How is it possible that our moon can completely block out our massive sun?  A total solar eclipse is a thing of wondrous precision.  At its climax, the moon perfectly covers the sun.  Perfectly.  Given the vast difference in the sizes of the two celestial bodies how is that even possible?  Our moon is only 1/400th the size of the sun.

The Eclipse…Elegance in Action

The moon is 400 times smaller than the sun which would seemingly render a total solar eclipse impossible. However, that huge difference in size is offset by the fact that the moon just happens to be almost exactly 400 times closer to earth!  That means that during a total solar eclipse, our moon, at a distance from earth of ~ 240,000 miles can perfectly cover the sun which is ~ 93,000,000 miles from earth.   Such a precise eclipse of our star is only possible due to the perfect alignment of those sizes and distances.  That marvelous alignment is also the reason the sun and the moon appear to be of equal size, from here on earth, despite their enormous differences in actual size. Just one of many such remarkably intricate workings between our earth and our nearest neighbor.

A total solar eclipse has always had profound and mesmerizing effect on us humans.  For more on that refer to a previous post.

Other Cool Facts

  • The moon is gradually pulling away from earth:  Every year the distance between the earth and the moon increases by 1.5″.  How do we know this?  During one of the Apollo moon landings astronauts left mirrors on the surface of the moon.  The distance from the earth to the moon is measured by bouncing a laser off of those mirrors.  1.5″ a year is a very incremental rate of separation but over great expanses of time it adds up.  In a million years the distance between the two bodies will be ~ 24 miles greater than it is today.  At some point in the very remote future the distance will increase to the point that a total solar eclipse will no longer be possible.


  • The speed of the earth’s rotation is slowing down:  Our rotational speed is decreasing due to secondary effects of the moon slipping away from us.  In 200 years the length of day here on earth will have increased by 4ms.  It’s doubtful that humankind will ever note such a small change but it is a reminder that nothing in space is static.

Benefits of our Moon

  • Our moon impacts the length of our day here on earth.  Without the gravitational effects of our moon our days here on earth would pass much more quickly.  Instead of a 24-hour day, the earth would complete a rotation every 8 hours.  So, instead of a 365 day year imagine a year consisting of 1095 sunrises and sunsets!


  • Without our moon the earth would be a virtual tilt-a-whirl:  Thanks to our good moon the earth sits at a consistent 23.5° (+/- 1°) angle as we orbit around the sun.  Without our moon the earth would be free to vacillate wildly—as much as +/- 10°— on its axis, much like the behavior of the other planets in our solar system.  Our poles would be constantly shifting.  This would have catastrophic effects on seasonal changes, weather patterns, and on life in general on our planet.  It has been suggested that without the moon’s calming gravitational influence life here on earth would have floundered.


  • Ocean tides:  Simply put; no moon no tides.  The oceans would be static and flat.  Many of earth’s life forms owe their origin and continued existence to our ocean tides.  A static and serene ocean would mean much less of the churning that is required to collect and move nutrient-rich materials that our oceanic life are so dependent upon.  Without those tides, life on earth may have never taken hold.

The Origin of our Moon


Eclipse-Collision with Earth

Collision with Earth

Image credit: Fahad Sulehria of

  • The result of a cosmic collision:  Approximately 4.5 billion years ago a rock estimated to be roughly the size of mars plowed into our planet.  Over time the debris created by that stupendous collision coalesced into our moon.  At that point the moon would have only been 15,000 miles from earth and would have been 16x bigger in the night sky than it is today!

Not to be Taken for Granted

Our moon is an anomaly within our solar system.  In relation to its host planet our moon is significantly larger than average.  The combination of its size and relative proximity to earth have provided our planet with distinct advantages.  Whether or not life exists elsewhere in the cosmos is yet to be determined.  However, there is no doubt that life here on our blue planet is due, in large part, to our glorious moon.  The next time you look up at it, reflect on that for a bit.

A great video…..


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