APOD: Red Crepuscular Rays from an Eclipse (2022 May 30)

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APOD: Red Crepuscular Rays from an Eclipse (2022 May 30)

Post by APOD Robot » Mon May 30, 2022 4:05 am

Image Red Crepuscular Rays from an Eclipse

Explanation: What's happening behind that island? Things both expected and unexpected. Expected, perhaps, the pictured rays of light -- called crepuscular rays -- originate from the Sun. Unexpected, though, the Sun was being partially eclipsed by the Moon at the time -- late last month. Expected, perhaps, the Sun's rays are quite bright as they shine through gaps in below-horizon clouds. Unexpected, though, the crepuscular rays are quite red, likely the result an abundance of aerosols in Earth's atmosphere scattering away much of the blue light. Expected, with hope, a memorable scene featuring both the Moon and the Sun, superposed. Unfortunately, from this location -- in Uruguay looking toward Argentina -- clouds obscured the eclipse -- which wasn't completely unexpected. However, after packing up to go home, the beauty of bright red crepuscular rays emerged -- quite unexpectedly. Oh -- and that island on the horizon -- it's really two islands.

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Re: APOD: Red Crepuscular Rays from an Eclipse (2022 May 30)

Post by orin stepanek » Mon May 30, 2022 11:30 am

EclipseRays_Bouvier_960.jpg
What can I say? Utterly fascinating; so very red! 8-)
c3f50601ff95bf39d0fdeff1db42aae1.jpg
Kitty thinks so too!
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Re: APOD: Red Crepuscular Rays from an Eclipse (2022 May 30)

Post by Ann » Mon May 30, 2022 1:10 pm

There's a lot of red stuff in the Universe.

There are, for example, red hypergiants like VY Canis Majoris.


There are also red carbon stars:


There are luminous red novas like V838 Monocerotis:

Wikipedia wrote:

V838 Monocerotis (Nova Monocerotis 2002) is a spectroscopic binary star system in the constellation Monoceros about 19,000 light years (6 kpc) from the Sun. The previously unremarked star was observed in early 2002 experiencing a major outburst, and was possibly one of the largest known stars for a short period following the outburst...

The eruption occurred on one of two B3 main sequence stars in a close binary orbit. The erupting star became a very cool supergiant and for a while engulfed its companion.

There are also red rectangles in space:


There are, of course, lots and lots of red nebulas in space - I'm not too sure which one this is:



There are also brown dwarfs in space. Brown? Forget it! They are red(dish):

True color of a brown dwarf: ███

There are also, of course, Great Red Spots:


There are red planets:


There are total lunar eclipses, which are red:

Eclipsed super blood moon Jim Damaske Tampa Bay Times.png
Eclipsed super blood moon in 2018. Jim Damaske/Tampa Bay Times


There is the Earth as seen from the Moon during a full lunar eclipse, when the Earth seems to be surrounded by a ring of red fire:



So yeah, there's a lot of red stuff in the Universe. Oh, there are red crepuscular rays, too?

Fancy that.

Ann
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Re: APOD: Red Crepuscular Rays from an Eclipse (2022 May 30)

Post by Cat Gabrel » Mon May 30, 2022 1:29 pm

Thank you for making such intriguing post of wonderful photos. And of coarse thanks for the Kitty! Finding surprise cats always makes me laugh.

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Re: APOD: Red Crepuscular Rays from an Eclipse (2022 May 30)

Post by Astronymus » Mon May 30, 2022 7:53 pm

Pretty sure they opened the Lost Ark on that island.
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Re: APOD: Red Crepuscular Rays from an Eclipse (2022 May 30)

Post by johnnydeep » Mon May 30, 2022 8:52 pm

So, Ann, would you say there are more red things in the heavens than blue things? Offhand, it seems like there are. But I might have been biased by your long list of red things :)
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Re: APOD: Red Crepuscular Rays from an Eclipse (2022 May 30)

Post by Ann » Mon May 30, 2022 10:23 pm

johnnydeep wrote: Mon May 30, 2022 8:52 pm So, Ann, would you say there are more red things in the heavens than blue things? Offhand, it seems like there are. But I might have been biased by your long list of red things :)
I'd say there are, yes.

For one thing, I bet there are more cool things than hot things in the Universe, and cool things are "red" while hot things are "blue". Figuratively speaking.

But it is literally true that the visually red part of the spectrum covers a larger part of the electromagnetic spectrum than the blue part of it. Go to this page, to see wavelength to color relationship. Scroll right, toward the "red end", and you'll see that things are "all red" from 645 nm (rgb here is r: 255, g: 0 and b: 0) and it stays exactly that red (rgb = 255, 0, 0) up until 700 nm. Then the red channel intensity just slowly fades away in the infrared part of the spectrum.

Where do we find "true blue", where rgb is 0, 0, 255? We don't. The best we can do is 441 nm, where rgb is 0, 11, 255 and 439 nm, where rgb is 10, 0, 255. And while the red part of the spectrum stays "constant", and equally red for tens of nanometers, the blue part rapidly changes hue. Scroll left, and you'll see the rapid change.

Also, blue stars (which are the bluest objects in the Universe apart from a few bluish planets, whose atmosphere makes them look blue) aren't that blue. That's because all blue stars emit green, yellow and red light too, not just blue light (even though there is more blue light than green, red and yellow). So the blue light is diluted. Also, there isn't that much blue light in the spectrum of hot stars (remember that the blue part of the spectrum is narrow), because the emission of hot stars peaks in the ultraviolet. So the blue stars are really blue-white, but I'm going to call them blue in any case.


Also, blue light is strongly affected by dust reddening. Many Milky Way stars are intrinsically blue, but so much of their blue light is filtered away by intervening dust that they look white, yellow, or even reddish.

Of course, most (but not all) reflection nebulas are blue. They are "the upside" of dust reddening, where blue light is scattered our way instead of being scattered away from us. Everyone loves the Pleiades, don't they?


There are a few blue (well, bluish galaxies, big and small:


There really are "true blue planets", or at least one such planet, HD 189733b:


Read about the planet here.

And of course, there is another blue planet, which we all love dearly:


So there really are blue things in the Universe. But there are more red things than blue, I'll bet.

Of course, as Chris would say, what is "red" and what is "blue" is a matter of definition.

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Re: APOD: Red Crepuscular Rays from an Eclipse (2022 May 30)

Post by johnnydeep » Tue May 31, 2022 11:28 am

Thanks, Ann. If I'm being charitable, using your color scale page, I would consider blue from 425 - 490 nm, and red from 635 - 730 nm, giving "red" a 65 nm range and "blue" a 95 nm range. So, yes, red has about 50% more wavelength range to play in. But this is purely based on my particular eyes and esthetics.

In the long term, cosmic expansion and the heat death of the universe both conspire to favor red things. It's almost as if the entire universe has a red bias :ssmile: That is, unless things reverse course and we are subjected to a "Big Crunch".
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