A Cosmic Coincidence

The recent lunar eclipse (when the moon is partially or totally in the shadow of the earth) reminded me of what can only be a coincidence concerning the sizes of the sun, earth, and moon and the distances the sun and moon are from the earth.  This coincidence involves a solar eclipse, which occurs when the moon partially or totally blocks out the sun.  A total solar eclipse is where the cosmic coincidence takes place.  For a total solar eclipse to occur, the moon has to be of a certain size and the moon has to be of a certain distance from the earth. Also, the sun is four hundred times broader than the moon, but the sun is also four hundred times farther away from the earth than the moon is from the earth.  All these things make the sun and the moon look like they are the same size, making a total solar eclipse possible.  During a total solar eclipse of the sun, you can only see the corona, the plasma atmosphere of the sun, and no other part of the sun.


One might think that the sun, earth, and moon have always been this way, and total solar eclipses have always occurred the way we see them now.  That is not true.  The moon may have been initially as close as 16,000 miles distant from the earth.  Currently it averages 238,000 miles distant from earth.  It is moving away from the earth at a rate of 1.5 inches a year.  Millions of years from now, the moon will be too far away from the earth to never again make a total solar eclipse.  Thus we are living at a time when total solar eclipses do occur, and we now have the technology to more easily study the sun's corona during the best time to study it, during a total solar eclipse.

So what does this have to do with normal life?  Not much really.  I just have always been fascinated by astronomy.  Here is an event that can only can occur if certain things are of a certain size and of a certain distance.  Also, not only do we have the technology to observe and study the event and certain aspects of the event, but we as a species are around to do so.  Man, Homo sapiens, has only been around for about 2 million years.  That is not much time when you consider that the earth is about 4 billion years old and the universe is 13 billion years old.  It has only been in the last 100 years that our technology has increased by leaps and bounds and has enabled us to to go to the moon, split the atom, and have technology like the internet, laptops, mobile devices, and iPads.  Coincidences happen all the time, but when they happen on a cosmic level, it just blows me away.  We all live on a small planet in a small part of a galaxy which is just one of billions of galaxies in the universe.  A feel fortunate to live at a time when we are developing technology that can start answering questions that man has asked for thousands of years.  I just hope I am still around to hear some of these answers.

By the way, most of the facts in this posting come from the book Chasing the Sun, by Richard Cohen.  I have just started reading it, and I highly recommend it to anyone who has an interest in astronomy in general and in the sun in particular.  Without the sun, we would not exist.  This book talks about how the sun has influenced many cultures over thousands of years and how it still influences us today.