carl wanted.

With the data in hand, Carl proceeded with his opus of popular science; The Pale Blue Dot. A book by this title was released, but the principal message was based on cognizance of the scale of the Earth in the image from beyond the planets.


The following is the core of Carl’s message, including handy Youtube Audio pairing.

From this distant vantage point, the Earth might not seem of any particular interest. But for us, it’s different. Consider again that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every superstar, every supreme leader, every saint and sinner in the history of our species lived there, on a mote of dust, suspended in a sunbeam.

The Earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those generals and emperors, so that, in glory and triumph, they could become the momentary masters of a fraction of a dot. Think of the endless cruelties visited by the inhabitants of one corner of this pixel on the scarcely distinguishable inhabitants of some other corner, how frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds. Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light.

Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves. The Earth is the only world known so far to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment the Earth is where we make our stand.

It has been said that astronomy is a humbling and character building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot: the only home we’ve ever known.”

-Carl Sagan, The Pale Blue Dot

I can’t top that, but I can help hammer the point home. 6 billion kilometers is impossible to grasp, so let’s try some thought experiments to help us understand just the relative dimensions in play.


The Voyager craft continue their journeys out of the solar system. Their journey into and beyond the true limit of the solar system, the heliosheath, is perhaps a subject of a future entry. Most of the systems are shut down, but a few critical items remain powered by the plutonium reactors, expected to survive another decade or so. You can view their progress at the link below; At the time of this article, and about this same time each year, the earth is actually getting *closer* to the Voyager spacecraft. How is this possible? The earth’s orbit velocity is greater than the velocity of the Voyager craft, so when we’re both heading the same direction, we’re catching up (briefly! We still orbit the sun; Voyager is gone for good)

Wrapping our head around the magnitude of these scales is challenging, but progress towards this is essential; We’re just scratching the surface. On the astronomical scales of the stars and galaxies, the solar system is just as comparable to the grain of salt.

Pale Blue Dot and Voyager imagery courtesy of NASA free use policy

Further Information:
The Voyager spacecraft are still out there, flying beyond the solar system towards interstellar space. You can see their progress here.

The Family photograph, collage by the Voyager spacecraft

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