Starship Asterisk*

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

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.

http://www.robgendlerastropics.com/NGC7023text.html wrote:
<<The distinct hourglass shape of the [NGC 7023] nebula was formed by the interactions of the central star with the surrounding ambient dust cloud. HD 200775 is a B3 type pre-main sequence star known as a Herbig Be star. Herbig Ae/Be stars are intermediate mass (1-10 solar masses) pre-main sequence stars similar to their lower mass "solar size" counterparts, the T-Tauri stars. They are usually associated with dust and reflection clouds but unlike their more massive OB cousins they cannot form extended HII regions. That said, HD 200775 is one of the brightest Herbig Be stars known. With a temperature of 17000 degrees Kelvin it is hot enough to form a small HII region within a small radius of the central star. Studies of the star and nebula at radio wavelengths show the star is located within a bilobed cavity of gas whose walls delineate the exact borders of the optical nebula. The cavity is about 5 by 2.5 light years in dimension and lies in a northeast-southwest orientation. Bipolar outflows from the contracting pre-main sequence star most likely excavated the bilobed cavity which formed the template for the physical structure of the nebula. The lack of any high velocity gas within the nebula at present suggests that the outflows no longer exist.>>

More at: http://www.robgendlerastropics.com/NGC7023text.html

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.

Ann wrote:

neufer wrote:

Ann wrote: .. If there are too many dust particles between us and the star, there will either be no reflection nebula at all, or else there will be a reddened, non-blue reflection nebula. ...
Ann

hlwelborn wrote:Can anyone point me in the direction of efforts to increase astronomy studies in public schools?

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]

Ann wrote:More dust in the Earth's atmosphere would certainly make the sky less blue.

geckzilla wrote:I've heard of the sky turning completely orange or red during sandstorms. I'm curious about how accurate the photos are.

Nitpicker wrote: I can't remember whether the sun was visible or not.

geckzilla wrote:Interesting. Did not expect the sun to look like that at all.

Ann wrote:that red Earth sky, full of (reddish?) dust particles

Chris Peterson wrote:

geckzilla wrote:Interesting. Did not expect the sun to look like that at all.

What did you expect? This is a typical sunset/sunrise (enhanced by dust), with a saturated Sun looking white in the limited dynamic range image.