Looking up at the big, bright full phase Moon this week and fall under the spell of moonlight’s mesmerizing experience, just like Native Americans who called this the “Flower Moon.”
But do you know what you’re looking at? Well, you know it’s not made of green cheese! Here are some lunar facts to ponder.
Earth’s diameter is 7,926 miles, while the Moon is better than one-fourth that at 2,160 miles across. The average distance apart is 238,850 miles. That varies by in an ellipse with closest (perigee) at 225,623 miles, and farthest (apogee) 252,088 miles.
There are only five other moons in the Solar System bigger than Earth’s. Jupiter’s Ganymede, Callisto and Europa, Saturn’s Titan and Neptune’s Triton.
Everybody looks up at the Moon. Though it seems huge in our mind’s eye, you can cover it up with an outstretched pinky finger. That’s just one-half degree of the sky. This proves that as large as the Moon looks to our human eyes, it is quite tiny in the sky. That half-degree width of the Moon means that 360 Moons would span end-to-end from one horizon to directly overhead to the other horizon!
When near the horizon rising or setting against the backdrop of buildings, mountain and trees, the Moon looks huge. It’s called the “moon illusion” and several books have been written about this optical illusion in our minds.
The Moon is always the same size each night varying slightly in its elliptical orbit each month. Yes, there is a “Super Moon” sometimes when the full phase syncs with the closest point (perigee) in its orbit. But you can’t tell with your eye—and you can still cover it up with an arms-length pinky finger!
Orbiting the Earth at a speed of 2,100 mph, the Moon moves to the left, or eastward, much faster than the 1,100-mph eastward spin of the Earth’s rotation. So, the Moon keeps ahead of the Earth’s spin, and in fact, moves its own diameter eastward every hour. That means that from one night to the next, the Moon has moved 12.5 degrees in 24 hours from its position in the constellations of the Zodiac.
The Moon is also moving away from Earth at the rate of nearly two inches a year. One billion years ago, the Moon was only 100,000 miles away, whizzing around the Earth in seven hours instead of today’s 27 days!
Because of the time lag caused by the rotation of the Earth, the time between Full Moon to the next Full Moon is 29.5 days—the basis for the calendar time as marked by civilizations since antiquity. With its sphere locked as one side faces Earth and the other side remains unseen, because of a wobble in the Moon called “liberation,” we see about 59 per cent of the lunar surface as it rocks back and forth throughout the year.
The six Apollo lunar landings from 1969-72 brought back almost 1,000 pounds of rock that proved the Moon was ripped out of the Earth some 4.6 billion years ago by an unknown body whizzing through the early Solar System. So, the Moon is made up of the outer layers of a primordial Earth and is extremely light. That makes its gravity pull only one-sixth that of Earth—you’d weigh less than 17% of your current size.
That familiar line on the lunar globe that separates night from day is called the “terminator.” On Earth, our terminator marks evening or morning twilight, just like on the Moon. But without a blanket of atmosphere, the difference from night to day on the moon is a huge temperature swing. The temperature in the bright areas is around 250 degrees F., while the black, shadowed areas are around -250 F. degrees below zero—a 500 F. degree swing!
Lunar brightness is deceiving as the Moon is made up of material as dark as a lump of coal. The dark Moon rocks reflect only 12 per cent of the sunlight that strike them. If the surface was a better reflector, say 50 percent, then night life of creatures on Earth might have evolved differently.
Apollo astronauts said moon dust in their spaceship smelled like gunpowder, which makes sense. All the violent impacts with cosmic rocks are evident in craters from hundreds of miles wide to micrometeorites seen with microscopes.
For all you chemist types, here is the chemical makeup of lunar soil: Oxygen 40% Silicon 20% Iron 12% Calcium 8.5% Aluminum 7% Magnesium 5% Titanium 5% traces of Sodium, Chromium, Manganese, Potassium, Sulfur and Carbon.
Twelve sets of footprints and tire tracks from three Lunar Rovers will last for millions of years. No natural forces of erosion will wipe them away; the Moon’s barely detectable, 10 tons of atmosphere has no impact. Instead the indentations in the moon dust will be worn away by the millennium of micrometeorites showers.
Tons of buried frozen water was discovered in the Moon’s north and south poles by Lunar Prospector in 1998. Radar detected hydrogen bound up in frozen water, and NASA estimates there is between one and six billion tons of ice buried beneath 18 inches of dry lunar soil. One billion tons of water would fill 300,000 Olympic-size swimming pools.
Looking at the Moon in binoculars or a small telescope will reveal the dark, dry lava seas and hundreds of craters caused by impacts from space rocks over billions of years. All of the more than 30,000 craters visible from Earth have names, and that catalog began in the mid-1600s when it was agreed that craters be named after dead scientists, artists, philosophers, explorers and scholars. Thus, the prominent craters are called Copernicus, Archimedes, Tycho and Plato, for example.
This naming of lunar craters was given a more modern tone when the Apollo astronauts called their landmarks as seen from orbit with jargon like Cone Crater, Snowman and the like. Deceased space pioneers, and the Apollo 11moon voyagers have been honored with small craters named them.
Get your share of moonlight this week, and marvel at how man has conquered this alien world that patiently awaits the next human footprints from future explorers.