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Episode 007 - The Da Vinci Glow and
The Moon

(Pawling Public Radio 103.7 FM)

Welcome to The Astronomical Almanac.
I am your host - Bob Antol. I am a local astronomer in the Pawling area (Poughquag specifically), with a passion for all things astronomical.

Astronomy is the branch of science that deals with celestial objects, space, and the physical universe as a whole. This show, The Astronomical Almanac, will make you more comfortable with these concepts so you will be able to recognize, grasp and appreciate the universe around us.

This is the The Astronomical Almanac on WPWL - Pawling Public Radio - 103.7 FM - Pawling, New York.
And today's episode is entitled The Da Vinci Glow and The Moon.

Old Business

  >   The first segment of the program is something I call Old Business. This will be devoted to answering any questions from the previous episodes or to correct anything I may have said in error.

The Astronomical Almanac will have the following format:

  1. Old Business - this segment here.
  2. Expanding Your Astronomical Vocabulary - devoted to defining astronomical terms.
  3. What's Up in the Sky This Week? - from planets to meteor showers to the space station and more!
  4. Astronomical Curiosities - exploring unique aspects of the world of astronomy.
  5. Did You Know? - a fun-filled trivia section.
  6. The Buffer Zone - personal recollections from my life as an amateur astronomer.

  <   This concludes the Old Business portion of the program. Next up ... Expanding Your Astronomical Vocabulary ...

Expanding Your Astronomical Vocabulary

The Da Vinci Glow

  >   Each week, a term (or two) will be defined laying the groundwork for a more general understanding of astronomy. This week, in Expanding Your Astronomical Vocabulary, I will be discussing ...

When you think of Leonardo Da Vinci, you probably think of the Mona Lisa or 16th-century submarines or, maybe, a certain suspenseful novel. From now on, think of the Moon.

Little-known to most, one of Leonardo's finest works is not a painting or an invention, but rather something from astronomy; he solved the ancient riddle of Earthshine. You can see Earthshine whenever there's a crescent Moon on the horizon at sunset. Look between the horns of the crescent for a ghostly image of the full Moon. That's Earthshine.

For thousands of years, humans marveled at the beauty of this "ashen glow," or "the old Moon in the new Moon's arms." But what was it? No one knew until the 16th century when Leonardo figured it out.

When the sun sets on the Moon, it gets dark, but not completely dark. There's still a source of light in the sky: the Earth. Our own planet lights up the lunar night 50 times brighter than a full Moon (as seen from Earth), producing the ashen glow. As seen from the Moon, the Earth would be about 3.75 times larger than the Moon we see from Earth.

  <   This concludes the Expanding Your Astronomical Vocabulary portion of the program. Next up ... What's Up in the Sky This Week ...

What's Up in the Sky This Week

  >   In this next segment of the program (What's Up in the Sky This Week), I will highlight events in the sky that are of interest to the average person. First up ...

  • Evening sky highlights
    20 Nov 2017 Mercury 7 degrees south of Moon
    20 Nov 2017 Saturn 3 degrees south of Moon
    23 Nov 2017 Mercury (at greatest elongation) stands 22 degrees east of the Sun
    27 Nov 2017 Neptune 1.2 degrees north of Moon

  • Morning sky highlights
    16 Nov 2017 Asteroid Vesta 0.4 degrees north of Moon
    16 Nov 2017 Jupiter 4 degrees south of Moon
    27 Nov 2017 Mars 3 degrees north of Spica

  • Upcoming meteor showers
    17 Nov Leonid meteor shower

    2017 Major Meteor Showers (Class I)

    Shower Activity Period Maximum Radiant Velocity r Max. Time Moon
    Date S. L. R.A. Dec. km/s ZHR
    Leonids (LEO) Nov 05-Dec 03 Nov 18 236.1 10:17 +21.5 69.7 2.5 15 0500 00

  <   This concludes the What's Up in the Sky This Week portion of the program. Next up ... Astronomical Curiosities ...

Astronomical Curiosities

The Moon

  >   In this segment, called Astronomical Curiosities, I will explore a unique and different aspect of the world of astronomy. Today's curiosity is ...

This is the The Astronomical Almanac on WPWL - Pawling Public Radio - 103.7 FM - Pawling, New York ... streaming live at pawlingpublicradio.org.

Moon Statistics
Mass (kg) 7.349e+22
Mass (Earth = 1) 1.2298e-02
Equatorial radius (km) 1,737.4
Equatorial radius (Earth = 1) 2.7241e-01
Mean density (gm/cm^3) 3.34
Mean distance from Earth (km) 384,400
Rotational period (days) 27.32166
Orbital period (days) 27.32166
Average length of lunar day (days) 29.53059
Mean orbital velocity (km/sec) 1.03
Orbital eccentricity 0.0549
Tilt of axis (degrees) 1.5424
Orbital inclination (degrees) 5.1454
Equatorial surface gravity (m/sec^2) 1.62
Equatorial escape velocity (km/sec) 2.38
Visual geometric albedo 0.12
Magnitude (Vo) -12.74
Mean surface temperature (day) 225°F (107°C)
Mean surface temperature (night) -307°F (-153°C)
Maximum surface temperature 253°F (123°C)
Minimum surface temperature -451°F (-233°C)

Fun Moon Facts
The "Making" of the Moon
The Moon was created when a rock the size of mars slammed into Earth, shortly after the solar system began forming about 4.5 billion years ago. The giant-impact hypothesis, sometimes called the Big Splat, or the Theia Impact suggests that

  • the Moon formed out of the debris left over from a collision between Earth and an astronomical body the size of Mars, approximately 4.5 billion years ago, in the Hadean eon; about 20 to 100 million years after the solar system coalesced.
  • The colliding body is sometimes called Theia, from the name of the mythical Greek Titan who was the mother of Selene, the goddess of the Moon.
  • Analysis of lunar rocks, published in a 2016 report, suggests that the impact may have been a direct hit, causing a thorough mixing of both parent bodies.

"Locked" in Orbit
Perhaps the coolest thing about the Moon is that it always shows us the same face (... kind of [more on libration in a future episode]). Since both the Earth and Moon are rotating and orbiting, how can this be?

Long ago, the Earth's gravitational effects slowed the Moon's rotation about its axis. Once the Moon's rotation slowed enough to match its orbital period (the time it takes the Moon to go around the Earth), the effect stabilized. Many of the moons around other planets behave similarly.

What about phases? Here's how they work: As the Moon orbits Earth, it spends part of its time between us and the Sun, and the lighted half faces away from us. This is called a New Moon. So there is no such thing as a "dark side of the Moon", just a side we never see more correctly called the "far side of the Moon".

As the Moon swings around on its orbit, a thin sliver of reflected sunlight is seen on Earth as a Crescent Moon. Once the Moon is opposite the Sun, it becomes fully lit from our view - a Full Moon.

Apollo Moon Trees
More than 400 trees on Earth came from the Moon. Well ... they came from lunar orbit. In 1971, Apollo 14 astronaut Stuart Roosa took a bunch of seeds with him and while Alan Shepard and Edgar Mitchell were busy sauntering around on the surface of the Moon, Roosa guarded his seeds.

Later, the seeds were germinated on Earth, planted at various sites around the country, and came to be called the Moon Trees. Most of them are doing just fine.

Earth's Sister Moons
The Moon is Earth's only natural satellite ... right? Maybe not. In 1999, astronomers found that a 3-mile (5 kilometer) wide asteroid may be caught in Earth's gravitational grip, thereby becoming a satellite of our planet.

Cruithne ("KROOee-nyuh"), as it is called, takes 770 years to complete a horseshoe-shaped orbit around Earth, and it will remain in a suspended state around Earth for at least 5,000 years.

Space Rock Punching Bag
The Moon's heavily cratered surface is the result of intense pummeling by space rocks between 4.1 billion and 3.8 billion years ago.

The "scars" of this war, seen as craters, have not eroded much for two main reasons:

  1. The Moon is not geologically very active, so moonquakes, volcanoes and mountain-building do not destroy the landscape as they do on Earth; and
  2. with virtually no atmosphere there is no wind or rain, so very little surface erosion occurs.

But ... there is a very, very thin layer of gases on the lunar surface that can almost be called an atmosphere. Technically, it's considered an exosphere.

In an exosphere, the gases are so spread out that they rarely collide with one another. They are rather like microscopic cannon balls flying unimpeded on curved, ballistic trajectories and bouncing across the lunar surface.

  • In the moon's atmosphere, there are only 100 molecules per cubic centimeter.
  • In comparison, Earth's atmosphere at sea level has about 100 billion billion molecules per cubic centimeter.
  • The total mass of these lunar gases is about 55,000 pounds (25,000 kilograms), about the same weight as a loaded dump truck.
  • Every night, the cold temperatures mean the atmosphere falls to the ground, only to be kicked up by the solar wind the following days.

A Lunar Egghead
The Moon is not round or spherical. Instead, it is shaped like an egg. If you go outside and look up, one of the small ends is pointing right at you. And the Moon's center of mass is not at the geometric center of the satellite; it is about 1.2 miles (2 kilometers) off-center.

Apollo astronauts used seismometers during their visits to the Moon and discovered that the gray orb is not a totally dead place, geologically speaking. Small moonquakes, originating several miles below the surface, are thought to be caused by the gravitational pull of Earth. Sometimes tiny fractures appear at the surface, and gas escapes.

Scientists say they think the Moon probably has a core that is hot and perhaps partially molten, as is Earth's core. But data from NASA's Lunar Prospector spacecraft showed in 1999 that the Moon's core is small - probably beween 2 and 4 percent of its mass. This is tiny compared with Earth, in which the iron core makes up about 30 percent of the planet's mass.

Is the Moon a Planet?
Our Moon is bigger than Pluto. And at roughly one-fourth the diameter of Earth, some scientists think the Moon is more like a planet. They refer to the Earth-Moon system as a "double planet". Pluto and its moon Charon ("KHA-ron") are also called a double-planet system by some.

Moon's Ocean Tug
Tides on Earth are caused mostly by the Moon (the Sun as a smaller effect). Here is how it works:

The Moon's gravity pulls on Earth's oceans. High tide aligns with the Moon as Earth spins underneath. Another high tide occurs on the opposite side of the planet because gravity pulls Earth toward the Moon more than it pulls the water.

  • At full Moon and new Moon, the Sun, Earth and Moon are lined up, producing the higher than normal tides (called spring tides, for the way they spring up).
  • When the Moon is at first or last quarter, smaller neap tides form.
  • The Moon's 29.5 day orbit around Earth is not quite circular. When the Moon is closest to Earth (called its perigee), spring tides are even higher, and they are called perigean spring tides.

All this tugging has another interesting effect: Some of Earth's rotational energy is stolen by the Moon, causing our planet to slow down by about 1.5 milliseconds every century.

Moon Moving Away from the Earth
The Moon is moving away from us. Each year, the Moon steals some of Earth's rotational energy, and uses it to propel itself about 1.5 inches (3.8 centimeters) higher in its orbit. When the Moon first formed, it was about 14,000 miles (22,530 kilometers) from Earth. It is now an average of 239,000 miles (385,000 kilometers) away.

  <   This concludes the Astronomical Curiosities portion of the program. Next up ... Did You Know? ...

Did You Know?

  >   This segment of the program will be devoted to little bits of trivia that can be shared at parties, family get-togethers, reunions. Hey, the next time you are at a bar and there is a lull in the conversation, simply yell out Did You Know ... and share the following!

The Moon (or Luna) is the Earth's only natural satellite and was formed 4.5 billion years ago, in the Hadean eon; about 20 to 100 million years after the solar system coalesced. The Moon is in synchronous rotation with Earth meaning the "same side" is always facing the Earth (... kind of [more on libration in a future episode]).

  <   This concludes the Did You Know? portion of the program. Next up ... The Buffer Zone ...

The Buffer Zone

  >   If there is still time left in the program, this segment (The Buffer Zone) will be devoted to 'personal recollections' of the things that initially got me interested in astronomy.

"Reading a Book" under the light of the full Moon.

The Astronomical Almanac can be found on the web at http://www.stargate4173.com/wpwl/.

  <   This concludes the The Buffer Zone portion of the program.

This has been the special James Bond edition of The Almanac, The Astronomical Almanac
on WPWL - Pawling Public Radio - 103.7 FM - Pawling, New York.
I have been your host - Antol, Bob Antol.
I hope you enjoyed today's show and are a little more comfortable with the topics I discussed so you can now more easily recognize, grasp and appreciate the universe around us.
On next week's show, the episode will be entitled Apogee, Perigee and The Supermoon.

Clear skies ... and don't forget ... to look up!

copyright © 2017 Robert A. Antol