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rtomes
2007-Sep-11, 09:56 AM
Although it is mentioned as only being a modern meaning, the concept of a Blue Moon as two full moons in the same month has caught on. I just came across an old reference to real blue moons. In Charles Fort's "Book of the Damned (http://www.gutenberg.org/etext/22472)" he states:

In the autumn of 1883, and for years afterward, occurred
brilliant-colored sunsets, such as had never been seen before within the
memory of all observers. Also there were blue moons.

I think that one is likely to smile incredulously at the notion of blue
moons. Nevertheless they were as common as were green suns in 1883.
Sounds pretty far-fetched until you read on a bit where he explains:

Science had to account for these unconventionalities. Such publications
as _Nature_ and _Knowledge_ were besieged with inquiries.

I suppose, in Alaska and in the South Sea Islands, all the medicine men
were similarly upon trial.

Something had to be thought of.

Upon the 28th of August, 1883, the volcano of Krakatoa, of the Straits
of Sunda, had blown up.

antoniseb
2007-Sep-11, 01:01 PM
Although it is mentioned as only being a modern meaning, the concept of a Blue Moon as two full moons in the same month has caught on.

Some effort has been made to correct this almost-there definition of Blue Moon. The supposed real definition is two full Moons while the Sun is in the same astrological sign (as done by the 30/31 day calendar, not actual Solar position against the sky). So if there is a full Moon on March 22nd, and the next is on April 19th, the one in April is a Blue Moon.

George
2007-Sep-12, 01:58 AM
Some effort has been made to correct this almost-there definition of Blue Moon. The supposed real definition is two full Moons while the Sun is in the same astrological sign (as done by the 30/31 day calendar, not actual Solar position against the sky). So if there is a full Moon on March 22nd, and the next is on April 19th, the one in April is a Blue Moon.

That is interesting but a little surprising since it takes a little calculating to determine where the Sun is in a constellation.

As for seeing an actual blue-looking Moon:

Certain fires and volcanoes produce a particle of just the right size to scatter light at the red end of the spectrum more than the blue end. This is known as selective scattering and it causes the Moon to appear blue since the longer wavelengths scatter away from the observer leaving the blues.

This also explains the blue halo around the Sun as seen from the Mars rovers.

eburacum45
2007-Sep-12, 04:48 AM
An eclipse I saw back in 1992 was very dark, kind of purplish blue, because of the dust of Mt Pinatubo. I haven't found anyone else who remembers that event to confirm my recollection.
In this photomontage of that eclipse it looks red, although elsewhere it is described as 'nearly invisible'.
http://www.mreclipse.com/LEphoto/TLE1992/TLE1992strip1w.JPG

hhEb09'1
2007-Sep-12, 07:37 AM
Some effort has been made to correct this almost-there definition of Blue Moon. The supposed real definition is two full Moons while the Sun is in the same astrological sign (as done by the 30/31 day calendar, not actual Solar position against the sky). So if there is a full Moon on March 22nd, and the next is on April 19th, the one in April is a Blue Moon.Supposed real definition? This is the first I've heard that one (I think!). I read both articles in Sky and Telescope where they searched for (http://www.skyandtelescope.com/observing/objects/moon/3305141.html), and then revealed (http://www.skyandtelescope.com/observing/objects/moon/3304131.html), their error in promoting the "second full moon in a month".

What is your source for that?

hhEb09'1
2007-Sep-12, 07:44 AM
In this photomontage of that eclipse it looks red, although elsewhere it is described as 'nearly invisible'.As we saw last month, closer to dawn or dusk, in the twilight, the moon will be harder to see. Where were those accounts from?

George
2007-Sep-12, 12:59 PM
An eclipse I saw back in 1992 was very dark, kind of purplish blue, because of the dust of Mt Pinatubo. I haven't found anyone else who remembers that event to confirm my recollection.
In this photomontage of that eclipse it looks red, although elsewhere it is described as 'nearly invisible'.
http://www.mreclipse.com/LEphoto/TLE1992/TLE1992strip1w.JPG
Since particle size is critical for selective scattering, perhaps location and elevation are important for viewing through the proper volcanic particle sizes necessary to scatter the reds instead of the blues.

eburacum45
2007-Sep-12, 10:18 PM
As we saw last month, closer to dawn or dusk, in the twilight, the moon will be harder to see. Where were those accounts from?
I don't know. Here is my source;
http://www.bbc.co.uk/manchester/content/articles/2007/03/02/030307_lunar_eclipse_feature.shtml

If the Earth had no atmosphere the Moon would be invisible in the Earth's shadow. However, light refracted and filtered through the atmosphere can still illuminate the Moon a little. Its appearance depends on the amount of dust in the atmosphere: following the eruption of Mount Pinatubo in 1992, the eclipsed Moon was nearly invisible. So; no names, no locations.

My recollection of this event was seeing the eclipse in the middle of the night, at an elevation of about 40 degrees or more above the horizon. The colour was apparently caused by the passage of light through the Earth's ash-laden atmosphere on its way to the Moon. An observer on the Moon looking at the Earth would probably have seen a dark (purplish blue?) ring of light, as the light of the Sun was absorbed and scattered by the volcanic particulates and very little reached the Moon.

I doubt that the colour was affected very much by the passage of the reflected light through the atmosphere to my eye, but it may have been.

George
2007-Sep-13, 12:18 AM
Though I strongly suspect selective scattering, there is yet another possibility perhaps: Chappuis absorption.

By any chance was the eclipse unusually dim? If so, perhaps the volcanic particulate increased the lower atmosphere's opacity. This would allow a greater portion of the light to pass through the tenious ozone layer which is known to produce a bluish purple band.

It is ozone that is the reason the sky is blue!! :eek:
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Ok, that statement should start trouble. :) Actually it is quite true, but not during the day as Rayleigh scattering, as you know, gets credit for our blue daytime sky. At sunset and twilight, Rayleigh scattering should give us a yellowish sky, yet it is the ozone that absorbs [much of] the colors around the region of 600nm; the long greens, yellows, oranges, and reds are absorbed. This leaves us with a blue sky. Supposedly, there is a hue difference that is discernable to the trained eye. [Darn, I was gonna make this a quiz question. Oh well. :)]

eburacum45
2007-Sep-13, 12:38 AM
Yes, it was very a dim eclipse- rated 0 on the Danjon Scale according to wikipedia
http://en.wikipedia.org/wiki/Danjon_scale

George
2007-Sep-13, 12:43 AM
Wow. Shooting from the hip sometimes works! [maybe] [Added: Every once in a while I get one right, about every blue Moon.]

Nice images.

Maybe some Goggle work will reveal more on this issue, but when I have more time.

George
2007-Sep-13, 03:44 PM
The idea that ozone is largely responsible for your purple moon may be testable. Ozone is unstable; it is constantly being created by sunlight. Therefore, I am wondering if the eastern limb of the Earth's ozone layer will produce more purple light than our western limb during a lunar eclipse since our eastern limb has had sunlight on it all day, whereas the western limb has had none. [I don't know how unstable Ozone is, admittedly, so I don't know how sound this idea really is.]

I noticed your wiki link favors purple on one side of the lunar image, but I did not check to see which side. Of course, the entire passage of the Moon through the shadow is the proper way to check this idea.

dgavin
2007-Sep-14, 12:27 AM
Although it is mentioned as only being a modern meaning, the concept of a Blue Moon as two full moons in the same month has caught on. I just came across an old reference to real blue moons. In Charles Fort's "Book of the Damned (http://www.gutenberg.org/etext/22472)" he states:

Sounds pretty far-fetched until you read on a bit where he explains:

During field burning season, and forest fire season here in Oregon quite often you can see a bright orange moon, and the sun light is a bit more shifted to the orange colors. Once I saw a red moon because the smoke in the atmosphere was so think.

During the St. Helens eruption, the moon was slightly blue hued, and the sun light seemed a tad bluer.

So yes, particles in the atmosphere do effect the light received, and can lead to different colorings of the Moon.

hhEb09'1
2007-Sep-14, 12:40 AM
Once I saw a red moon because the smoke in the atmosphere was so think.That's thick, right? Not thin? Sounds like a supermodel, though, one who was very thin and very thick. Or BAUTistas, who are also very think.

George
2007-Sep-14, 01:55 AM
Some of us thin ones are sometimes pretty thick, I think. :)

hhEb09'1
2007-Sep-14, 12:21 PM
So if there is a full Moon on March 22nd, and the next is on April 19th, the one in April is a Blue Moon.And another nit, if the full moon occurred sometime on Mar. 22, and then on Apr. 19, the time between them would be less than 29 days. I'm pretty sure that's impossible, unless the international dateline comes into play :)

George
2007-Sep-15, 11:24 PM
An eclipse I saw back in 1992 was very dark, kind of purplish blue, because of the dust of Mt Pinatubo. I haven't found anyone else who remembers that event to confirm my recollection.
In this photomontage of that eclipse it looks red, although elsewhere it is described as 'nearly invisible'.
http://www.mreclipse.com/LEphoto/TLE1992/TLE1992strip1w.JPG
This still intrigues me.

I found nothing to explain a purple Moon, surprisingly.

This site (http://books.google.com/books?id=DvNyjQ7jbDoC&pg=PT49&lpg=PT49&dq=danjon+scale+purple&source=web&ots=3DdEXMIIJS&sig=tcgP4WdZ2fA3zSPPXK14pKzFL1g]http://books.google.com/books?id=DvNyjQ7jbDoC&pg=PT49&lpg=PT49&dq=danjon+scale+purple&source=web&ots=3DdEXMIIJS&sig=tcgP4WdZ2fA3zSPPXK14pKzFL1g) mentions seeing a purple horizon as a result of the 1992 volcano.

From this site (http://blogs.irishastronomy.org/arcturus/Arcturus0311.pdf), page 12, it claims a purple color for a full Moon was observed.

"Other months, the familar rose colours of the Summer
Moon low on the horizon were on one occasion replaced by
a purple tint."

I think Chappuis absorption may be the answer for your purple eclipse, but I can find nothing to verify it.

Maksutov
2007-Sep-16, 05:01 AM
This still intrigues me.

I found nothing to explain a purple Moon, surprisingly.

This site (http://books.google.com/books?id=DvNyjQ7jbDoC&pg=PT49&lpg=PT49&dq=danjon+scale+purple&source=web&ots=3DdEXMIIJS&sig=tcgP4WdZ2fA3zSPPXK14pKzFL1g%5Dhttp://books.google.com/books?id=DvNyjQ7jbDoC&pg=PT49&lpg=PT49&dq=danjon+scale+purple&source=web&ots=3DdEXMIIJS&sig=tcgP4WdZ2fA3zSPPXK14pKzFL1g) mentions seeing a purple horizon as a result of the 1992 volcano.

From this site (http://blogs.irishastronomy.org/arcturus/Arcturus0311.pdf), page 12, it claims a purple color for a full Moon was observed.

"Other months, the familar rose colours of the Summer
Moon low on the horizon were on one occasion replaced by
a purple tint."

I think Chappuis absorption may be the answer for your purple eclipse, but I can find nothing to verify it.I always see a blue/purple band along the eastern horizon just after sunset as the Earth's shadow moves up into the sky.

But concerning a purple Moon, sometimes it's the smoke in the sky, sometimes it's the smoke in the observer.

I'm still waiting for a purplish-bluish eclipse to be called the "Hendrix Experience".

Meanwhile, having observed the Moon astronomically for close to 50 years now, I've seen red, orange, pink, white, and all their associated colors, but never blue. Perhaps after the Yellowstone caldera erupts I'll get see one of those blue ones.

If the sky is clear.

And I'm still here.

eburacum45
2007-Sep-16, 06:17 AM
This still intrigues me.

I found nothing to explain a purple Moon, surprisingly.

This site (http://books.google.com/books?id=DvNyjQ7jbDoC&pg=PT49&lpg=PT49&dq=danjon+scale+purple&source=web&ots=3DdEXMIIJS&sig=tcgP4WdZ2fA3zSPPXK14pKzFL1g]http://books.google.com/books?id=DvNyjQ7jbDoC&pg=PT49&lpg=PT49&dq=danjon+scale+purple&source=web&ots=3DdEXMIIJS&sig=tcgP4WdZ2fA3zSPPXK14pKzFL1g) mentions seeing a purple horizon as a result of the 1992 volcano.


There is your answer; if the Earth had purple horizons at sunset at that time, the purple sunset horizon light from the Earth would be the only major lightsource illuminating the Moon at totality.
An observer on the Moon would see a purplish ring where the Earth should be; I would have loved to seen that particular eclipse from the lunar surface, with the proviso of course that I could come home for breakfast next morning.

George
2007-Sep-16, 07:19 PM
The amount of air mass that sunlight must travel through to illuminate the Moon is greater than the amount of air mass sunlight must travel through to reach an observe of a sunset. I thought this might make a difference. Perhaps not, and your statement is supported...

This site (http://books.google.com/books?id=NN5S0_3dEvkC&pg=PA205&lpg=PA205&dq=%22purple+sunset%22+atmosphere+scattering&source=web&ots=W2zp99Pzi4&sig=zQB564q6TYF6bM2WwE-3EJ8o2Eo) offers the best explanation, I suppose, for what is happening. The emission of sulfur dioxide from volcanoes creates sulfuric acid particles that reach the ozone layer in the stratosphere. These additional particles create more scattering and allow the ozone to absorb more of the spectrum between blue and red (Chappuis Absorption); a purple sunset is the result.

This would easily explain the purple Moon, IMO, since Chappuis absorption would be more effective with the longer path for sunlight through the stratosphere, along with increased opacity of the lower regions due to the larger particle sizes of the volcanic discharge staying in the lower atmosphere.

George
2007-Sep-16, 07:48 PM
I always see a blue/purple band along the eastern horizon just after sunset as the Earth's shadow moves up into the sky. Are you on a mountain? [Somehow I picutred you in a jungle surrounded by cannibals. :razz:]

What you are likely seeing is the result of Chappuis absorption where the ozone absorbs the setting Sun's light and produces an arched band of purple light. Above this band is blue and below it is, supposedly, a dark grayish blue at the horizon opposite the Sun.

I saw this, too, when at Kitt Peak during the visitor night tour thing. I don't recall how they described it, as I was more impressed with seeing the Earth's shadow, which follows this purplish event. [Color never impressed me much till you characters forced its perculation within me. :)]


But concerning a purple Moon, sometimes it's the smoke in the sky, sometimes it's the smoke in the observer. I vaguely recall you once mentioned a certain drink is causal for this observation. ;)


I'm still waiting for a purplish-bluish eclipse to be called the "Hendrix Experience". I suspect it is but only within certain smoking circles. ;)


Meanwhile, having observed the Moon astronomically for close to 50 years now, I've seen red, orange, pink, white, and all their associated colors, but never blue. Perhaps after the Yellowstone caldera erupts I'll get see one of those blue ones. If you're in the area at the time, it just may be that it is you that will be blue and on the Moon. :)

George
2007-Sep-16, 08:02 PM
An observer on the Moon would see a purplish ring where the Earth should be; I would have loved to seen that particular eclipse from the lunar surface, with the proviso of course that I could come home for breakfast next morning.
Would you settle for a purplish horizon (http://antwrp.gsfc.nasa.gov/apod/ap070916.html) (today's APOD, no less :) ) as seen from outer space?

hhEb09'1
2007-Sep-21, 12:58 AM
Would you settle for a purplish horizon (http://antwrp.gsfc.nasa.gov/apod/ap070916.html) (today's APOD, no less :) ) as seen from outer space?From the link: "The MMU was replaced with the SAFER backpack propulsion unit. " Yikes, there's an acronym that makes you think.

George
2007-Sep-21, 03:03 AM
:) Hmmmm, are we missing anyone? :shifty: When the extended range units come out, will they be FARSAFER?