So, I went off a bit on C14 dating. The trigger for this was a few people who hunted us down at an outreach event visibly shaken that the "Blood Moon" was going to be a sign of something bad happening. I asked a few questions to get an idea on where their head was at, and it turns out that John Hagee wrote a book foretelling the end of times. This "Blood Moon" is the final sign to the economy collapsing, Obama exposing himself as the true Antichrist, dogs and cats living together mass hysteria and other fluff. You get this sort of thing quite often when you do any form of science outreach, and you need to have a clear, calm, level head when you talk. I like to let the worried person talk, and ask them where they heard the misinformation, why they are worried about it etc before I go into an explanation. This lady was a bit freaked out, and she sort-of fear-babbled for several minutes before I explained what was going on.
So, first, what is a blood moon? Man, I hate this term, but just like SuperMoon, you gotta roll with it. On September 27-28 (Sunday US time) the moon will pass into the dark center of the earth's shadow from the sun. It will take about an hour to go from one side of the shadow to the other, at which point the moon will get brighter again. During total eclipse, something neat happens: the moon turns copper or red depending on the weather here on earth. The reddish hue is due the bending of light from the atmosphere; you are looking at every sunset and sunrise on earth reflecting back to us from the moon! Sunsets are red due to more blue light scattering off of the air away from our eyes, and this is why the moon turns red. The more dust and soot and other pollution in the air, the redder the eclipse will look. With all the fires in Russia and the western United States, I expect the moon to be quite red this time.
So, this "Blood Moon" is not that big of a deal. There are at least four eclipses a year and as many as seven depending on the geometry of the moon's orbit in relation to the earth and sun that year. Eclipses can only happen in January/February and August/September. The moon's movement through the sky is almost the same as the sun's; the moon is 5 degrees off. The imaginary point where the orbits cross, called a node, is in line with the earth and sun at those times. When the new moon and/or full moon are at the "node" point, you get an eclipse. ( have props with me when I do this in real life, trust me it is way easier to show than tell.)
So now you ask, what is a tetrad? A tetrad is a series of four lunar eclipses separated by six lunar months. In this tetrad each lunar eclipse is a total eclipse; the moon will be completely covered by the dark part of the earth's shadow. These series are not rare, they happen every 12-14 years or so on average and there will be 8 of these series in the 2000-2100 time period. And the eclipses in this tetrad were not even visible in the Middle East! One of the things that ticked off the Greeks was that the eclipses they predicted did not always show up as expected; some of them were on the other side of the world.
Have there been 8 tetrads since Christ? No, more like 160 or so. But this syncs up with the Jewish calendar! Correct! Judaism uses a lunar calendar with 13 lunar "months" in a year. Jewish holidays are based on the moon and this is why Jewish holidays are in different seasons year by year. Islam uses a lunar calendar as well; this is why Ramadan is in a different season every 5 or so years. Fun fact to add to this for those of us on the Roman calendar is that there are 12 and roughly 1/2 a lunar months in one of our years. This syncs up so that we get a month every 2-3 years with two full moons, aka the "Blue Moon."
Ancient used the sun, the stars and the moon to keep track of time. Stonehenge is a lunar calendar/calculator. Some of the North American Indian mounds are set to track the lunar cycles and seasons. The Mayans used the planet Venus as the basis of their calendars. We use the sun's motion through the sky to define a year.
Why is science education so important? Why bother? Why step away from the computer and "shine a light in the darkness?" Because our fellow citizens are being preyed upon, they fall into conspiracy theories and other nonsense and they are being scared shitless at the worst. When those of us who love this stuff can take the time to explain it in a way that helps others see things outside of their data bubble we do a good thing. The lady tonight was honestly scared about this stuff. Did it help her sleep better knowing it happens all the time and has been noted for thousands of years? I hope so.
My goal with my outreach programs is to help people understand what we as the human race know about the world around us so that they can laugh along with me when stuff like this comes up. Maybe if there are enough of us out there that give a damn we can make a dent in the fear and ignorance.