Cumberland Times-News


September 10, 2011

Where did the moon come from?

It has been nearly 40 years since the last human walked on the moon. Analysis of our Moon’s rocks has given rise to a very interesting theory as to how our Moon came to be.

Moon rocks have the same basic chemical composition as Earth rocks except for the near absence of volatile elements (would be vaporized at lower temperatures).

Could the moon’s material have come from Earth? William Hartmann, an astronomer at University of Arizona was first to propose that our Moon formed from debris of a planetary collision.

In this collision, the Earth was dealt a glancing blow by another planet about the size of Mars. The intruding planet was shattered and a large amount of the Earth’s mantle was hurled into space.

Some of this material went into orbit about the Earth, forming a ring of debris. Within this ring was a concentration of material that formed our moon.

The early moon was much closer to the Earth than it is now. The mechanism to drive the moon out further was the friction of our moon’s tides against the ocean floor. This friction slowly lengthened the Earth’s rotation period.

But to conserve rotational motion of the Earth-Moon system, the moon was pushed faster around its orbit, increasing its distance. This has resulted in our Moon now about 60 Earth radii from us.

The best indications that our moon resulted from a planetary collision is to simulate this event on a supercomputer. Different sized planets were hurled at the Earth in computer simulations.

At certain impact velocities, the smaller planet would be destroyed and large amounts of Earth middle layer (the Mantle) were ejected. The Earth’s iron-nickel core would have survived. This core gave the Earth enough mass to build itself back up.

Some of the ejected mantle material would have gone into a near Earth orbit, of which about 1/2 congealed into the moon.

Can this theory of our moon’s origin be proven? No, as you can’t prove a theory; it can only be disproven if you have observations that go against a theory.

But over the past two decades, most astronomers have accepted the “Giant Impact Theory” as being the most likely way for the moon to have formed.

The other proposed theories don’t explain the chemistry of moon rocks, or are inconsistent with physical laws. (One flawed explanation is that the Earth spun so fast that a chunk flew off; the ‘wound left behind’ is the Pacific Ocean basin.)

Today our Frostburg State Planetarium reopens for our final fall season. Early in 2012, Tawes Hall will be torn down and our programs will then be presented on Sundays in Compton Science Center on a large flat screen. A new planetarium will be put into the new building (called CCIT), slated to open in 2014.

Today’s program is “Moon Curiosities,” all about the most unusual moons in our solar system. We first cover the evening sky sights for the entire fall season and acquaint our audience with the brightest evening sky sights. There are free sky charts available in our rack as you leave.

Our free showings are at 4 p.m. and 7 p.m. in Tawes 302. The Planetarium is just off Tawes’ front lobby that faces the Compton Science Center.

The easiest way to reach the Planetarium is to take Exit 33 off Interstate 68 and drive North towards Frostburg. You will then be on Braddock Road, passing by the new housing project (Braddock Green) and some private homes on the right.

Look for FSU’s main entrance on the left, turn in and then turn to your right. After driving several hundred feet, you will see the large Performing Arts Center (PAC). Park near the PAC building and walk around it on the right. You will see Tawes Hall further down the street and the Compton Science Center on your right.

“Moon Curiosities” starts with the usual regularities of moons, then considers our moon. Our moon is the nearest moon to the sun as both Mercury and Venus are moonless.

Tonight, by coincidence, the moon is full. This is the Harvest Moon, the full moon closest to the first day of fall. You will notice much early evening moonlight for the next five evenings (weather permitting).

Returning to our program, we next take up the pygmy moons of Mars that scurry about Mars from 7.3 to 30.3 of our hours. The smaller of the two moons, Deimos is about as long as the island of Manhattan, the best known part of New York City. 

Jupiter has four big moons, each with different surface features; one moon is covered with active volcanoes while the outer big moon is covered with icy craters that have flattened out over the billions of years since they were formed.  

Saturn has a huge moon with an atmosphere thicker than Earth’s and is covered with lakes of hydrocarbons. The medium sized moons closer to Saturn cause gaps in the rings; two small moons orbit on either side of Saturn’s narrow F ring. 

Uranus rolls on its side as it orbits the sun. Uranus’ major moons also orbit side wards around the planet. Uranus’ bigger moons are named after characters in Shakespeare’s play, “The Tempest.” 

Neptune in many ways is a twin to Uranus, but without Uranus’ side wards tilt. Neptune has a big moon (Triton) orbiting backwards; instead of slowly drifting outwards (as our moon does), Triton is spiraling in! In the far future, Triton will be torn apart by Neptune’s tides, giving Neptune a magnificent ring.  

The dwarf planets also have moons. (Dwarf planets orbit the sun, are roughly spherical but have a significant amount of debris across their orbits.) Pluto is the most famed dwarf planet; recently a fourth moon about Pluto was discovered. Another dwarf planet (Eris) is slightly larger than Pluto and also has a moon. 

Enjoy the Harvest Moon both tonight and tomorrow night (actual time of full moon is 5:26 a.m. tomorrow). On Thursday and Friday evenings the moon will be near the bright planet Jupiter, shining steadily low in the east.

Bob Doyle invites any readers comments and questions. E-mail him at . He is available as a speaker on his column topics.

Text Only
  • Wildfires Wildfires

    The huge woods fire in nearby Pennsylvania shows just how much devastation can take place when a blaze breaks out during early spring. In this case, 900 acres of forest — much of it public game land — became engulfed in flames.

    April 23, 2014 1 Photo

  • Restore them Restore them

    There are an estimated 47,000 deceased veterans whose remains are unidentified and unclaimed throughout the U.S. A group of senators and congressmen hope to do something to
    bring these men and women some dignity after death.

    April 20, 2014 1 Photo

  • Happy Easter

    For the world’s more than 2 billion Christians, Easter is the day that defines their faith.
    The exact date of Christ’s resurrection is unknown, and even the precise locations of his crucifixion and burial are uncertain. This hasn’t stopped some people from saying they know the answer to these questions and others from trying to find out for themselves, or simply arguing about it.

    April 20, 2014

  • Odds are good that you didn’t know this

    Odds or Probabilities fascinate many people. There is a special website called and an accompanying location on Facebook at /BookofOdds .This website lists 400,000 odds. Three of the people who are involved in this media display have coauthored a book, “The Book of Odds” that presents some of key odds, drawing from polls and statistics published in journals. The authors are A. Shapiro, L.F. Campbell and R. Wright. This paperback was published this year by Harper Collins with ISBN 978-0-06-206085-3.

    April 20, 2014

  • Trivial questions you don’t have to answer

    Every so often in this life, my mind, all on its own, generates questions that have no real answers. So I have decided to pass them on to you. I’m tired of them. If you come up with any answers, let me know. Remember when TV jealously guarded the time zone before 9 p.m. for wholesome shows that children could watch. My gosh, how many years ago was that? It seems like another world nowadays, when you can see murders, torture and rape, or those implied, every hour on the hour, somewhere on your public screen. It might be comforting then, to remember that most children nowadays are glued to their little machines with whole different worlds on them, that they can access all day long. Except that in these different worlds they also can view murders, torture and rape on demand.

    April 20, 2014

  • Think it’s not a small world? You’re wrong

    Yes, you read that right in the paper a couple of weeks ago. I covered a wedding as a newspaper reporter. I’ve retired from doing regular stories because my primary duties lie elsewhere, and I don’t have the time or mental energy for it. But I agreed to do it for a couple of reasons, one of which goes back more than 40 years. The former proprietor of The Famous North End Tavern told me about a wedding that was to take place at the Lions Center for Rehabilitation and Extended Care, where his wife works.

    April 20, 2014

  • No Bambi for you, Mrs. Doe

    Some people want so badly for deer birth control to work that they actually think it will, even on wild populations.
    I wish I had a couple bridges to sell.
    A week ago on the Outdoors page we ran the deer there do what deer  everywhere do. They eat the easiest food available such as gardens and ornamental plantings. They walk in front of moving cars. They give ticks and  parasites a place to live.

    April 19, 2014

  • We concur We concur

    We’re certain that Donald Rumsfeld, who served as Secretary of Defense under Presidents Gerald Ford and George W. Bush, echoes what many Americans feel about the complexity of filing income tax returns.
    When he filed his return, Rumsfeld sent the following letter to the Internal Revenue Service:

    April 16, 2014 1 Photo

  • Library week

    Public libraries remain one of the best uses of taxpayer dollars. They are open to all. Young or old, poor or wealthy, residents can use computers and read current magazines and newspapers. Compact discs featuring a wide variety of music and
    movies on DVD may be checked out in addition to novels and other books.

    April 13, 2014

  • Terps need to move and move quickly

    The good news is Maryland will never have to play another basketball game in the Atlantic Coast Conference. Goodbye, good riddance, sayonara, smell ya, no more of you, stay classy, we won’t let the door hit us on the way out.
    Until we see you in court.

    April 13, 2014