The Exceptional Nature of Our Sun
AS YOU read this article, either the sun is up or you know it will rise before long. Is that important? Yes, because without the radiance of the sun, earth’s trillions of living things—including you—would not be here. Gone would be the variety of life distributed among the millions of species, ranging from single-celled bacteria to immense whales.
It is true that only about half a billionth of the sun’s energy output reaches our planet. Yet, even those few “crumbs” from the solar “table” are enough to nourish and sustain life on earth. Not only that, but if this tiny trickle that arrives could be harnessed efficiently, it could easily meet the energy needs of our modern society, with power to spare.
Most astronomy books say that our sun is an ordinary star, “a rather commonplace celestial object.” But is the sun in every respect a “commonplace celestial object”? Guillermo Gonzalez, an astronomer at the University of Washington in Seattle, has suggested that our sun is exceptional. Should this affect the search for life on other planets? Gonzalez answers: “There are fewer stars suitable for intelligent life than people realise.” He adds: “Unless astronomers narrow down their search to stars as exceptional as the Sun, they are wasting much of their time.”
What are some characteristics that make our sun suitable for nurturing life? As we examine these factors, we should keep in mind that many statements on the physics of the universe are theoretical in nature.
● A single star: Astronomers estimate that 85 percent of the stars in the neighborhood of the sun are in groups of two or more stars that orbit one another. Such stars are bound together by gravitational forces.
The sun, however, is a single star. “The case of the sun as a single star seems, then, to be rather unusual,” writes astronomer Kenneth J. H. Phillips in his book Guide to the Sun. That single status of the sun gives the earth a more stable orbit, which, in turn, makes for conditions that contribute to life on this globe, says Gonzalez.
● A massive star: Another related idiosyncrasy of the sun, according to Gonzalez, is that “it is among the most massive 10 percent of stars in its neighbourhood,” reports New Scientist magazine. Phillips notes: “The sun contains 99.87% of the mass of the solar system and as a result gravitationally controls all bodies in the solar system.”
This characteristic allows for the earth to be relatively far from the sun—93 million miles [150 million km]—and still not pull away from it. This comparatively large distance, in turn, protects life on earth from being scorched by the sun.
● Heavy elements: Gonzalez notes that the sun has 50 percent more heavy elements—carbon, nitrogen, oxygen, magnesium, silicon, and iron—than other stars of its age and type. In this, our sun stands out among its peers. “The abundances of heavy elements in the sun are very low,” says Phillips, “but some stars . . . have even lower heavy-element abundances.” In fact, stars that have heavy-element abundances like that of the sun belong to the specific category called Population I stars.
How does this relate to the existence of life on earth? Well, the heavy elements are necessary to support life. But they are rare, making up less than 1 percent of the universe. Our earth, though, consists almost entirely of the heavier elements. Why? Because, astronomers say, the earth orbits such an unusual home star—our sun.
● A less elliptic orbit: Another advantage arises from the sun’s being a Population I star. “Population I stars are generally performing nearly circular orbits round the centre of the galaxy,” says the book Guide to the Sun. The sun’s orbit is less elliptic than that of other stars of its age and type. Why would that affect the existence of life on earth? Because the circularity of the sun’s orbit prevents the sun from plunging into the inner galaxy, which is frequented by supernovas (exploding stars).
● Variation in brightness: Here lies another interesting fact about the star of our solar system. Compared with similar stars, the sun has significantly less variation in brightness. In other words, its luminosity is more stable and constant.
Such a relatively stable output of light is critical for life on earth. “Our very presence on the planet,” says science historian Karl Hufbauer, “is evidence that the sun’s luminosity is one of the more stable environmental factors.”
● Tilt of the orbit: The sun’s orbit is only slightly inclined to the galactic plane of the Milky Way. That means that the angle between the plane of the orbit of the sun and the plane of our galaxy is very small. How does this contribute to the welfare of life on earth?
Far beyond the ends of our solar system, a vast spherical reservoir of comets, called the Oort cloud, surrounds us.* Suppose that the inclination of the sun’s orbit to the galactic plane were greater. Then the sun would abruptly cross the plane of our galaxy, which could stir up the Oort cloud. What would the result be? The earth would be bombarded with a catastrophic rain of comets, say astronomers.
What Can Solar Eclipses Tell Us?
There are at least 60 moons in our solar system. They orbit seven of the system’s nine planets. The earth, however, seems to be the only planet in the solar system that enjoys the spectacle of total eclipses. Why is that?
A solar eclipse occurs when the moon comes between the sun and the earth. To get a perfect overlap, the apparent sizes of the sun and the moon have to be roughly the same, so that the moon almost totally covers the sun. And this is exactly the case! Although the sun is 400 times bigger in diameter than the moon, it is also nearly 400 times farther away from the earth than is the moon.
But the earth’s distance from the sun—and thus the apparent size of the sun—is more than simply a factor in the forming of a total eclipse. It is also a vital condition for the existence of life on earth. “If we were a little nearer or farther from the Sun,” Gonzalez says, “the Earth would be too hot or too cold and so uninhabitable.”
There is more. Earth’s unusually large moon helps life on this planet because its gravitational pull prevents the earth from wobbling around too much on its axis. Such wobbling would cause wild and catastrophic swings in climate. So to have life on earth, what is needed is an exact combination of the right distance between sun and earth as well as a moon of the right size—and this on top of all the other considerations regarding the nature of the sun. What are the chances that all of this is coincidental?
Suppose you take your car to a trained and skilled technician for a tune-up. He diligently finishes his job, and you find everything to be in order. How do you think he will react if you later insist that the precise tune-up of your car was accomplished by mere accident or that it was the result of pure chance?
The same question may very well be asked about the exceptional nature of our sun. Some scientists would have you believe that the make-up of our sun, its orbit, its distance from the earth, and its other characteristics are all merely a fortunate coincidence. Does this make sense? Do you think it is a logical conclusion?
Just as a masterfully calibrated motor vehicle tells us something about the training and skill of the technician, so our sun—among other celestial bodies—is telling us something. The exceptional qualities of our home star that make life possible on earth convey the clear message that this star is the handiwork of an intelligent and powerful Designer and Creator. The apostle Paul put it this way: “His invisible qualities are clearly seen from the world’s creation onward, because they are perceived by the things made, even his eternal power and Godship.”—Romans 1:20.
For more information on the Oort cloud, see the Awake! of July 22, 1999, page 26.
[Blurb on page 17]
Only about half a billionth of the sun’s energy output reaches our planet
[Picture on page 16]
Solar outbursts like this one have not endangered life on earth
Pages 2, 15, and 16: NASA photo
[Picture on page 17]
A coincidence? A size match between the sun and the moon makes for spectacular eclipses
[Picture on page 18]
If the orbit of the sun were different, a catastrophic rain of comets could bombard the earth