Cumberland Times-News

Bob Doyle - Astronomy

January 11, 2014

Our moon has seas, but not a bit of water

For most amateur sky gazers, their favorite telescopic object is the moon. This is due to the wealth of detail seen even though small telescopes.

Each night, the moon reveals different features due to the changing angle of the sun lighting the moon. From one lunar cycle to the next, the lighting is never exactly the same so that the same craters and lunar surface features will appear a little bit different.

Next fall, our observatory on top of the new CCIT building at FSU will be operational.

One of our first projects will be to make a video atlas of the moon’s near side that we can play back in our Multimedia Learning Center (40 foot tilted dome with 80 seats); this will allow our seated audience to see a large lunar image projected on the dome.

We will be able spotlight striking craters, mountain peaks and lunar rilles (crevasses).

   For this column, I am reviewing “Patrick Moore on the Moon,” his 2001 book published by Cassel & Company with ISBN 0304 354694.

Moore, who died last year, was the best known astronomy spokesperson in the world, having written many popular astronomy books on the solar system and sky atlases. Moore presented the BBC TV program, “The Sky at Night” for five decades.

   Of the seven largest moons in our solar system, our moon is closest to the sun. In terms of the Earth’s diameter (a little under 8,000 miles), our moon is about 30 Earth diameters away.

The moon is 2,160 miles in diameter. At its average distance from the Earth, our moon and our sun have nearly the same angular width. (Our sun is 400 times as far away from us as the moon, but the sun is 400 times wider than our moon.)

This allows our solar eclipses (moon covers up the sun) to be the most spectacular in our solar system. Locally, there will be two lunar eclipses this year (April and October). In a lunar eclipse, the moon moves through the Earth’s huge shadow and can be seen safely from the entire night side of the Earth.

The next total solar eclipse across the central U.S, and southern states will be in August 2017. Special sun shields are required to safely observe even a partial eclipse of the sun (as we’ll have in our area on Aug. 21, 2017.)

With your eye alone, you can see our moon’s grey plains, called the Maria (Italian for seas). Early telescopic observers assumed that the moon was just like the Earth with dark bodies of water and lighter land masses.

The grey plains were given poetic names by the Italian priest Giovanni Riccioli. The three largest grey plains are Oceanus Procellarum (Ocean of Storms), Mare Tranquillitatis (Sea of Tranquillity) and Mare Serenitatis (Sea of Serenity).

It is ironic that these names are still used, for these grey plains are actually huge lava fields with not a drop of water!

The craters are the best known lunar features. Somewhat smaller than the lava fields, they tend to be the same tint as their surroundings.

The craters are best seen with a small telescope when they are near the boundary between day and night on the moon. Then the crater rims catch the sunlight while the crater floors and surroundings are still in darkness.

The craters have been divided into two categories; the walled plains and the crater rings. The walled plains are the largest craters with a flat floor and surrounding walls. If one stood in the center of a walled plain, the curvature of the moon’s surface would be so great that the walls would be beneath the horizon.

The biggest walled plains include: Hipparchus (near moon’s center), Clavius (near southern edge of moon) and Grimaldi (near western edge of moon). The crater rings are somewhat smaller but with higher walls and often a central mountain.

The best examples of crater rings are: Theophilus (has walls three miles above crater floor), Copernicus (terraced walls and a central mountain) and Tycho (has greatest lunar ray system.

Due to our moon having an orbital period that matches its rotational period, Earth observers can only see 59 percent of the moon (called the near side).

The moon’s far side (seen by the Apollo astronauts and Lunar orbiters) lacks large lava fields and is peppered with many craters. The moon’s near side has many more interesting features than the far side.

SKY SIGHTS AHEAD: Tonight and the next four evenings, our moon will be at its best for spotting its craters and mountains with binoculars (held steadily) or a mounted telescope.

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

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Bob Doyle - Astronomy
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