Moons - Super, Blue, Black, Blood *new*

Posted By: Mona - Astronomy

Moons - Super, Blue, Black, Blood *new* - 08/13/19 07:31 PM

Social media and tabloid journalism are full of special names for the Moon and their supposed associated disasters or delights. Have you wondered what a supermoon is? Or a Blue Moon, Black Moon, or Blood Moon? Are they really rare astronomical events and portents of doom?

Moons - Super, Blue, Black, Blood
Posted By: Mona - Astronomy

Re: Moons - Super, Blue, Black, Blood *new* - 08/15/19 10:13 AM

The Moon - and to a lesser extent, the Sun - causes the tides on Earth.

At the time of the full Moon and of the new Moon, the Sun and Moon are aligned, so they pull together on the Earth. At the time of a first or third quarter Moon, the gravitational pull of the Sun and Moon are at right angles to each other.

When they pull together, we get spring tides which are higher than usual. When they pull at right angles to each other, we get neap tides which are lower than usual.

This animation shows how tides vary with Moon phase. Watch the tidal bulges of both the Sun and the Moon.

On March 11, 2011 Japan suffered a devastating earthquake and tsunami. Some claimed that it was caused by a "supermoon" which would occur on the 19th. In fact, on March 11, the Moon was just coming into its first-quarter phase, i.e., when its gravitational influence on Earth is at its lowest. Unsurprisingly, no correlation has been found between perigee full moons - aka supermoons - and major earthquakes.
Posted By: Mona - Astronomy

Re: Moons - Super, Blue, Black, Blood *new* - 08/16/19 09:29 AM

Accounts of times when the Moon actually looked blue:

1883. The Indonesian volcano Krakatoa exploded. Fully 600 km away, people heard the noise as loud as a cannon shot. Plumes of ash rose to the very top of Earth's atmosphere. And the moon turned blue.

Krakatoa's ash is the reason. Some of the ash-clouds were filled with particles about 1 micron (one millionth of a meter) wide--the right size to strongly scatter red light, while allowing other colors to pass. White moonbeams shining through the clouds emerged blue, and sometimes green.

Blue moons persisted for years after the eruption.

The key to a blue moon is having in the air lots of particles slightly wider than the wavelength of red light (0.7 micron)--and no other sizes present. This is rare, but volcanoes sometimes spit out such clouds, as do forest fires:

"On September 23, 1950, several muskeg fires that had been quietly smoldering for several years in Alberta suddenly blew up into major--and very smoky--fires," writes physics professor Sue Ann Bowling of the University of Alaska. "Winds carried the smoke eastward and southward with unusual speed, and the conditions of the fire produced large quantities of oily droplets of just the right size (about 1 micron in diameter) to scatter red and yellow light. Wherever the smoke cleared enough so that the sun was visible, it was lavender or blue. Ontario and much of the east coast of the U.S. were affected by the following day, but the smoke kept going. Two days later, observers in England reported an indigo sun in smoke-dimmed skies, followed by an equally blue moon that evening."

Dr. Tony Phillips, NASA
Posted By: Angie

Re: Moons - Super, Blue, Black, Blood *new* - 08/16/19 02:12 PM

Mother Nature is incredible.
Posted By: Mona - Astronomy

Re: Moons - Super, Blue, Black, Blood *new* - 08/17/19 11:39 AM

The color of the moon at totality in a lunar eclipse varies. It isn't always the color of blood, so calling every lunar eclipse a "blood Moon" is far from accurate. Atmospheric conditions on Earth determine the color that we'll see. For example, volcanic ash in the air makes for a dark Moon. Scientists measure the appearance and brightness of a total lunar eclipse using the five-point Danjon scale - ranging from 0 to 4.

The scale was devised by French astronomer Andre-Louis Danjon.

Posted By: Mona - Astronomy

Re: Moons - Super, Blue, Black, Blood *new* - 08/20/19 07:32 PM

British tabloid The Mirror's online version a few weeks ago informed readers:
A 'BLACK' supermoon will rise tomorrow: Rare second new moon of the month will appear huge in the sky as it reaches closest point to Earth in its orbit

Hmm. Not likely to appear huge when you can't actually see it. In fact - and in contradiction of the previous statement - later it says
Similar to a New Moon, a Black Moon cannot be seen in the night sky

It isn't similar to a new moon, all it is is a new moon.

And there's more!
tomorrow's new moon is also a supermoon, meaning it will be happening in conjunction with a lunar perigee -- the closet point to Earth in its monthly orbit.
As a result, the moon will have a drastic impact on tides.

Erm. No. It doesn't have a drastic impact.
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