Wikipedia:Reference desk/Archives/Science/2015 September 19

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September 19

Primitive solar observation

Solar observation discusses the history of the process, but it doesn't explain the mechanics; exceptions such as eclipses can be done with the naked eye (especially since the ancients maybe didn't know that it was still dangerous), but sunspots are radically different. Was the camera obscura typically used by the early observers of sunspots, or was there some other technique, or do we not know? Nyttend (talk) 00:19, 19 September 2015 (UTC)

Sunspots were not observed until the invention of the telescope. As solar observation explains, the Fabricii used a combination of telescope and camera obscura, and there were conflicting claims of priority in discovery because, as soon as the telescope came into astronomical use, multiple observers saw the sunspots. While looking at the Sun with the naked eye poses some risk, and is strongly discouraged, looking at the Sun with a telescope is more dangerous, and it is probably his observations of the Sun with the telescope that caused Galileo to become blind. Robert McClenon (talk) 02:32, 19 September 2015 (UTC)

(edit conflict) Sunspots were not systematically recorded until the invention of the telescope. The Chinese observed sunspots long before the invention of the telescope; see e.g., here. Short Brigade Harvester Boris (talk) 02:43, 19 September 2015 (UTC)

Note that a pinhole lens and white projection surface alone is enough to observe the Sun. That is, you don't need a darkened chamber, since the Sun was so much brighter than everything else on Earth then, so extraneous light doesn't much matter. Also, somebody with diminished vision, such as from cataracts, might have been able to look directly at the Sun and make out large sunspots. (Not good for the eyes, I'm sure, but if they were going blind anyway they might have risked it.) Also, just the right thickness of clouds might work (especially at dawn and dusk, where the sunlight travels through a lot more air to reach you), although there's a big risk that you would damage your eyes when the clouds thin out. And if they had the technology to make glass, then a semi-transparent glass could dim the Sun enough to look directly at it, too. Even the reflection of the Sun on still water might be darkened enough.StuRat (talk) 02:41, 19 September 2015 (UTC)

sole hair

Is it ever possible for hair to grow out of the bottom of a human’s foot? --Romanophile (talk) 02:53, 19 September 2015 (UTC)

Hypertrichosis is our article on excessive hair growth, and it mentions types that do NOT effect the soles of the feet. One type does say it affects all areas of the body, but doesn't specifically say the soles: "Congenital terminal hypertrichosis is characterized by the presence of fully pigmented terminal hair that covers the entire body". StuRat (talk) 03:03, 19 September 2015 (UTC)

Hair growth on the foot sole is possible by deliberate Hair transplantation or by a rare skin disorder Palmoplantar keratoderma - see Carvajal syndrome "Striate palmoplantar keratoderma with woolly hair and cardiomyopathy" with references cited in the article. 84.209.89.214 (talk) 10:55, 19 September 2015 (UTC)

The palms and soles of primates, and really any typical mammal, tends to be hair-free. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:25, 19 September 2015 (UTC)

If I'm not mistaken, that's pretty much why OP is asking... Dismas|^(talk) 04:36, 20 September 2015 (UTC)

A google search on the subjects of both hair and suntanning on the palms and soles pretty much yields the same conclusion: The skin on the palms and soles is thicker than elsewhere, and does not have hair follicles or melanin. Hence, no hair, and no suntanning. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:32, 20 September 2015 (UTC)

Estuarine narrowing

What causes artificial narrowing of estuaries around bridges? — Preceding unsigned comment added by 2A02:C7D:B917:9700:850B:FA4A:43FF:94ED (talk) 09:52, 19 September 2015 (UTC)

See Bridge scour. Tevildo (talk) 10:01, 19 September 2015 (UTC)

I have read that but it doesn't answer my question. — Preceding unsigned comment added by 2A02:C7D:B917:9700:850B:FA4A:43FF:94ED (talk) 10:04, 19 September 2015 (UTC)

artificial adj. means caused or created as a result of human influence or action. Do you have an example of a bridge crossing of an estuary that has narrowed after the bridge crossing point was chosen? 84.209.89.214 (talk) 12:00, 19 September 2015 (UTC)

A valid point if we take the OP's question literally - the thing that causes artificial narrowing is a civil engineer. As far as scour is concerned; the water flows more quickly around the bridge piers than in the main stream of the river. This causes material to be removed from the riverbed near the piers, and deposited towards the centre of the river, causing the channel to narrow (and, in some cases, the bridge to collapse). This information is in the bridge scour article, honestly. Tevildo (talk) 14:05, 19 September 2015 (UTC)

Are you talking about putting artifical land before the bridge built to make the channel narrower and easier to span in a single span?

Another possible effect is if they reinforced the banks to prevent erosion that might cause the bridge supports to collapse. This would then prevent erosion there, while the rest of the river might erode and widen (some rivers naturally widen while others naturally narrow). Thus, it would appear that the river had narrowed by the bridge, when in fact it widened everywhere else. StuRat (talk) 15:18, 19 September 2015 (UTC)