Science desk
< June 16	<< May \| June \| Jul >>	June 18 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

June 17[edit]

Using modern medical knowledge, what is Sarah chances of getting pregnant at the age of 90 if she had sex at her most fertile day?[edit]

“Shall a child be born to a man who is a hundred years old? Shall Sarah, who is ninety years old, bear a child?” (Genesis 17:17) Using modern medical knowledge, what is Sarah chances of getting pregnant at the age of 90 if she had sex at her most fertile day? Let's assume she never reached menopause. 49.177.234.140 (talk) 09:35, 17 June 2019 (UTC)[reply]

You're asking about a Bible myth. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:11, 17 June 2019 (UTC)[reply]

At those ages, the only real chance would be in vitro fertilization using frozen sperm and eggs from their younger days, implanted in a surrogate mother, and raised by an adoptive family, since they are unlikely to be able to bring the child to adulthood. (The surrogate mother and adoptive mother might be the same person.) SinisterLefty (talk) 11:14, 17 June 2019 (UTC)[reply]

Pretty good chances. Your "never reached menopause" assumption is the tricky one. Andy Dingley (talk) 11:44, 17 June 2019 (UTC)[reply]

Did you check menopause and Sarah#Historicity? Gem fr (talk) 15:12, 17 June 2019 (UTC)[reply]

You are using the modern definition of age as being 365.25 days long. That definition of a "year" didn't exist at the time of the Biblical stories. 68.115.219.130 (talk) 18:26, 17 June 2019 (UTC)[reply]

There was some speculation (see Methuselah#Mistranslation) that some Biblical ages were actually their ages in months, but I don't see how that could apply here, as that would mean Sarah was like 7-8 years old. SinisterLefty (talk) 19:20, 17 June 2019 (UTC)[reply]

Besides, the surprise of the pregnancy comes from her being old already. And she died at 127 ″years″. Now, for 2 cents I can add that, if those years were, say, ~6 month long, her pregnancy would had occurred at ~45y (which could be considered old), and she would have died at ~63 (a respectable age). Gem fr (talk) 19:40, 17 June 2019 (UTC)[reply]

But why would anyone measure ages in 6 month increments ? The use of months is common in hunter/gatherer societies, where the phases of the Moon are important, allowing for night hunting when the Moon is up and nearly full, and of course relating to women's periods. Annual cycles are more important to farmers, as they control the time to plant and harvest. SinisterLefty (talk) 19:51, 17 June 2019 (UTC)[reply]

well, this can happen if you mistranslate "season" into "year" in a context where a year is made of 2 seasons, which happens quite a lot, including for herders (of which Abraham was). (caveat: this is just, then again, my 2 cents). Gem fr (talk) 20:04, 17 June 2019 (UTC)[reply]

When I took ancient history (focusing on Egypt, Greece, and Rome), it was important to note that a "year" was not 365 days long. There were generally 10 months in a year. Sometimes a year had more. Sometimes it had less. A month was not a "moonth" as expected. It had been transformed into a tax cycle. Every month, people had to pay taxes. Every year, you had yearly taxes. If the government wanted more money, it was a new month. If they needed more money, it is a new month again. During war, years wizzed by faster and faster. During peace, years slowed down and took much longer to pass by. Then, with all this nonsense, the Romans wanted to normalize the calendar. That wasn't until after 400AD. So, it was hundreds of years after the stories from Genesis. If you take the variable concept of a year and add exaggeration of oral tradition, it is very easy to get people who are hundreds of years old. 68.115.219.130 (talk) 13:03, 18 June 2019 (UTC)[reply]

When you look better, it appears that romans were, at that time, just barbarians. Abraham came (so they say) from Ur, which had very solid foundations in mathematics, astronomy, etc. and used an elaborate calendar, just as good as the Julian. There is no way your explanation can hold Gem fr (talk) 19:14, 18 June 2019 (UTC)[reply]

My take is: not zero chance so it can happen, but so low chance you would make a story out of it, still remembered after millennia. Gem fr (talk) 20:13, 17 June 2019 (UTC)[reply]

Are glucocorticoids and catecholamines regulated by different systems of the body?[edit]

Are glucocorticoids and catecholamines regulated by different systems of the body? According to the book I read now "glucocorticoids secretion is regulated by hypothalamic - pituitary system" and some rows later "Catecholamines secretion is under the control of the central nervous system". Does it mean that the glucocorticoids are not regulated by the CNS? (I thought pituitary gland is a part of the CNS too. Isn't it? ) 93.126.116.89 (talk) 19:54, 17 June 2019 (UTC)[reply]

Yes and no. Glucocorticoids and catecholamines are both synthesized in and released into the bloodstream from the adrenal glands. However, glucocorticoid release is primarily regulated by the HPA system, as your book stated. Catecholamine release is controlled by the sympathetic nervous system. So, glucocorticoid release is controlled indirectly by the brain through endocrine signalling, while catecholamine release is controlled directly by action potentials transmitted through the sympathetic nerves. --47.146.63.87 (talk) 06:12, 18 June 2019 (UTC)[reply]

Our sun[edit]

What colour is it? 86.8.201.99 (talk) 22:22, 17 June 2019 (UTC)[reply]

The Sun is a yellow dwarf, but it is actually white. This is obvious when you see the Sun high overhead, through a layer of clouds (note: I make no representation as to how dangerous it might be to look at the Sun this way).

I think the reason most people think the Sun is yellow is that it looks yellow in the late afternoon (or early morning, I suppose, if you're that sort of person) when it is low enough in the sky to look at briefly without having a reflex to look away immediately. --Trovatore (talk) 22:33, 17 June 2019 (UTC)[reply]

It can also look red or orange when near the horizon, depending on atmospheric conditions. Looking at pictures of solar eclipses, the corona appears white. And using a primitive but effective cardboard box with a pinhole "projector", again the image looks white. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:09, 18 June 2019 (UTC)[reply]

It can even sometimes appear green. SinisterLefty (talk) 02:09, 18 June 2019 (UTC)[reply]

If it's millions of degrees why isn't it blue even in photographs? If a googolplex Celsius blackbody is blue why is lightning violet? Sagittarian Milky Way (talk) 00:20, 18 June 2019 (UTC)≈[reply]

Our article says the Sun's surface temperature is 5778 K, or 9941 °F, so not close to "millions of degrees". The core reaches millions of degrees, to be sure, but those photons don't make it to the surface. --Trovatore (talk) 00:38, 18 June 2019 (UTC)[reply]

I know that. The corona is extremely hot. If it wasn't orders of magnitudes less dense than the photosphere it'd be astoundingly bright. Is the visible light part of the emission lines distributed such that it isn't strongly colored? Sagittarian Milky Way (talk) 02:17, 18 June 2019 (UTC)[reply]

According to corona, "[t]he corona is 10^-12 times as dense as the photosphere, and so produces about one-millionth as much visible light." So for purposes of everyday viewing it doesn't matter what color it is, because you can't see it next to the Sun anyway. It can be viewed during a total eclipse, and if what you mean to ask is for an explanation of the perceived color of that, I guess I don't know, but it was hardly clear that that was what you were asking. --Trovatore (talk) 02:43, 18 June 2019 (UTC)[reply]

The article on Lightning says its color is kind of blue-white, not violet. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:01, 18 June 2019 (UTC)[reply]

The sky around the lightning might be violet, though, especially at dusk, so they might conflate the color of the two. SinisterLefty (talk) 02:04, 18 June 2019 (UTC)[reply]

Another factor to consider is our "mental white balance". That is, since we have a yellowish star, we tend to see that as white. If we had a bluish star, we likely would have evolved to see that as white. There's even a quick adjustment to the color. Try on different colored sunglasses, and the scene will seem to be different colors, but if you leave one pair on for a while, that will set the new white balance in your mind. SinisterLefty (talk) 02:22, 18 June 2019 (UTC)[reply]

We don't have a "yellowish star". It's white. As you note, that's essentially where our concept of "white" comes from, but nevertheless that's what it is. It just isn't yellow, period. --Trovatore (talk) 02:28, 18 June 2019 (UTC)[reply]

Our Sun article states that while it's a yellow dwarf, "its light is closer to white than yellow". So, in other words, it has a yellowish tint to it. SinisterLefty (talk) 03:06, 18 June 2019 (UTC)[reply]

Is there a source for that statement? ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:24, 18 June 2019 (UTC)[reply]

I don't see one, but I took it at face value. If that's inaccurate, it should be fixed. SinisterLefty (talk) 03:27, 18 June 2019 (UTC)[reply]

Finding a source, one way or another, would be the best option. Here's one from Stanford.[1] ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:00, 18 June 2019 (UTC)[reply]

I read that as "the Sun is often called a 'yellow dwarf', but it's really white." Out of the visible spectrum, the Sun actually gives off the most light in green. --47.146.63.87 (talk) 06:03, 18 June 2019 (UTC)[reply]

colour is subjective (and contextual), but one way to make it objective is to say that sun color is 5,777 Kelvin. Which translate as this (from black-body radiation), that is, in my eyes, slightly yellowish-white

Gem fr (talk) 07:07, 18 June 2019 (UTC)[reply]

I'm not altogether convinced by that graphic. You're right that 5800 K on that chart hits a yellowish patch (at least on my screen). But even a 5000 K lamp looks, if anything, slightly blue to most people, at least when used for indoor lighting. --Trovatore (talk) 17:54, 18 June 2019 (UTC)[reply]

The confusion may be due to that graphic not being the actual color of those objects, but rather their color "as seen in the night sky", so after passing through the atmosphere, which would diffract some of blues away, giving what remains more of a yellow hue. SinisterLefty (talk) 18:17, 18 June 2019 (UTC)[reply]

~~Rayleigh scattering is a small effect for objects high overhead, not enough to change their color significantly.~~ --Trovatore (talk) 19:26, 18 June 2019 (UTC)[reply]

They didn't specify the angle. SinisterLefty (talk) 19:44, 19 June 2019 (UTC)[reply]

Actually, after visiting that page, I'm no longer so sure it's insignificant. Still, I don't think the OP was asking what color the Sun is when you can comfortably look at it; that's not a question you really need to ask the refdesk. You just go outside and look. --Trovatore (talk) 20:44, 21 June 2019 (UTC)[reply]

Not if they're color-blind. Also, since there's a range of colors, it would take many observations to determine the full range. And it's rare that you can comfortably look at the Sun with the bare eye. There's sunrise and sunset, but it might still be too bright then. There's fog and overcast conditions. And there're certain total eclipses, but that's dangerous as you may suffer eye damage when the Sun peaks out from behind the Moon. Dark sunglasses help, but may also change the color. SinisterLefty (talk) 00:21, 22 June 2019 (UTC)[reply]

The color white is by definition that color that you see when you're outside looking at an object that reflects all wavelengths uniformly. Your brain will adjust the white balance to make it so. Count Iblis (talk) 10:39, 18 June 2019 (UTC)[reply]

White balance has limits. Blood will never look white in full color vision (photopic). What blackbody is furthest from where your visual lobe can't white balance it to look white anymore? That is the whitest white blackbody possible. Now if you could do this in a holodeck and instantly raise the other wavelengths of that perfect blackbody to that of the brightest wavelength (one of the greens I think) wouldn't violet and red objects suddenly look brighter? If the green wavelengths are only 109% the brightness of the violet and red wavelengths in theory they'd get brighter but you'd barely notice if at all. Would objects with equal albedo between the world records of wavelength perception (at least 280-850nm) suddenly become so white they they suddenly look slightly green-tinged when you switch back to blackbody or is a blackbody of the right Kelvins already the whitest white the brain can perceive? Eclipse eyeglasses dim 100,000 times. Since the Sun is best photographed through a telescope at 1/125 to 1/1000 seconds or less to freeze the same effect that makes stars twinkle they make filters for cameras that dim only 10,000 times but those can damage your vision when looked through. If you were at the distance in space where the Sun was 100,000 times dimmer per cone (about 0.005 degrees) or whatever it is that doesn't saturate a cone but still bright enough for full color vision (so still bright by stars in Earth's night standards) then the Sun would look yellowish white (at least if you hold a rainbow of equally bright LEDs from 400 700 nm near it to tell your brain fuck you, stop white balancing) but from Earth it saturates all cones which would make it impossible to see any yellowness even if the brain didn't adjust white balance which it does. As the eye has microsaccades and averages brightnesses on the timescale of the persistence of vision the Sun probably can be more than 1/100,000th the square degrees of a cone cell before cones get saturated. Sagittarian Milky Way (talk) 13:57, 18 June 2019 (UTC)[reply]

Blood is fairly dark (nonreflective), so isn't going to look white, but does sometimes look black, as when viewed in dim light. SinisterLefty (talk) 14:17, 18 June 2019 (UTC)[reply]

Everything looks grayscale if it's dim enough (scotopic, too dark for cones to see anything). Then there's mesopic, rods not saturated yet but cones at the dim end of their scale. Thus blood doesn't look white or gray to the non-colorblind while the gibbous Moon is also fairly nonreflective (no glass bead retroreflection or complete lack of shadow hiding like full moon) and looks white at night when high up cause it's the brightest thing in view (sunlit ground) and close enough to white for the eye to white balance, unlike typical sunsets, blood, oranges, maple leaves, gas flames or monochromatic LEDs. Sagittarian Milky Way (talk) 15:49, 18 June 2019 (UTC)[reply]

FCS, guys, the OP just asked the color of the sun (which is, again, 5,777 Kelvin. Period.). look at your answers... Gem fr (talk) 09:53, 19 June 2019 (UTC)[reply]

The absolute color is certainly relevant, but since the OP is presumably here on Earth, it's reasonable to assume that they may also want to know what color the Sun appears to be on Earth (and they may not realize there's a difference). SinisterLefty (talk) 19:47, 19 June 2019 (UTC)[reply]

The Sun is obviously black, because it is a black body. It is equally obviously white, because it defines the white light we work by naturally on Earth. If you believe your own eyes, you must say it is yellow, since it looks yellow in the sky (unless it's white or orange or green or some other color). Additionally, it is plainly infrared, since this is the predominant frequency at which it irradiates. [2]. Or if you insist on visible light, say that it is red. The same source explains that it is plainly blue, since this is the wavelength it emits at the highest level. Look too long while pondering these things, and you will see no color at all. I think the Sun, as the source of color itself, has the power to create our conceptions of color, and to destroy them. Wnt (talk) 15:55, 28 June 2019 (UTC)[reply]