Spectrum of Light

Spectrum of Light

The spectrum runs from high frequencies of visible light to low ones – violet, blue, green, yellow, orange and red (light is a wave motion; its frequency is the number of wave crests, say, entering a detection instrument, such as a retina, in a given unite of time, such as a second. The higher the frequency the more energetic the radiation).

Since we see these colors, it is called the spectrum of visible light. But there is far more light than the small segment of the spectrum we can see. At higher frequencies, beyond the violet, is a part of the spectrum called the ultraviolet: a perfectly real kind of light, carrying death to the microbes. It is invisible to us, but readily detectable by bumblebees and photoelectric cells. There is much more to the world than we can see. Beyond the ultraviolet is the X-ray part of the spectrum, and beyond the X-rays are the gamma rays. At lower frequencies, on the other side of red, is the infrared part of the spectrum. It was first discovered by placing a sensitive thermometer In what to our eyes is the dark beyond the red. The temperature rose. There was light falling on the thermometer even though it was invisible to our eyes. Rattlesnakes and doped semiconductors detect infrared region of the radio waves. From gamma rays to radio waves, all are equally respectable brands of light. All are useful in astronomy. But because of the limitations of our eyes, we have a prejudice, a bias, toward that tiny rainbow band we call the spectrum of visible light.

Pusha, the cat. Photo by Elena

In 1844, the philosopher Auguste Comte was searching for an example of a sort of knowledge that would be always hidden. He chose the composition of distant stars and planets. We would never physically visit them, he thought, and with no sample in hand it seemed we would forever be denied knowledge of their composition. But only three years after Comte’s death, it was discovered that a spectrum can be used to determine the chemistry of distant objects. Different molecules and chemical elements absorb different frequencies or colors of light, sometimes in the visible and sometimes elsewhere in the spectrum. In the spectrum of a planetary atmosphere, a single dark line represents an image of the slit in which light is missing, the absorption of sunlight during its brief passage through the air of another world. Each such line is made by a particular kind of molecule or atom. Every substance has its characteristic spectral signature. The gases on Venus can be identified from the Earth, 60 million kilometers away. We can divine the composition of the Sun (in which helium, named after the Greek sun god Helios, was first found); of magnetic A stars rich in europium; of distant galaxies analyzed through the collective light of a hundred billion constituent stars. Astronomical spectroscopy is an almost magical technique. It amazes scientists – the fact that Auguste Comte picked a particularly unfortunate example.

There is much more to the world than we can see. Image Alternate Reality by © Elena

Measurement of the Earth

Measurement of the Earth

One day Eratosthenes read in a papyrus book that in the southern frontier outpost of Syene, near the first cataract of the Nile, at noon of June 21 vertical sticks cast no shadows. Eratosthenes was really amused and went on reading…

On the summer solstice, the longest day of the year, as the hours crept toward midday, the shadows of temple columns grew shorter. At noon, they were gone. A reflection of the Sun could then be seen in the water at the bottom of a deep well. He Sun was directly overhead.

It was an observation that someone else might easily have ignored. Sticks, shadows, reflections in wells, the Sun over the head, what the matter? of what possible importance could such simple everyday observations be?

But Eratosthenes was a scientist, and his musing on these commonplaces changed the world. In a way, they made our world, as Eratosthenes actually had the presence of mind to do an experiment to observe whether in Alexandria vertical sticks cast shadows near noon on June 21. And, he discovered, sticks do cast shadows!

The scientist asked himself how, at the same moment, a stick in Syene could cast no shadow and a stick in Alexandria, far to the North, could cast a pronounced shadow? Consider now a map of ancient Egypt with two vertical sticks of equal length, one stuck in Syene and the other in Alexandria.

On this planet Earth the fear of death follows from the fear of life. A man who lives fully is prepared to die at any time. (Mark Twain). Photo : Elena

Suppose that, at a certain moment, each stick casts no shadow at all. This is perfectly easy to understand – provided the Earth is flat and the Sun would then be directly overhead. But if the two sticks cast shadows of equal length that also would make sense on a flat Earth: the Sun’s rays would then be inclined at the same angle to the two sticks. But how could it be that at the same instant there was no shadow at Syene and a substantial shadow at Alexandria?

The only possible answer, he saw, was that the surface of the Earth is curved. Not only that: the greater the curvature, the greater the difference in the shadow lengths. The Sun is so far away that its rays are parallel when they reach the Earth. Sticks placed at different angles to the Sun’s rays cast shadows of different lengths. For the observed difference in the shadow lengths, the distance between Alexandria and Syene had to be about seven degrees along the surface of the Earth; that is, if you imagine the sticks extending down to the center of the Earth, they would there intersect at an angle of seven degrees. Seven degrees is something like one-fiftieth of three hundred and sixty degrees, the full circumference of the Earth. Eratosthenes knew that the distance between Alexnadria and Syene was approximately 800 kilometers, because he hired a man to pace it out. Eight hundred kilometers 50 is 40,000 kilometers: so that must be the circumference of the Earth.

This is the right answer! Eratosthenes only tools were sticks, eyes, feet and brain, plus a taste for experiment. With them he deduced the circumference of the Earth with an error of only a few percent, a remarkable achievement for 2,200 years ago. He was the first person accurately to measure the size of our planet.

Discovery by Eratosthenes

The discovery that the Earth is a very little world was made, as so many very important human discoveries were, in the ancient Near East, in a time some humans still call the third century B.C. This discovery was made in the greatest metropolis of the age, the Egyptian city of Alexandria.

There lived a man in this city, named Eratosthenes. He was an astronomer, philosopher, poet, theater critic, historian and mathematician. The title of the books he wrote range from Astronomy to On Freedom from Pain.

One of his envious contemporaries called him Beta, the second letter of the Greek alphabet, because, he said, Eratosthenes was second best in the world in anything.

It seems clear that in almost everything Eratosthenes was Alpha. He was also the director of the great library of Alexandria. One day thus he read in a papyrus book that in the southern frontier outpost of Syene, near the first cataract of the Nile, at noon of June 21 vertical sticks cast no shadows. Eratosthenes was really amused and went on reading…

(By Carl Sagan, Cosmos).

The Earth, Illustration by Elena.

Back-contamination

Back-contamination

Any space mission carries with it a novel danger: back-contamination. If we wish on Earth to examine samples of Martian soil for microbes, we must, of course, not sterilize the samples beforehand. The point of the expedition is to bring them back alive. But what then? Might Martian microorganisms returned to Earth pose a public health hazard? The Martians of H. G. Wells and Orson Welles, preoccupied with the suppression of Bournemouth and Jersey City, never noticed until too late that their immunological defenses were unavailing against the microbes of Earth. Is the converse possible? This is a serious and difficult issue. There may be no micromartians. If they exist, perhaps we can eat a kilogram of them with no ill effects. But we are not sure, and the stakes are high.

If we wish to return unsterilized Martian samples to Earth, we must have a containment procedure that is stupefyingly reliable. There are nations that develop and stockpile bacteriological weapons. They seem to have an occasion accident, but they have not yet, so far as we know, produced global pandemics. Perhaps Martian samples can be safely returned to Earth. But we would want to be very sure before considering a returned-sample mission.

Are there ancient river valleys on Mars? Image: Bright Crystall Ball Shining © Elena

There is another way to investigate Mars and the full range of delights and discoveries this heterogeneous planet holds for us. Carl Sagan’s most persistent emotion in working with the Viking lander pictures was frustration of our immobility He found himself unconsciously urgin the spacecraft at least to stand on its tiptoes, as if this laboratory, designed for immobility, were perversely refusing to manage even a little hop. How he longed to poke that dune with the sample arm, look for life beneath that rock, see if that distant ridge was a crater rampart. And not so very far to the southeast, he knew, were the four sinuous channels of Chryse.

For all the tantalizing and provocative character of Viking results, we know a hundred places on Mars which are far more interesting than these landing sites. The ideal tool a roving vehicle carrying on advanced experiments, particularly in imaging, chemistry and biology. Prototypes of such rovers are under development by NASA. They know on their own how to go over rocks, how not to fall down ravines, how to get out of tight spots. It is within our capability to land a rover on Mars that could scan their surroundings, see the most interesting place in the field of view, and, by the same time tomorrow, be there. Every day a new place, a complex, winding traverse over the varied topography of this appealing planet.

Such a mission would reap enormous scientific benefits, even if there is no life on Mars. We could wander down the ancient river valleys, up the slopes of one of the great volcanic mountains, along the strange stepped terrain of the icy polar terraces, or muster a close approach to the beckoning pyramids of Mars (the largest are 3 kilometers across at the base and 1 kilometer high – much larger than the pyramids of Sumer, Egypt or Mexico on Earth. They seem eroded and ancient, and are, perhaps, only small mountains, sandblasted for ages. But they warrant, we think, a careful look).

Public interest in such a mission would be sizable. Every day a new set of vistas would arrive on our home television screens. We could trace the route, ponder the findings, suggest new destinations. The journey would be long, the rover obedient to radio commands from Earth. There would be plenty of time for good new ideas to be incorporated into the mission plan. A billion people could participate in the exploration of another world.

Who Speaks for Earth?

Who Speaks for Earth?

How vast those Orbs must be, and how inconsiderable this Earth, the Theatre upon which all our might Desings, all our Navigations, and all our Wars are transacted, is when compared to them. A very fit consideration, and matter of Reflection, for those Kings and Princes, who sacrifice the Lives of so many People, only to flatter their Ambition in being Masters of some pitiful corner of this small Spot (Christian Huygens, New Conjectures Concerning the Planetary Worlds, Their Inhabitants and Productions, circa 1690).

We look back through countless millions of years and see the great will to live struggling out of the intertidal slime, struggling from shape to shape and from power to power, crawling and the walking confidently upon the land, struggling generation after generation to master the air, creeping down into the darkness of the deep; we see it turn upon itself in rage and hunger and reshape itself anew, we watch it draw nearer and more akin to us, expanding, elaborating itself, pursuing its relentless inconceivable purpose, until at last it reaches us and its being beats through our brains and arteries… It is possible to believe that all the past is but the beginning of a beginning, and that all that is and has been is but the twilight of the dawn.

Life on Earth. Photo by Elena

It is possible to believe that all that the human mind has ever accomplished is but the dream before the awakening…

Out of our lineage, mind will spring, that will reach back to us in our littleness to know us better than we know ourselves. A day will come, one day in the unending succession of days, when being, beings who are now latent in our thoughts and hidden in our loins, shall stand upon this earth as one stands upon a footstool, and shall laugh and reach out their hands amidst the stars.

(Herbert G. Wells, The Discovery of the Future” Nature 65, 326 (1902)

To what purpose should I trouble myself in searching out the secrets of the stars, having death or slavery continually before my eyes? (A question put to Pythogaras by Anaximenes (circe 600 B.C.), according to Montaigne. Image Jaime Murray as H.G.Wells in Warehouse 12 TV series

Heaven for Humans

Heaven for Humans

Might the cooling increase the size of the polar ice cap, which, because it is bright, will reflect still more sunlight from the Earth, further cooling the planet, driving a runaway albedo effect? (The albedo is the fraction of the sunlight striking a planet that is reflected back to space. The albedo of the Earth is some 30 to 35 percent. The rest of the sunlight is absorbed by the ground and is responsible for the average surface temperature).

Our lovely blue planet, the Earth, is the only home we know. Venus is too hot. Mars is too cold. But the Earth is just right, a heaven for humans, After all, we evolved here. But our congenial climate may be unstable. We are perturbing our poor planet in serious and contradictory ways. Is there are any danger of driving the environment of the Earth toward the planetary Hell of Venus or the global ice age of Mars? The simple answer is that nobody knows. The study of the global climate, the comparison of the Earth with other worlds, are subjects in their earliest stages of development. They are fields that are poorly and grudgingly funded. In our ignorance, we continue to push and pull, to pollute the atmosphere and brighten the land, oblivious of the fact that the long-term consequences are largely unknown.

A palm tree on Earth. Photo by Elena.

A few million years ago, when human beings first evolved on Earth, it was already a middle-aged world, 4,6 billion years along from the catastrophes and impetuosities of its youth. But we humans now represent a new and perhaps decisive factor. Our intelligence and our technology have given us the power to affect the climate. How will we use this power? Are we willing to tolerate ignorance and complacency in matters that affect the entire human family? Do we value short-term advantages above the welfare of the Earth? Or will we think on longer time scales, with concern for our children and our grandchildren, to understand and protect the complex life-support systems of our planet?

The Earth is a tiny and fragile world. It needs to be cherished. Image: Palm Tree Sketch Drawing © Elena