SIZE    

The Moon is about 1/4 the diameter of the Earth. 

50 moons would fit inside a hollow earth. 

The average distance from the Earth to the Moon is 384,000 km. 

The precise distance between the moon and the earth was measured by placing a mirror on the surface of the moon to reflect laser light from the earth, and then by calculating the time it took the laser ray to make the round trip between the earth and the moon.

 The moon is around 384,000 km away.  The speed of light is 299,792,458 m/s.  The journey is a round trip, so:

Gravity

The gravity on the moon is 1/6 that of the Earth. To find out how much something on the Moon would weight simply take the earth weight and multiply it by (1/6), or divide by 6.  A 60-pound rock on earth would weight 10 pounds on the moon. The mass would be the same but the Moon’s gravity would be “pulling” much less than the gravity that Earth would be “pulling” on the rock.

Surface Conditions

The Moon has no atmosphere. This lack of atmosphere effects two important aspects of the moon surface conditions. 

Without an atmosphere, there is no weather on the moon, no wind, clouds, or rain. With no weather, there is no weathering process, the process of breaking down rocks either physically or chemically.  And there is no erosion process, the process of moving sediments. 

No Atmosphere = No Weathering 

There is no erosion to make footprints on the moon wash or blow away like they would here on Earth. With no weathering or erosion on the moon, there is nothing to make craters on the moon wash away like they would here on Earth.

No atmosphere on the moon results in no weathering and craters do not erode away.

Most of Earth’s craters have eroded away and are difficult to see.

Moon Formation Theories

Capture theory

While the solar system was forming, an object got to close and was captured by Earth’s gravity. 

• PROBLEM: 
  • Something would have had to slow down an object as large as the moon.
  • Similar composition

Simultaneous Formation Theory

Moon & Earth formed at the same time, the moon was just a second “eddy” of condensing rock and dust.

• PROBLEM
  • Different amounts of iron on the Earth and Moon
  • The core layers of the Earth are not the same as the Moon

Impact Theory

The moon is believed to have formed as a result of a gigantic collision between Earth and large Mars-sized object about 4.5 billion years ago, at the time the Earth had just develop its layers, with iron and nickel in the core, and silicon and oxygen in the mantle and crust.  This object hit at an angle to “splash” out some of the mantle and crust material which then condensed into the moon.  The Moon’s composition of mostly silicon and oxygen supports this theory.  The impact is also part of the reason the Earth is tilted 23 ½° off of vertical. 

Moon Geology

The oldest moon rocks we have found are 4.5 billion years old (4.5 x 10⁹). They are mostly basaltic in composition.

• Highlands – lighter colored “mountainous” areas covered in craters with older rocks 
• Maria – darker colored lowland plains. Maria is Latin for “Sea”.  Mostly smooth darker basalt rock, younger than the highland rocks 
• Rills or Rilles – valley-like linear features, probably old lava channels
• Ridges – long, narrow elevations of rock that rise out of the surface
  
• Impact Craters – formed from collision of asteroids, meteoroids, or comets
• Ejecta – rock material blasted up and outward from an impact which fell back to the surface
• Rays – long trails of ejecta which radiate outward from a crater impact

Lunar Maria (Seas)