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---------------------- 2351 - What is Behind the Man in the Moon?
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- We call it a Full Moon, but, really it’s a Half Moon. We have been looking at the same face of The Man in the Moon that has been there since shortly after it first formed 4,500,000,000 years ago.
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- The planets were formed in the accretion disk that surrounded the Sun. In the early years of the Solar System formation much of the material circling the Sun was coalescing and colliding.
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- The Earth had accreted about 70% of the mass that it has today when it was pummeled by a Mars-size planet. Mars-size is about 11% the size of today’s Earth mass. The collision was a glancing blow that pulverized the Mars-size planet and splashed a big chunk of the Earth’s crust into orbit.
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- Everything was hot and molten as the gravitational forces pulled the two orbiting bodies into their spherical shapes. When the Moon first formed from this debris the Moon was only 14,000 miles away. It took only another 1,000 years for the Moon to fully coalesce into our Moon we see today.
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- The orbiting accretion disk debris continued to impact the surfaces as meteorites. The orbiting Moon slowed down and the orbit radius expanded outward. Today it is 252,229 miles away and traveling 2,237 miles per hour in its orbit around the Earth.
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- Mass of the Moon = 7.349 * 1-^22 kilograms = 1.23% of Earth mass.
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- Mass of the Earth = 597 * 10^22 kilograms
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- Mass of Mars = 64.2 * 10^22 kilograms = 11% of Earth mass.
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- The period of the Moon’s elliptical orbit is 27.55 days.
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- The Moon immediately fell into a 1 to 1 synchronizing orbit, meaning it completes 1 revolution on its axis for each 1 revolution in orbit about the Earth. This resulted in one side of the Moon always facing the Earth.
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- The Moon, like the Earth, was and still is bombarded by meteors. Although the meteor showers were much more extensive in past than they are today, the Moon still receives over 2,000 pounds of meteor impacts on its surface each day.
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- Technically, a meteor is an interplanetary object that is bigger than a speck of dust and smaller than an asteroid. It is some of the same stuff left over from the Earth and other terrestrial planet formations.
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- The Earth is bombarded by 4,000,000,000 meteors each day. Most are minuscule in size and are quickly slowed down and burned up in the Earth’s atmosphere.
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- The Moon however has no atmosphere. Its surface gets bombarded by meteors that are not slowed down until they hit the surface. If you look at the Moon through a telescope you can easily see the results.
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- Meteor craters are on top of meteor craters on the scared surface, but, outside of continuing impacts, the Moon’s surface has not much changed in the last 3,000,000,000 years.
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- There is no weather, no erosion, no atmosphere, no wind, on plate tectonics, no volcanoes, just pockmarks and craters to change its surface. After looking at the same face for so long, science would really like to know what is going-on on the backside and the inside of the Moon.
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- Since 1969 to 2011, Apollo astronauts have landed 6 times at 6 different locations on the near side of the Moon. Each visit allowed the astronauts to spend only 3 days setting up experiments and collecting samples to return. No manned trips have occurred over the past 40 years but many different robotic missions have visited our satellite and added to our knowledge about what it is made of.
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- Like the molten Earth, the molten Moon, allowed heavier minerals to sink to the center and the lighter elements to remain on the surface. In the case of the Moon the heavier elements olivine and pyroxene sank to the bottom of the molten ocean and formed the mantle.
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- The lighter minerals floated to the surface and formed the crust. The heavier elements like iron, nickel, and sulfur sank to the center core. For some reason the crust is 37 miles thick on the near side and 50 miles thick on the far side of the Moon. We are not sure why that is?
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- As the Moon cooled it preserved some water in the form of hydroxyl. Hydroxyl is a molecule with one oxygen atom and one hydrogen atom. The hydroxyl molecule was trapped in a mineral lattice.
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- When the mineral lattice decomposes the hydroxyl is released. It quickly combines with a second hydrogen atom and becomes a water molecule. Science now thinks that the Moon contains 100 times more water than previous estimates. 50 parts per billion, but, barely 1% of the amount of water in proportion to what is on the Earth.
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- The Moon’s interior is still hot, perhaps from the decay of radioactive elements. 185 miles below the surface temperatures are 1,300 C. This is hot enough to melt the mineral periodotite.
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- The Moon is still cooling and shallow moonquakes are still occurring within 125 miles below the surface. The largest moonquake recorded was 5.9 on the Richter scale.
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- We are still learning about the Moon from 5 retro-reflectors left on the surface that has allowed lasers on Earth to measure the distances to the surface to within one inch. There are also 4 seismometers that the Apollo astronauts left on the surface.
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- Using the precision of these measurements we have determined that the Moon has a slight wobble as it rotates. This indicated to scientists that the Moon still has a liquid core.
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- What science thinks today is that the Moon has a solid iron core that is about 100 miles radius. Above that is a liquid outer core that extends out to 220 miles radius. The mantle above that extends to the crust.
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- The radius of the Moon is 1,080 miles with the curst being 37 to 50 miles thick. The diameter of the Moon is 2,160 miles. Since it is traveling 2,237 miles per hour, it travels its own diameter each hour across the sky. Measure it with your thumb at arms length it moves that diameter every hour.
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- The Moon still has much more to tell us. We still want to learn more about its evolution and the evolution of our Solar System. The Moon is like a prehistoric rock for an archeologist. We would love to explore more of its secrets.
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- The friction of the tides continues to expend energy in the gravitational tug of war between the Moon and the Earth. As a consequence the Earth’s rotation is slowing down 0.001 seconds per 100 years. You probably did not even notice that?
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- And, the Moon is spiraling away in its orbit 1.5 inches each year. I know, you will hardly notice these things. But, it will make for a nice conservation the next time you look up to see the “Half Moon“.
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- May 2, 2019 1243
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-------------------------- Friday, May 3, 2019 --------------------------
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