The world was excited last week about the Super Moon in the sky but before we move on to the next celestial excitement, let’s ponder a beautiful coincidence regarding the apparent sizes of the Moon with respect to the Sun and the orbital distances of the Moon/Earth and Earth/Sun systems.
The full moon last week was called ‘Super’ because it occurred when the moon was at its perigee point of its orbit around Earth. As Kepler’s 1st law taught us, all celestial bodies orbit in ellipses (not perfect circles) with the larger body residing at one of 2 foci of the elliptical orbit. The two end points of the orbit are called the perigee (for the point closest to the foci where the larger body resides) and the other point is apogee (for the point farthest to the foci where the larger body resides). The Moon orbits the Earth in this same manner and when the moon is at perigee and when the Earth is between a line occupied by the Moon and Sun (Full Moon) we call this the Super Moon.
The size of the moon during this past Super Moon was only about 14% larger than normal Full Moons but it was enough for us to notice it with our naked eyes. There is a nice photo album of this past week’s Super Moon here but I’d like to turn your attention to the photo from the Astronomy Photo of the Day posted on 11-MAY-12 (note that the picture was taken on the day of perigee, 06-MAY-12).
You’ll notice that indeed the moon was slightly larger than the Sun on that day and 14 days later, on the 20th, there will be an annular eclipse of the Sun that parts of the Earth will be able to view. The annular eclipse happens when the moon is at apogee so the size of the moon (as viewed from Earth) is slightly too small to cover the entire width of the sun and there is a small sliver of an outline of the sun during this type of eclipse. When the moon is at other parts of its orbit the eclipse is total which means the entire Sun is covered.
So depending on where the moon is in its orbit around Earth, the eclipse is either total or annular but for the most part, many of Earth’s inhabitants get to enjoy a solar eclipse every year (depending on where you live).
As a child, there was a total eclipse in my area of the United States and I had gone to the trouble of making a cardboard box with a hole and a viewing panel so that I could experience this rare event and I was ready to view it (knowing, even as a child, that you should NEVER look directly at an eclipse). My labors were in vain though because when the event happened, I noticed that Mother Nature had provided a much better viewing platform. There was a large Maple tree in my backyard that had a disease which produced tiny pin holes to develop in all its leaves and when I walked under that tree I was blessed to see thousands of eclipse projections on the ground! I still remember that day like it was yesterday and it was one of those special moments that can’t be planned and most likely will never be duplicated.
Now let me get to the real point of this post. Think about this – nominally, the size of the moon, the size of the sun, the orbital distance of the moon around the Earth and the orbital distance of the Earth around the Sun are just the right dimensions to provide us with an eclipse of the Sun periodically. If any of these four variables would have been different (size of the moon/Sun or orbital dimensions of the moon/Earth or Earth/Sun systems) then we would not have the pleasure of witnessing this wonderful event.
Exit Question – Is this just dumb luck or a nice perk provided to us from an Intelligent Designer?
Excellent! thanks for the great insight. Michael