A minuscule chance to experience a momentous occasion

I have spent most of my scientific life dealing with minuscule issues. Nothing about astronomy and space is minuscule. For example, an “astronomical unit” is the average distance from the Earth to the sun, or about 93 million miles. These units are used to measure relatively short distances between planets or stars in a binary system. 

By contrast, 93 million micrometers are equal to about a hundred yards. I can understand that. My wife I met in the end zone of a football field. It’s a long story. But a micrometer is one millionth of a meter. Both 1,000,000 and 0.0000001 are in millions in units, but I seem to understand the latter number more easily than the first. A millionth makes sense to me, but a million somehow does not. 

The annual Perseid meteor shower occurs every year in August. The Perseids routinely provide the most popular meteor shower every year. Typically, one can see about 80 meteors in an hour during the Perseids. This year the meteor shower will peak tonight. If you watch before 11 p.m., when the moon rises, you might get a more uninterrupted view. Sunday will also offer good shows of falling stars. 

Unfortunately, this year, in 2017, the Perseids will be more difficult to see because the moon will be three-quarters full the next three nights. Rates of falling stars are likely to run 40-50 meteors per hour because the light from the moon will wash out the fainter ones. 

The grand astronomical event this year will be the solar eclipse. Solar eclipses seem to have been rare and mystical events. Historically people have been held in awe by such events. People have forever at least recorded their happenings, and sometimes they have moved people to do and record unusual things.  They have long been associated as a bad omen for kings and rulers. Don’t get your hopes up though. They have never been associated with anything to do with Congress. 

But here is the mystical part of a solar eclipse. On a specific day, the sun is shining brightly when, in the space of a very few minutes, the moon moves across its face and obliterates the light. Oh, sure, you say. Everyone knows that. But wait. The sun has a radius of about 700,000 kilometers. That is 400 times larger than the moon. How can the moon cover the sun?

Well, it turns out that the moon is 400 times closer than the sun. Since it is closer, the moon seems larger than it is in relation to the sun and, therefore, seems to cover the sun. Four hundred times larger and four hundred times farther away? Isn’t that convenient? Coincidence? I don’t think so. 

Especially when you consider that the moon’s orbit is steadily increasing by about 3.5 cm per year. Now that’s a number I can understand. That’s why the moon only sort of fits over the sun to cause an eclipse. Because of this annual change that means that eclipses haven’t always occurred and someday won’t occur anymore. 

Solar eclipses have only happened during 0.00006 percent of the Earth’s existence. And human existence on Earth just happens to occur during that small period of time. Do we know how lucky we are? Well, unless you’re a king, probably not, if big numbers and ratios sort of leave you baffled like they do me. 

Do you ever sit under the stars and wonder at the size and age of the universe? The universe is 15 billion years old and 15 billion light-years in size. There are those similar numbers again. It turns out that if the universe was substantially older, larger, younger or smaller, then conditions for our existence would not exist, let alone solar eclipses. 

Does that mean that we just happen to be here when things are as they are, or are things as they are so that we can be here? 

Gary McCallister, .(JavaScript must be enabled to view this email address), is a professor emeritus of biological sciences at Colorado Mesa University.


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