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The moon

January 21, 2014
By GORDON DUVAL , Adirondack Public Observatory

Our ancestors gazed at the moon with wonder. It's been a timekeeper, a prophet, a protector and a source of fuel for the imagination. Today we know the moon to be a desolate location, very inhospitable but also very important to our everyday existence. It is our closest celestial neighbor and is, in part, the reason we are here on planet Earth.

Our moon is mainly responsible for something sailors all over the world respect and depend on. The gravitational forces between the moon and Earth pull on the fluid oceans. Combine that pull with Earth's 24 hour rotation and we have tides. The moon literally pulls the water towards it, taking it away from other locations on Earth. As a result, the coastline in one part of the world experiences a high tide while a coastline in another part of the world is at low tide. The Earth's rotation then gives us two high tides and two low tides in a given location every 24 hours and 53 minutes. The extra 53 minutes is due to the fact that for the moon to move 360 degrees around Earth in 27.3 days it must move about 13 degrees/day (to the east). Earth, meanwhile, rotates 360 degrees/day or 15 degrees/hour. Hence the time from the moon being overhead one day to it being overhead the next is 24 hours plus the 53 minutes for Earth to rotate that extra 13 degrees.

Depending on the position of the moon in relation to Earth and the sun, the tides can vary in height during the course of a month. Higher than normal high tides which are accompanied by lower than normal low tides are called Spring Tides. This occurs during a full or new moon phase where the moon, Earth and sun are lined up, as shown on the diagram. Although the sun is much farther away than the moon, the sun does contribute some to the gravitational pull on the oceans and because of that, it cannot only add to the effect of the moon on tides but also compete with it. During first and third quarter phases of the moon, the sun and moon are pulling on the oceans in different directions and the result is a neap tide where the coastal ocean levels do not vary as much, giving lower than normal high tides and higher than normal low tides.

Article Photos

The ocean tides are important for those that live near the coastlines but our moon provides us with something that is very important to every living thing on Earth. The gravitational effect the moon has on our oceans also affects the entire Earth. Our planet rotates on a north-south axis that is tilted with respect to its orbit around the Sun at a relatively consistent 23-and-one-half degrees. This tilt is what provides us with predictable seasonal changes year after year. The moon's gravity helps stabilize the Earth in its orbit around the Sun and gives us a reasonable expectation that the seasons will come and go in an orderly fashion for generations to come.

Besides illuminating our night sky, causing tides and keeping Earth in its place, the moon also provides us with an event that people in the far distant future may not get to see. The moon is 400 times smaller in diameter than the sun but at this time in Earth's history, the moon is 400 times closer than the Sun. This remarkable coincidence results in the moon having the ability to completely block the sun allowing us to see the solar atmosphere known as the corona. Called a solar eclipse, it is an event well worth observing and Adirondack residents will have that opportunity on April 8, 2024 as the sun will be totally hidden by the moon at about 3:30 in the afternoon (eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2024Apr08Tgoogle.html for an interactive map). As mentioned earlier, this will not always be the case. The moon is slowly receding from the Earth due to Earth's tidal pull on it, and will eventually be too far away and appear too small to completely cover the face of the Sun. We know this due to the fact that the astronauts who walked on the moon left a mirror facing Earth so we could use lasers to accurately measure its distance.

On July 20, 1969, humans took their first steps on an ancient lava field known as the Sea of Tranquility and for a short time, represented human beings existing on another world. Since that time, much has been learned about our neighbor. We know that there are valuable mineral resources there along with the probability of water, frozen in shadowed craters near the lunar poles. In spite of its "magnificent desolation", the moon could provide us with the opportunity to establish a foothold in space from which humans could explore further into the wilderness above.

With our roll-off roof facility up and running, astronomers of the Adirondack Public Observatory are eager to dazzle you with telescopic views of the moon and cosmos every other Friday night (next on Jan. 31).

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Go to the APO web site at apobservatory.org and click on "events" for more information and directions to our site above Little Wolf Pond in Tupper Lake. Listen for Aileen on North Country Public Radio about once a month during "The Eight O'Clock Hour" or email Aileen with any questions at aodonoghue@stlawu.edu.

 
 

 

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