Starship Asterisk*

The brown tint of the pervasive dust comes partly from photoluminescence -- dust converting ultraviolet radiation to red light.

neufer wrote:

Ann wrote:

The brown tint of the pervasive dust comes partly from photoluminescence -- dust converting ultraviolet radiation to red light.

You mean the dust glows murkily reddish because of something similar to the process of ultraviolet light from hot stars ionizing nearby hydrogen, making it glow red? So that the reddish-brown dust clouds are their own sort of little "emission nebulas"?

http://www.starrywonders.com/irisst8300.html wrote:
Iris Nebula (LBN 487 / VDB 139) with associated open cluster NGC 7023
by Steve Cannistra

<<Although not officially designated as an emission nebula, closer examination ... will reveal a linear ridge on either side of SAO 19158 that represents HII emission. The peripheral regions are comprised of reddish dust that obscures light from background stars.

In the center of the nebula, there are several ruddy-colored wisps and filaments of dust that emit broad band red light, instead of reflecting the more typical blue light of a reflection nebula. These red regions represent extended red emission (ERE), which is a type of phospholuminescence associated with dust particles that are bombared by high energy UV radiation from SAO 19158.>>

More at: http://www.starrywonders.com/irisst8300.html

zbvhs wrote:
Is SAO19158 behind the dust? It doesn't seem to be carving out a cavity.

MarkBour wrote: Since the appearance of a blue nebula was stated to be similar to the reason our sky looks blue, I wonder if there is any analogous behavior in our atmosphere to what you're saying here. Would a progressively "dustier" atmosphere go through the same color progression that you're saying exists with increasing amounts of dust in a nebula?

The light at sunset, I guess. It shifts more towards red. If our atmosphere were twice as thick, would the sky appear red during the day?

http://en.wikipedia.org/wiki/1883_erupt ... al_climate wrote:
In the year following the eruption, average Northern Hemisphere summer temperatures fell by as much as 1.2 °C (2.2 °F).[9] Weather patterns continued to be chaotic for years, and temperatures did not return to normal until 1888.[9] The record rainfall that hit Southern California during the “water year” from July 1883 to June 1884 – Los Angeles received 38.18 inches (969.8 mm) and San Diego 25.97 inches (659.6 mm)[10] – has been attributed to the Krakatoa eruption.[11] There was no El Niño during that period as is normal when heavy rain occurs in Southern California,[12] but many scientists doubt this proposed causal relationship.[13]

The eruption injected an unusually large amount of sulfur dioxide (SO2) gas high into the stratosphere, which was subsequently transported by high level winds all over the planet. This led to a global increase in sulfuric acid (H2SO4) concentration in high level cirrus clouds. The resulting increase in cloud reflectivity (or albedo) would reflect more incoming light from the sun than usual, and cool the entire planet until the suspended sulfur fell to the ground as acid precipitation.[14]

http://en.wikipedia.org/wiki/1883_erupt ... al_effects wrote:
The eruption darkened the sky worldwide for years afterward, and produced spectacular sunsets throughout the world for many months. British artist William Ashcroft made thousands of colour sketches of the red sunsets half way around the world from Krakatoa in the years after the eruption. The ash caused "such vivid red sunsets that fire engines were called out in New York, Poughkeepsie, and New Haven to quench the apparent conflagration."[15]

This eruption also produced a Bishop's Ring around the sun by day, and a volcanic purple light at twilight.
In 2004, an astronomer proposed the idea that the blood red sky shown in Edvard Munch's famous 1893 painting The Scream is also an accurate depiction of the sky over Norway after the eruption.[16]

Weather watchers of the time tracked and mapped the effects on the sky. They labeled the phenomenon the "equatorial smoke stream".[17] This was the first identification of what is known today as the jet stream.[18]

For several years following the eruption it was reported that the moon appeared to be blue and sometimes green. Blue moons resulted because some of the ash clouds were filled with particles about 1 µm 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. People also saw lavender suns and, for the first time, noctilucent clouds.[15]