The Privileged Planet

How Our Place in the Cosmos Is Designed for Discovery

Guillermo Gonzalez, Jay W. Richards

• Publisher: Regnery
• Year: 2004
• ISBN:
  9781596987074
• Topic: Physical Sciences
• Subtopic: Cosmology

Earth. The Final Frontier Contrary to popular belief, Earth is not an insignificant blip on the universe's radar. Our world proves anything but average in Guillermo Gonzalez and Jay W. Richards' The Privileged Planet: How Our Place in the Cosmos Is Designed for Discovery.But what exactly does Earth bring to the table? How does it prove its worth among numerous planets and constellations in the vastness of the Milky Way? In The Privileged Planet, you'll learn about the world's: life-sustaining capabilities
water and its miraculous makeup
protection by the planetary giantsAnd how our planet came into existence in the first place.

SECTION 1

OUR LOCAL ENVIRONMENT

CHAPTER 1

WONDERFUL ECLIPSES

Perhaps that was the necessary condition of planetary life: Your Sun must fit your Moon.

—Martin Amis¹

INSPIRED

October 24, 1995: the date I had long awaited.* I awoke at 5 A.M., along with several other astronomers in our group. It was a cool, clear morning in Neem Ka Thana, a small town in the dry region of Rajasthan, India, a great place for an eclipse. By 6 A.M. I had staked my claim within a roped-off compound in a local schoolyard and was setting up my scientific instruments. Half a dozen other experimental setups were scattered around me in the compound, each with its own team of astronomers. Some had mounted their experiments on stable concrete piers built weeks before. Around the compound were TV and radio news crews and hundreds of curious onlookers, staring at us as if we were rare zoo exhibits. I had joined the expedition at the invitation of the Indian Institute of Astrophysics in Bangalore. Although the eclipse was not the main purpose of my trip to India, I couldn’t pass up this rare opportunity.

Strictly speaking, like snowflakes, no two solar eclipses are exactly alike, but astronomers sort these events into three types: partial, annular, and total. In a partial eclipse, the Moon fails to completely cover the Sun’s bright photosphere.² In an annular eclipse, although their centers may pass very close to each other, the Moon’s disk is too small to cover the Sun’s photosphere. To qualify as a total eclipse, the Moon’s disk must completely cover the bright solar disk as seen from Earth’s surface. These are the eclipses everyone wants to see. Observers far from the eclipse “centerline” see only a partial eclipse. Only total and very close annular eclipses noticeably darken the sky, while only total eclipses allow us to view the eerie pink chromosphere and silvery-white corona. Under such conditions, the chromosphere looks like a fragile, jagged crown, with pink flames protruding around it like a ring of fire. The corona is the outermost part of the Sun’s atmosphere, extending several degrees farther out from the chromosphere.

Figure 1.1: A total solar eclipse (above) compared to an annular eclipse (below). In a total eclipse, viewers within the Moon’s umbra will see the Moon block the Sun’s entire photosphere. Those within the penumbra will see a partial eclipse. During an annular eclipse, however, the Moon’s shadow cone converges above Earth’s surface, leaving a bright ring of the Sun’s photosphere visible even for the best-placed viewers. Sizes and separations are not drawn to scale.

I had witnessed a number of partial solar eclipses—including two annular ones in 1984 and 1994—but this was to be my first (and, to date, only) experience of a total solar eclipse. My experiment was simple: to measure the changing atmospheric conditions of temperature, pressure, and humidity, and to photograph the event with my 35 mm camera and a telephoto lens.

It was a complete success. The perfect weather both that day and the previous day allowed me to compare the meteorological changes occurring during the eclipse.³ I managed to shoot thirty frames during the fifty-one seconds of totality, the period when the Moon fully eclipses the Sun. The long coronal streamers were plainly visible to the naked eye. (See Plate 3.) Unfortunately, I was so busy snapping photos that I had only a brief glimpse of the eclipsed Sun with my naked eyes. My best view was through the camera’s viewfinder—a common complaint of eclipse watchers.

To experience a total solar eclipse is much more than simply to see it. The event summons all the senses. The dramatic drop in temperature was just as much a part of it as the blocked Sun and the “oohs” and “aahs” from the crowd. Just after the total phase ended, many burst into spontaneous applause, as if rewarding a choreographer for a well-executed ballet.

This was only the fourth total solar eclipse visible from India in the twentieth century. Still, I was surprised at the Indians’ interest in this eclipse. National television covered the event, with crews set up at three or four locations spread across the eclipse path. One of them shared our site. Prior to departing India, I received a videotaped copy of the TV coverage from a colleague. A number of scholars were interviewed on the scientific aspects of solar eclipses; others discussed Indian eclipse mythology and superstitions. The TV producers, it seemed, were trying to show the world that India had finally discarded religious superstition and entered the era of scientific enlightenment. But the widespread superstitious practices in evidence during this eclipse, such as people—especially pregnant women—remaining indoors, suggest they were not quite successful.

Finally, there were the amateur astronomers and eclipse chasers, people who try to see as many total solar eclipses as they can fit into a lifetime. Eclipse chaser Serge Brunier explains in his book Glorious Eclipses: Their Past, Present, and Future, what drives them:

Passionately interested in astronomy ever since the age of twelve, for me eclipses remained, for a long time, simple dates in the ephemerides, and I had to wait until I was thirty-three before witnessing, for professional reasons, my first total eclipse, that of 11 July 1991, from the Hawaiian Observatory on top of Mauna Kea volcano.

It would be an understatement to say that I immediately became passionate about celestial events, which I have followed ever since, over the course of the years and the lunations, more or less all over the planet. Each time, there is the same astonishment and, each time, the feeling has grown that eclipses are not just astronomical events, that they are more than that, and that the emotion, the real internal upheaval, that they produce—a mixture of respect and also empathy with nature—far exceeds the purely aesthetic shock to one’s system.⁴

Brunier describes his first total solar eclipse experience:

The sight is so staggering, so ethereal, and so enchanting that tears come to everyone’s eyes. It is not really night. A soft twilight bathes the Mauna Kea volcano. Along the ridge, the silvery domes, like ghostly silhouettes of a temple to the heavens, stand rigidly beneath the Moon. The solar corona, which spreads its diaphanous silken veil around the dark pit that is the Moon, glows with an other-worldly light. It is a perfect moment.⁵

Amateur astronomers who have traveled abroad to watch solar eclipses have told me that responses are always the same. The locals and the visiting astronomers are equally in awe and often in tears. Being able to predict the circumstances of total solar eclipses to within a second of time anywhere on Earth has not quenched our deepest emotional responses to them; neither has it stopped a modern astronomer like Brunier from describing this most physical of phenomena as ethereal, as spiritual. Is there something more to total solar eclipses than just the mechanics of the Earth-Moon-Sun system? Is there some deep connection, perhaps, between observing them and conscious life on Earth? We believe there is.

THE PHYSICS OF THE MOON

First, consider a little-known fact: A large moon stabilizes the rotation axis of its host planet, yielding a more stable, life-friendly climate. Our Moon keeps Earth’s axial tilt, or obliquity—the angle between its rotation axis and an imaginary axis perpendicular to the plane in which it orbits the Sun—from varying over a large range.⁶ A larger tilt would cause larger climate fluctuations.⁷ At present, Earth tilts 23.5 degrees, and it varies from 22.1 to 24.5 degrees over several thousand years. To stabilize effectively, the Moon’s mass must be a substantial fraction of Earth’s mass. Small bodies like the two potato-shaped moons of Mars, Phobos and Deimos, won’t suffice. If our Moon were as small as these Martian moons, Earth’s tilt would vary not 3 degrees but more than 30 degrees. That might not sound like anything to fuss over, but tell that to someone trying to survive on an Earth with a 60-degree tilt. When the North Pole was leaning sunward through the middle of the summer half of the year, most of the Northern Hemisphere would experience months of perpetually scorching daylight. High northern latitudes would be subjected to searing heat, hot enough to make Death Valley in July feel like a shady spring picnic. Any survivors would suffer viciously cold months of perpetual night during the other half of the year.

Figure 1.2: Earth’s axis currently tilts 23.5 degrees from a line perpendicular to the plane formed by the Earth’s orbit around the Sun, and varies a modest 2.5 degrees over thousands of years. Such stability is due to the action of the Moon’s gravity on Earth. Without a large Moon, Earth’s tilt could vary by 30 degrees or more, even 60 degrees, which would make Earth less habitable.

But it’s not just a large axial tilt that causes problems for life. On Earth, a small tilt might lead to very mild seasons, but it would also prevent the wide distribution of rain so hospitable to surface life. With a 23.5-degree axial tilt, Earth’s wind patterns change throughout the year, bringing seasonal monsoons to areas that would otherwise remain parched. Because of this, most regions receive at least some rain. A planet with little or no tilt would probably have large swaths of arid land.

The Moon also assists life by raising Earth’s ocean tides. The tides mix nutrients from the land with the oceans, creating the fecund intertidal zone, where the land is periodically immersed in seawater. (Without the Moon, Earth’s tides would be only about one-third as strong; we would experience only the regular solar tides.) Until very recently, oceanographers thought that all the lunar tidal energy was dissipated in the shallow areas of the oceans. It turns out that about one-third of the tidal energy is spent along rugged areas of the deep ocean floor, and this may be a main driver of ocean currents.⁸ These strong ocean currents regulate the climate by circulating enormous amounts of heat.⁹ If Earth lacked such lunar tides, Seattle would look more like northern Siberia than the lush, temperate “Emerald City.”

The Moon’s origin is also an important part of the story of life. At the present time, the most popular scenario for its formation posits a glancing blow to the proto-Earth by a body a few times more massive than Mars.¹⁰ That violent collision may have indirectly aided life. For example, it probably helped form Earth’s iron core by melting the planet and allowing the liquid iron to sink to the center more completely.¹¹ This, in turn, may have been needed to create a strong planetary magnetic field, a protector of life that we’ll discuss later. In addition, had more iron remained in the crust, it would have taken longer for the atmosphere to be oxygenated, since any iron exposed on the surface would consume the free oxygen in the atmosphere. The collision is also believed to have removed some of Earth’s original crust. If it hadn’t, the thick crust might have prevented plate tectonics, still another essential ingredient for a habitable planet. In short, if Earth had no Moon, we wouldn’t be here.¹²

Of course, with eclipses it takes three to tango: a star, a planet, and its moon. As long as they are the right relative sizes and distances apart, a total eclipse can happen with a larger or smaller moon or star. But two factors vary considerably: the life-support potential of the host planet and the usefulness of the eclipse for science. Let’s start with the former.

Habitability varies dramatically, depending on the sizes of a planet and its host star and their separation. There are good reasons to believe that a star similar to the Sun is necessary for complex life.¹³ A more massive star has a shorter lifetime and brightens more rapidly. A less massive star radiates less energy, so a planet must orbit closer in to keep liquid water on its surface. (The band around a star wherein a terrestrial planet must orbit t...