How to Measure the Distance to the Stars

How to Measure the Distance to the Stars

The separation of the planets from one another – forty million kilometers from Earth to Venus at closes approach, six billion kilometers to Pluto – would have stunned those Greeks who were outraged by the contention that the Sun might be as large as the Peloponnesus.

It was natural to think of the solar system as much more compact and local. If I had my finger before my eyes and examine it first with my left and then with my right eye, it seems to move against the distant background. The closer my finger is, the more it seems to move. I can estimate the distances to my finger from the amount of this apparent motion, or parallax. If my eyes were farther apart, my finger would seem to move substantially more.

The longer the baseline from which we make our two observations, the greater the parallax and the better we can measure the distances to remote objects. Bu we live on a moving platform, the Earth, which every six months has progressed from one end of its orbit to the other, a distance of 300, 000, 000 kilometers.

How far would we have to travel from the Sun for it appear as small and as dim as a star? Illustration by Elena

If we look at the same unmoving celestial object six months apart, we should be able to measure very great distances. Aristarchus suspected the stars to be distant suns. He placed the Sun among the fixes stars. The absence of detectable stellar parallax as the Earth moved suggested that the stars were much farther away than the Sun. Before the invention of the telescope, the parallax of even the nearest stars was too small to detect. Not until the nineteenth century was the parallax of a star first measured. It then became clear, from straightforward Greek geometry, that the stars were light-years away.

There is another way to measure the distance to the stars which the Ionians were fully capable of discovering, although, so far as we know, they did not employ it. Everyone knows that the farther away an object is, the smaller it seems. This inverse proportionality between apparent size and distance is the basis of perspective in art and photography. So the farther away we are from the Sun, the smaller and dimmer it appears. How far would we have to be from the Sun for to appear as small and as dim as a star? Or, equivalently, how small a piece of the Sun would be as bright as a star?

An early experiment to answer this question was performed by Christian Huygens, very much in the Ionian tradition. He drilled small holes in a brass plate, held the plate up to the Sun and asked himself which hole seemed as bright as he remembered the bright star Sirius to have been the night before. The hole was effectively 1/28,000 the apparent size of the Sun (Huygens actually used a glass bead to reduce the amount of light passed by the hole). So Sirius, he reasoned, must be 28,000 times farther from us than the Sun, or about half a light-year away. It is hard to remember just how bright a star is many hours after you look at it, but Huygens remembered very well. If he had known that Sirius was intrinsically brighter than the Sun, he would have come up with almost exactly the right answer: Sirius is 8,8 light-years away. The fact that Aristarchus and Huygens used imprecise data and derived imperfect answers hardly matters. They explained their methods so clearly that, when better observations were available, more accurate answers could be derived.

Intelligent Life in the Universe

Intelligent Life In the Universe

We have launched four ships to the stars, Pioneer 10, Pioneer 11, Voyager 1 and Voyager 2. They are primitive and backward craft, moving, compared to the immense interstellar distances, with a slowness of a race in a dream.

In the future we will do better.. Our ships will travel faster. There will be designated interstellar objectives, and sooner or later our spacecraft will have human crews.

In the Milky Way Galaxy there must be many planets millions of years older than Earth, and some that are billions of years older. Should we not have been visited? In all the billions of years since the origin of our planet, has there not been even once a strange craft from a distant civilization surveying our world from above, and slowly settling down to the surface to be observed by iridescent dragonflies, incurious reptiles, screeching primates or wondering humans?

I wish it were otherwise. There is something irresistible about a discovery of even a token, perhaps a complex inscription, but best by far, a key to the understanding of an alien and exotic civilization. It is an appeal we humans have felt before. Image : © Elena

The idea is natural enough. It has occurred to everyone who has contemplated, even casually, the question of intelligent life in the universe. But has it happened if fact? The critical issue is the quality of purported evidence, rigorously and sceptically scrutinized – not what sounds plausible, not the unsubstantiated testimony of one or two self-professed eyewitnesses.

By this standard there are no compelling cases of extraterrestrial visitation, despite all the claims about UFOs and ancient astronauts which sometimes makes it seem that our planet is awash in uninvited guests.

Our Sisters and Brothers

On some planets, intelligent life may have evolved, reworking the planetary surface in some massive engineering enterprise. These are our sisters and brothers in the Cosmos.

Are these creatures very different from us? What is their biochemistry, their form, neurobiology, history, science, religion, politics, technology, art, music, philosophy? Do they have long haired ears? Is their sky blue and their soil red? Perhaps some day we will know them.

How do these creatures look? Photo : © Elena

There must be many worlds scattered through space, but our search for them just begins now, with the accumulated wisdom of the men and women of our species, garnered at great cost over a million years.

And finally, at the end of all our wanderings, we return to our tiny, fragile, blue-white world, lost in a cosmic ocean vat beyond our most courageous imagining. Our world is a world among an immensity of others. It may be significant only for us. Or it may be the center of the Universe.

Tycho and Kepler

Tycho and Kepler

Tycho Brahe

A provincial schoolteacher of humble origins, unknown to all but a few mathematicians, Johannes Kepler was diffident about Tycho’s offer to join him in Prague. But the decision was made for him. In 1598, one of the many premonitory tremors of the coming Thirty Years’ Was engulfed him. The local Catholic archduke, steadfast in dogmatic certainty, vowed he would rather “make a desert of the country than rule other heretics” (By no means the most extreme such remark in medieval or Reformation Europe. Upon being asked how to distinguish the faithful from the infidel in the siege of a largely Albigensian city, Domingo de Guzman, later known as Saint Dominic, allegedly replied: “Kill the all. God will know his own”.) Protestants were excluded from economic and political power. Kepler’s school was closed, and prayers, books and hymns deemed heretical were forbidden. Finally the townspeople were summoned to individual examinations on the soundness of their private religious convictions, those refusing to profess the Roman Catholic faith being fined a tenth of their income and, upon pain of death, exiled forever from Graz. Kepler chose exile: “Hypocrisy I have never learned. I am in earnest about faith. I do not play with it”.

Dynascope RV-6. “Hypocrisy I have never learned. I am in earnest about faith. I do not play with it” (Johannes Kepler). Image: In public domain.

Leaving Graz, Kepler, his wife and stepdaughter set out on the difficult journey to Prague. Theirs was not a happy marriage. Chronically ill, having recently lost two young children, his wife was described as “stupid, sulking, lonely, melancholy”. She had no understanding of her husband’s work and, having been raised among the minor rural gentry, she despised his impecunious profession. He for his part alternately admonished and ignored her, “for my studies sometimes made me thoughtless; but I learned my lesson, I learned to have patience with her. When I saw that she took my words to heart, I would rather have bitten by own finger to give her further offense”. But Kepler remained preoccupied with his work.

He aspired to become a colleague of the great Tycho Brahe, who for thirty-five years had devoted himself, before the invention of the telescope, to the measurement of a clockwork universe, ordered and precise. Kepler’s expectations were to be unfulfilled. Tycho himself was a flamboyant figure, festooned with a golden nose, the original having been lost in a student duel fought over who was the superior mathematician. Around him was a raucous entourage of assistants, sycophants, distant relatives and assorted hangers-on. Their endless revelry, their innuendoes and intrigues, their cruel mockery of the pious and scholarly country bumpkin depressed and saddened Kepler : “Tycho… is superlatively rich but knows not how to make use of it. Any single instrument of his costs more than my and my whole family’s fortunes put together”.

Johannes Kepler

Impatient to see Tycho Brahe’s astronomical data, Johannes Kepler would be thrown only a few scraps at a time: “Tycho gave me no opportunity to share in his experiences. He would only, in the course of a meal and, in between other matters, mention, as if in passing, today the figure of the apogee of one planet, tomorrow the nodes of another… Tycho possesses the best observations… He also has collaborators. He lacks only the architect who would put it all this to use. » Tycho was the greatest observational genius of the age, and Kepler the greatest theoretician.

Each knew that, alone, he would be unable to achieve the synthesis of an accurate and coherent world system, which they both felt to be imminent. But Tycho was not about to make a gift of his life’s work to a much younger potential rival. Joint authorship of the results, if any, of the collaboration was for some reason unacceptable.

The birth of modern science – the offspring of theory and observation – teetered on the precipice of their mutual mistrust. In the remaining eighteen months that Tycho was to live, the two quarreled and were reconciled repeatedly.

Let me not seem to have lived in vain. Image: A Flashing Texture by © Megan Jorgensen (Elena)

At a dinner given by the Baron of Rosenberg, Tycho, having robustly drunk much wine, “placed civility ahead of health”, and resisted his body’s urging to leave, even if briefly, before the baron. The consequently urinary infection worsened when Tycho resolutely rejected advice to temper his eating and drinking. On his deathbed, Tycho Brahe bequeathed his observations to Kepler, and “on the last night of his gentle delirium, he repeated over and over again these words, like someone composing a poem: “Let me not seem to have lived in vain… Let me not seem to have lived in vain…”

After Tycho Brahe’s death, Johannes Kepler, now the new Imperial mathematician, managed to extract the observations from Tycho’s recalcitrant family. His conjecture that the orbits of the planets are circumscribed by the five platonic solids were no more supported by Tycho’s data than by Copernicus’.

Tycho’s observation of the apparent motion of Mars and other planets through the constellations were made over a period of many years. These data, from the last few decades before the telescope was invented, were the most accurate that yet had been obtained. Kepler worked with passionate intensity to understand them. What real motion of the Earth and Mars about the Sun could explain, to the precision of measurement, the apparent motion of Mars in the sky, including its retrograde loops through the background constellations.

Immanuel Velikovsky

Immanuel Velikovsky

As we have discussed at some length elsewhere, the ideas of Immnuel Velikovsky are almost certainly wrong. Astronomers do not object to the idea of major collisions in space, only to major recent collisions. In any model of the solar system it is impossible to show the sizes of the planets on the same scale as their orbits, because the planets would then be almost too small to see.

If the planets were really shown to scale, as grains of dust, we would easily note that the chance of collision of a particular comet with the Earth in a few thousand years is extraordinarily low. Moreover, Venus is a rocky and metallic, hydrogen-poor planet, whereas Jupiter – where Velikovsky supposed it comes from – is made almost entirely of hydrogen. There are no energy sources for comets or planets to be ejected by Jupiter.

If one passed by the Earth, it could not “stop” the Earth’s rotation, much less start it up again at twenty-four hours a day. No geological evidence supports the idea of an unusual frequency of vulcanism or floods 3,500 years ago. There are Mesopotamian inscriptions referring to Venus that predate the time when Velikovsky says Venus changed from a comet into a planet: The Adda cylinder seal, dating from the middle of the third millennium B.C., prominently displays Inanna, the goddess of Venus, the morning star, and precursor of the Babylonian Istar.

The suppression of uncomfortable ideas may be common in religion and politics, but it is not the path to knowledge. Image : Alien Illusion © Megan Jorgensen (Elena)

It is very unlikely that an object in such a highly elliptical orbit could be rapidly moved into the nearly perfect circular orbit of present-day Venus… And so on.

In fact, many hypotheses proposed by scientists as well as by non-scientists turn out to be wrong. But science is a self-correcting enterprise. To be accepted, all ideas must survive rigorous standards of evidence. The worst aspect of the Velikovsky affair is not that his hypotheses were wrong or in contradiction to firmly established facts, but that some who called themselves scientists attempted to suppress Velikovsky’s work. Science is generated by and devoted to free inquiry: the idea that any hypothesis, no matter how strange, deserves to be considered on its merits.

The suppression of uncomfortable ideas may be common in religion and politics, but it is not the path to knowledge; it has no place in the endeavour of science. We do not know in advance who will discover fundament new insights.

After Landing on Mars

After Landing on Mars

For Viking 1, the original landing site seemed, after the scientists examined orbiter photographs and late-breaking Earth-based radar data, unacceptably risky. For a while Carl Sagan was worried that Viking 1 had been condemned, like the legendary Flying Dutchman, to wander the skies of Mars forever, never to find safe heaven. Eventually the scientists found a suitable spot, still in Chryse but far from the confluence of the four ancient channels. The delay prevented them from setting down on July 4, 1976, but it was generally agreed that a crash landing on that date would have been an unsatisfactory two hundredth birthday present for the United States. The scientists deboosted from orbit and entered the Martian atmosphere sixteen days later.

After an interplanetary voyage of a year and a half, covering a hundred million kilometers the long way round the Sun, each orbiter/lander combination was inserted into its proper orbit about Mars; the orbiters surveyed candidate landing sites; the landers entered the Martian atmosphere on radio command and correctly oriented ablation shield, deployed parachutes, divested coverings, and fired retro-rockets. In Chryse and Utopia, for the first time in human history, spacecraft had touched down, gently and safely, on the red planet. These triumphant landings were due to considerable part to the great skill invested in their design, fabrication and testing, and to the abilities of the spacecraft controllers. But for so dangerous and mysterious a planet as Mars, there was also at least an element of luck.

One way or another, Mars is a world to which we will return. Image : The End by © Megan Jorgensen (Elena)

Immediately after landing, the first pictures were to be returned. The scientists knew thay had chosen dull places. But they could hope. The first picture taken by the Viking 1 lander was of one of its own footpads – in case it were to sink into Martian quicksand, the humans wanted to know about it before the spacecraft disappeared. The picture built up, line by line, until with enormous relief the scientists saw the footpad sitting high and dry above the Martian surface. Soon other pictures came into being, each picture element radioed individually back to Earth.

Carl Sagan remembered being transfixed by the first lander image to show the horizon of Mars. This was not an alien world, he thought. He knew places like it in Colorado and Arizona and Nevada. There were rocks and sand drifts and a distant eminence, as natural and unselfconscious as any landscape of Earth. Mars was a place. Sagan would, of course, have been surprised to see a grizzled prospector emerge from behind a dune leading his mule, but at the same time the idea seemed appropriate. Nothing remotely like it ever entered his mind in all the hours he spent examining the Venera 9 and 10 images of the Venus surface.

Landing On Mars

The combination of Soviet successes of landing on Venus and Soviet failures on landing on Mars naturally caused some concern about the US Viking mission, which had been informally scheduled to set one of its two descent craft gently down on the Martian surface on the Bicentennial of the United States, July 4, 1976.

Like its Soviet predecessor, the Viking landing maneuver involved an ablation shield, a parachute and retro-rockets. Because the Martian atmosphere is only 1 percent as dense as the Earth’s, a very large parachute, eighteen meters in diameter, was deployed to slow the spacecraft as it entered the thin air of Mars. The atmosphere is so thin that if Viking had landed at a high elevation there would not have been enough atmosphere to brake the descent adequately: it would have crashed. One requirement, therefore, was for a landing site in a low-lying region. From Mariner 9 results and ground-based radar studies, we knew many such areas.

To avoid the probable fate of Mars 3, the Americans wanted Viking to land in a place and time at which the winds were low. Winds that would make the lander crash were probably strong enough to lift dust off the surface. If the scientists could check that the candidate landing site was not covered with sifting, drifting dust, they would have at least a fair chance of guaranteeing that the winds were not intolerably high. This was one reason that each Viking lander was carried into Mars orbit with its orbiter, and descent delayed until the orbiter surveyed the landing site. They had discovered with Mariner 9 that characteristic changes in the bright and dark patterns on the Martian surface occur during times of high winds. The scientists certainly would not have certified a Viking landing site as safe if orbital photographs had shown such shifting patterns.

Nobody wishes to land in too rough a place (Quotations from Megan Jorgensen). Image by Meg Jorgensen  (Elena) A Wallflower

But the guaranties could not be 100 percent reliable. For example, the American scientists could imagine a landing site at which the winds were so strong that all mobile dust had already been blown away. The scientists would then have had no indication of the high winds that might have been there. Detailed weather predictions for Mars were, of course, much less reliable than for Earth. (Indeed one of the many objectives of the Viking mission was to improve the understanding of the weather on both planets).

Because of communication and temperature constraints, Viking could not land at high Martian latitudes. Farther poleward than about 45 or 50 degrees in both hemispheres, either the time of useful communication of the spacecraft with the Earth or the period during which the spacecraft would avoid dangerously low temperatures would have been awkwardly short.

Life on Mars

The Mars landscape is stark and red and lovely: boulders thrown out in the creation of a crater somewhere over the horizon, small sand dunes, rocks that have been repeatedly covered and uncovered by drifting dust, plumes of fine-grained material blown about by the winds. Where did the rocks come from? How much sand had been blown by wind? What must the previous history of the planet have been to create sheared rocks, buried boulders, polygonal gouges in the ground? What are the rocks made of? The same materials as the sand? Is the sand merely pulverized rock or something else? Why is the sky pink? What is the are made of? How fast does the wind blow? Are there marsquakes? How do the atmospheric pressure and the appearance of the landscape change with the seasons?

For every one of these questions Viking has provided definitive or at least plausible answers. The Mars revealed by the Viking mission is of enormous interest – particularly when we remember that the landing sites were chosen for their dullness. But the cameras revealed no sign of canal builders, no Barsoomian aircars or short sword, no princesses or fighting men, no thoats, no footprints, not even a cactus or a kangaroo rat. For as far as we could see, there was not a sign of life.

Viking Orbits Mars. To look for life on Mars, we must look for microbes.Image in public domain, by NASA.

(There was a brief flurry when the Uppercase letter B, a putative Martian graffito, seemed to be visible on a small boulder in Chryse. But later analysis showed it to be a trick of light and shadow and the human talent for pattern recognition. It also seems remarkable that the Martians should have tumbled independently to the Latin alphabet. But there was just a moment when resounding in Sagan’s head was the distant echo of a word from his boyhood – Barsoom).

Perhaps there are large life-forms on Mars, but not in the two first landing sites. Perhaps there are smaller forms in every rock and sand grain. For most of its history, those regions of the Earth not covered by water looked rather like Mars today – with an atmosphere rich in carbon dioxide, with ultraviolet light shining fiercely down on the surface through an atmosphere devoid of ozone. Large plants and animals did not colonize the land until the last 10 percent of Earth history. And yet for three billion years there were microorganisms everywhere on Earth.

Absence of Life

Very little effort was made to calibrate the experiments with plausible inorganic Martian surface materials. Mars is not the Earth. As the legacy of Percival Lowell, who saw canals on Mars, reminds us, we can be fooled. Perhaps there is an exotic inorganic chemistry in the Martian soil that is able by itself, in the absence of Martian microbes, to oxidize foodstuffs. Perhaps there is some special inorganic, nonliving catalyst in the soil that is able to fix atmospheric gases and convert them into organic molecules.

Recent experiments suggest that this may indeed be the case. In the great Martian dust storm of 1971, spectral features of the dust were obtained by the Mariner 9 infrared spectrometer. In analyzing theses spectra, O.B. Toon, J. B. Pollack and Carl Sagan found that certain features seem best accounted for by montoillonite and other kinds of clay, Subsequent observations by the Viking lander support the identification of windblown clays on Mars. Now, A. Banin and J. Rishpon have found that they can reproduce some of the key features – those resembling photosynthesis as well as those resembling respiration – of the “successful” Viking microbiology experiments if in laboratory experiments they substitute such clays for the Martian soil. The clays have a complex active surface, given too adsorbing and releasing gases and to catalyzing chemical reactions. It is too soon to say that all the Viking microbiology results can be explained by inorganic chemistry, but such a result would no longer be surprising. The clay hypothesis hardly excludes life on Mars, but it certainly carries us far enough to say that there is no compelling evidence for microbiology on Mars.

Mars is not the Earth, don’t be fooled! People there may don’t be what they look. Image: © Sketch Drawing Megan Jorgensen (Elena)

Even so, the results of Banin and Rishpon are of great biological importance because they show that in the absence of life there can be a kind of soil chemistry that does some of the same things life does. On the Earth before life, there may already have been chemical processes resembling respiration and photosynthesis cycling in the soil, perhaps to be incorporated by life once it arose. In addition, we know that montorillonite clays are a potent catalyst for combining amino acids into longer chain molecules resembling proteins. The clays of the primitive Earth may have been the forge of life, and the chemistry of contemporary Mars may provide essential clues to the origin and early history of life on our planet.