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June 24

Star colors

We know that:

The color sequence of stars is that M stars are red, K=orange, G=yellow, F=yellowish white, A=white, B=bluish white, and O=blue. The sun is a G star. But I keep hearing that the sun is white. Does a correction need to be made?? is G really white (as opposed to A being white that we learn from this sequence)?? Georgia guy (talk) 01:43, 24 June 2024 (UTC)[reply]

See stellar classification, particularly the section on conventional colour description. The peak spectrum of the Sun is around yellow. As far as we are concerned using our eyes the Sun is white. As far as astronomers using instruments are concerned, it is slightly yellow. Hotter stars are comparatively bluer, and cooler stars are comparatively redder. Stars are so bright that each one at the same apparent luminosity will appear as a shade of white tinged with something else, at least for humans that evolved under the Sun's particular spectrum. What we call a "red" star, i.e. Betelgeuse, is only red by comparison - it's really kind of pink as far as we're concerned, and that's kind of an extreme example. Acroterion (talk) 01:51, 24 June 2024 (UTC)[reply]

The Sun is white because, almost per definition, white is the colour of the visible spectrum of the light emitted by our sun. Snow is white because it reflects this light uniformly. --Lambiam 05:51, 24 June 2024 (UTC)[reply]

Colour perception can be weird. Some observers see Beta Librae (Zubeneschamali) as green, even though that shouldn't be possible since green is in the middle of the visible spectrum. Double sharp (talk) 07:31, 24 June 2024 (UTC)[reply]

The sun is, to our eyes, white, more or less by definition. The white balance of our eyes automatically adjusts itself to the colour of ambient light and the sun provides most of our ambient light, making sunlight white.

Astronomers usually express colours in a number, not a word. You take the magnitude of an object as measured through a particular colour filter, do it again through a different filter and find the difference. Magnitudes are logarithmic, so this is the logarithm of the ratio of brightnesses in two wavelength bands. See colour index. Traditionally, magnitudes are calibrated such that the magnitude of Vega is zero in every band. That makes the colour index of Vega, an A0 star, zero. If you say that a colour index of zero means white, than Vega is white and the Sun is yellow. But as every photographer knows, there's no absolute truth in white balance.

Not all stars have a spectrum close to a black body. Strange colours do occur. PiusImpavidus (talk) 10:27, 24 June 2024 (UTC)[reply]

Interesting. Phil Plait explains Beta Librae along those lines in one column, noting that it is a young star and a rapid rotator. Double sharp (talk) 12:26, 24 June 2024 (UTC)[reply]

I haven't seen anyone mention that the reason we think of the Sun as "yellow" is that this is its color when it's low in the sky (but not low enough to be orange), and when it's higher than that, we can't (and definitely shouldn't) look at it for more than a split second. However if there's a bit of cloud cover that you can view the Sun through (at your own risk!) higher in the sky, you'll see it as white.

Now, to be honest, I don't have a source for that being the reason. But it does seem pretty obvious. --Trovatore (talk) 00:51, 25 June 2024 (UTC)[reply]

There's probably a discussion about that somewhere, but yes, the only time humans can safely examine the sun and assess its color, even for an instant, is when it's low on the horizon and yellow, orange, or red according to atmospheric conditions, and because we associate warm colors with, well, the warmth of the sun. There's also a lot of yellow sun cultural baggage that starts in preschool - ask a child to draw the sun and they'll reach for the yellow crayon. And as PiusImpavidus notes, white balance is what we decide it is."Daylight" light bulbs that mimic the sun's color temperature appear distinctly blue to humans used to orangey domestic lights. Acroterion (talk) 12:07, 26 June 2024 (UTC)[reply]

I mean, you probably shouldn't replicate this experiment, but FWIW, the midday sun looked white to me when I accidentally glanced at it. :) Double sharp (talk) 14:49, 26 June 2024 (UTC)[reply]

Other intelligent hominids

I heard that, although we usually think that Human intelligence (or at least human-like) is exclusive of humans, other species of hominids were also capable of it. The best known one, the Neanderthal. They are extinct, so human-like intelligence is exclusive of us now, but not in the history of evolution.

But which are, then, the specific species that developed such intelligence, as opposed to being just very smart animals? Hominidae is clearly not, as gorillas and chimpanzees are not in that level. Is it Homo? Is it Archaic humans? Are either of those composed only of intelligent creatures, excluding non-intelligent ones, or are they groups of related species regardless of intelligence? Cambalachero (talk) 02:51, 24 June 2024 (UTC)[reply]

Neanderthals are an archaic human species; Homo is a genus including modern and archaic humans. Intelligence is a concept that is very hard to define. Human intelligence arose in a long process of evolution; it is impossible to point out a specific point where the intelligence of our progenitors became "human", both because this did not leave a traceable paleoanthropological record and – more importantly – because it is not possible to define the boundary between "pre-human intelligence" and "human intelligence". For the little that is known, see Evolution of human intelligence. --Lambiam 04:30, 24 June 2024 (UTC)[reply]

Ancestry / evolution of the domestic cat

I have seen conflicting claims about whether the domestic cat descends from the European Wildcat or from the African Wildcat. Cat#Evolution shows two phylogenies: one (based on analysis of nuclear DNA) which shows the domestic cat being most closely related to the European Wildcat (and the Domestic/European Wildcat group being a sister group of the African Wildcat/Chinese Mountain Cat). The other (based on mitochondrial DNA) shows the domestic cat being descended from the African Wildcat. What does this actually mean? Is it just a case of "data from different sources is contradictory and we haven't got a conclusive answer yet"? Or does it mean that domestic cats are descended from male European wildcats that mated with African females? Or something else? Iapetus (talk) 12:07, 24 June 2024 (UTC)[reply]

Well mitochondrial DNA is inherited from the mother, so it means that the mother of the mother of the mother of the mother of the mother of the mother ..... of a domestic cat is an African wildcat. Many other ancestors could be European wildcats. Can these two kinds of wild cat interbreed? Graeme Bartlett (talk) 22:48, 24 June 2024 (UTC)[reply]

Yes. 2A0D:6FC0:84F:DF00:30E3:AD05:B7F9:443A (talk) 23:45, 24 June 2024 (UTC)[reply]

Both phylogenies can be brought into agreement in the following scenario. African wild cats were domesticated. It seems plausible that cats were first domesticated in Egypt or thereabouts. These domesticated African cats were brought to Europe and interbred with wild European cats. When a male domestic cat interbred with a female wild cat, the hybrid offspring was born in the wild and, being hybrid, was not so likely to survive, keeping the European wild cat distinct from the African wild cat. When a female domestic cat interbred with a male wild cat, the hybrid offspring was born in captivity and likely to survive as a domestic cat, making the European domestic cat evolve towards the European wild cat, whilst keeping the African mitochondrial DNA.

There's also selection pressure on domestic cats, keeping them distinct from European wild cats. PiusImpavidus (talk) 11:25, 25 June 2024 (UTC)[reply]

However, in the UK (where latterly the species has only survived in Scotland) the population of Scottish wildcats has significantly hybridised with domestic cats. Active breeding and re-introduction programs are taking place to counter this. (The poster foremrly known as 87.81.230.195} 151.227.226.178 (talk) 16:08, 25 June 2024 (UTC)[reply]

Dilution

I have a bottle of 50 ml with cypermethrin. The instructions by the manufacturer say diluire al 2-3% in acqua. Do they mean I must dilute it to a 2% to 3% solution (for example mix with 2 liters of water which will give a 2.4% to 2.5% solution)? Thank you. Hevesli (talk) 17:24, 24 June 2024 (UTC)[reply]

Yes you could do it that way. But if you don't want to use 2 litres of solution you could mix less, say half of it in 1 liter or 1 ml in 50 ml of water. Graeme Bartlett (talk) 22:51, 24 June 2024 (UTC)[reply]

Is the sun upside down in the Southern Hemisphere

I have heard that the moon is upside down in Australia but I don't know if the sun is also upside down in Australia. Can anyone tell me because I am curious. 2001:8003:429D:4100:20F0:744E:F9F2:D791 (talk) 23:10, 24 June 2024 (UTC)[reply]

If you check out the angle of the person on the Earth, say from someone at 45° north going to someone 45° south, the difference is 90°, so the appearance is sideways on. But from north pole to south pole it is rotated a full 180°. But at the poles it will be hard to see the sun from both at the same time. With the Sun it is harder to see it is rotated or not, as normally you won't be able to see any detail on the sun. With sunspots your could see something with the right equipment. But not only movement around the Earth will rotate the view of the sky, looking at moonrise and moonset will see that the moon has rotated in the sky for you. The same will apply to the Sun. Graeme Bartlett (talk) 23:51, 24 June 2024 (UTC)[reply]

Twice per year on the Equinox the Sun can be seen on the horizon simultaneously from both the North and South poles. Philvoids (talk) 17:54, 25 June 2024 (UTC)[reply]

Above the horizon as the centers will be 8 to 9 angular seconds below the horizon (parallax) but mean upward refraction is 34 angular minutes at the horizon it'd have to be less than half Earth average refraction for the circa 16 angular minute tall lower half to not clear the horizon. If the horizon isn't flat perhaps from icebergs it would be harder. Sagittarian Milky Way (talk) 22:17, 25 June 2024 (UTC)[reply]

Regarding the moon being "upside down", it depends how you're standing when you're looking up at it. The natural thing to do is to look up at the narrower angle. But if you turn around (and have something to lean back on or are very well balanced), you can look up at it at a wider angle, and it will appear the way someone in the opposite hemisphere would normally look up at it. And I would think the same would apply to the sun. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:37, 25 June 2024 (UTC)[reply]

When somebody is looking south at some object in the sky from Japan, and somebody else is looking north at the same object from Australia, the object will appear upside down for the person from Australia, because that person is upside down compared to the one in Japan. It doesn't matter what you're looking at: Moon, Sun, constellations, planets, alien spaceships... PiusImpavidus (talk) 11:36, 25 June 2024 (UTC)[reply]

Neither person is "upside-down" compared to the other. Tokyo, for instance, is about 7,800 km from Sydney. That's just under 1/5 of the Earth's circumference, so the two people are oriented about 72° apart, not 180°. --142.112.148.225 (talk) 19:08, 25 June 2024 (UTC)[reply]
This is bullshit. At sunrise or sunset on an equinox it's about 72° Sydney latitude vs Tokyo latitude same longitude but at noon on a sundial all other places same longitude will be 180° so long as the Sun's declination is between the 2 places. If the 2 latitudes are above 23.44 and below minus 23.44 respectively the Sun's declination will always be in between from now till over 10,000 years from now. Sagittarian Milky Way (talk) 22:35, 25 June 2024 (UTC)[reply]

Projected onto the plane perpendicular to the line Earth–Sun, one is upside down relative to the other. It's fair to make this projection, because either observer projects the orientation of the Sun onto his own vertical. PiusImpavidus (talk) 07:49, 26 June 2024 (UTC)[reply]

The image I put up here (not to scale) should make this somewhat intuitive. Imagine that the sunspots happen to make a face, so that an observer sticking their head up at the North Pole sees it "upside up". Clearly, an observer peeking out from the South Pole will then see it upside down. --Lambiam 12:49, 25 June 2024 (UTC)[reply]

That's very helpful; thank you. I've long known of the phenomenon, but always struggled to picture it. Matt Deres (talk) 17:33, 26 June 2024 (UTC)[reply]