by Ann » Sun Jun 23, 2024 5:59 am
Unsurprisingly, I remember this picture from 2005 very well!
So why is the northern hemisphere of Saturn partly blue, at least when seen from certain angles? For the same reason that the cloudless daytime skies of Earth are blue, because of the way sunlight is scattered in the Earth's atmosphere and in Saturn's northern hemisphere atmosphere. So why is the southern hemisphere of Saturn apparently never blue? It's unknown, but it could be that the clouds are higher there. And as we all know, a cloudy sky is not blue.
But not only Saturn is partly blue. Jupiter is, too.
Poster of Jupiter in exaggerated color with two blue hot spots.
The hot spots of Jupiter are breaks in the cloud cover. They are not brightly blue, but they are bluer than the clouds surrounding them. Read about them
here.
Saturn's large orange moon Titan has a layer of blue haze on top of its orange haze (or cloud cover):
Pluto has a thin hazy atmosphere which is blue:
But the bluest feature in the Solar system is Saturn's E ring, which is created when sunlight is scattered in the fine particles from the icy geysers of Saturn's moon Enceladus:
The icy jets from Enceladus then form the E ring of Saturn:
All these features (with the possible exception of Jupiter's hot spots) are blue because they contain small particles which scatter blue light more efficiently than red and yellow light. So in other words, all these features are blue because they scatter blue light from the Sun more efficiently than they scatter redder light from the Sun.
And that's also why the Pleiades nebulas are so very blue. Of course, these nebulas are even bluer than the E ring, because the Seven Sisters of the Pleiades are intrinsically so much bluer than the Sun, thus providing so much more blue light to scatter.
Ann
Unsurprisingly, I remember this picture from 2005 very well! :D
[float=right][img3="Shadows of Saturn's rings on the northern blue hemisphere. Credit: NASA, ESA, Cassini imaging team. "]https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2014/06/saturn_s_shadows/14598392-1-eng-GB/Saturn_s_shadows_card_medium.jpg[/img3][/float][img3="The Colors of Saturn from Cassini.
Image Credit: NASA, ESA, JPL, ISS, Cassini Imaging Team; Processing & License: Judy Schmidt"]https://apod.nasa.gov/apod/image/2406/SaturnColors_CassiniSchmidt_960.jpg[/img3]
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So why is the northern hemisphere of Saturn partly blue, at least when seen from certain angles? For the same reason that the cloudless daytime skies of Earth are blue, because of the way sunlight is scattered in the Earth's atmosphere and in Saturn's northern hemisphere atmosphere. So why is the southern hemisphere of Saturn apparently never blue? It's unknown, but it could be that the clouds are higher there. And as we all know, a cloudy sky is not blue.
But not only Saturn is partly blue. Jupiter is, too.
[float=left][attachment=0]Jupiter poster blue hot spots.png[/attachment][c][size=85][color=#0040FF]Poster of Jupiter in exaggerated color with two blue hot spots.[/color][/size][/c][/float][float=right][img3="Line of hot spots on Jupiter. They are bluer than other features at comparable latitudes of Jupiter. Credit: Cassini/NASA."]https://nasaviz.gsfc.nasa.gov/vis/a010000/a011200/a011237/Hotspot_image1_1024.jpg[/img3][/float]
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The hot spots of Jupiter are breaks in the cloud cover. They are not brightly blue, but they are bluer than the clouds surrounding them. Read about them [url=https://nasaviz.gsfc.nasa.gov/old/11237]here[/url].
Saturn's large orange moon Titan has a layer of blue haze on top of its orange haze (or cloud cover):
[img3="Blue haze on Titan on top of its orange cloud cover. Credit: NASA/JPL/Caltech"]https://www.centauri-dreams.org/wp-content/uploads/2010/10/titan_atmos-haze.jpg[/img3]
Pluto has a thin hazy atmosphere which is blue:
[img3="Blue haze bands in Pluto's atmosphere. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute"]https://upload.wikimedia.org/wikipedia/commons/2/2a/PIA20362-Pluto-Atmosphere-Released20160114.jpg[/img3]
But the bluest feature in the Solar system is Saturn's E ring, which is created when sunlight is scattered in the fine particles from the icy geysers of Saturn's moon Enceladus:
[img3="This illustration shows the Cassini spacecraft passing through a giant vapor jet over the moon Enceladus. Credit: NASA/JPL-Caltech"]https://cdn.mos.cms.futurecdn.net/utseB6t3YKvcANaNntNGW3.jpg[/img3]
The icy jets from Enceladus then form the E ring of Saturn:
[float=left][img3="Cassini images of Enceladus in the E ring (top left, upper center) and computer-generated models of the same scenes. Views from 2006 and 2013, respectively. (NASA/JPL-Caltech/Space Science Institute)"]https://lightsinthedark.com/wp-content/uploads/2015/04/pia17191.jpg?w=600[/img3][/float][float=right][img3="The fine ice particles from the jets of Enceladus form the E ring of Saturn, which is the bluest feature in the solar system. Credit: Cassini/ESA/NASA."]https://cdn.theatlantic.com/thumbor/l11psOqiZbhe2wDso1Pw380ROus=/380x0:2621x1167/1200x625/media/img/mt/2013/11/bluedot_3300/original.jpg[/img3][/float]
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All these features (with the possible exception of Jupiter's hot spots) are blue because they contain small particles which scatter blue light more efficiently than red and yellow light. So in other words, all these features are blue because they scatter blue light from the Sun more efficiently than they scatter redder light from the Sun.
And that's also why the Pleiades nebulas are so very blue. Of course, these nebulas are even bluer than the E ring, because the Seven Sisters of the Pleiades are intrinsically so much bluer than the Sun, thus providing so much more blue light to scatter.
[img3="Blue, blue, blue, blue Pleiades! Credit: Blake Estes (iTelescope Siding Spring Obs.) & Christian Sasse"]https://apod.nasa.gov/apod/image/2212/Pleiades_Estes_1080.jpg[/img3]
Ann