Wikipedia:Reference desk/Archives/Science/2023 September 2

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September 2

Charles's wain

On Thursday at my local library I picked up a copy of a free newspaper of which I was not previously aware - the EC1 Echo - although I do recall that in 2000 I had a letter published in the Clerkenwell and Finsbury Advertiser, which folded soon after (no pun intended). This is a bi-monthly journal, and reading page 2 this morning I saw from the editorial that the current August-September issue will be the last. The news story, Council aim to increase housing stock: Charles Simmons House will create 25 homes for genuinely affordable rent covered exactly the same issues which I wrote about all those years ago (see m:Talk:IP Editing: Privacy Enhancement and Abuse Mitigation#Converting temporary accounts to permanent, comment 31 July).

At the top of the page there are two black discs 3/8" in diameter connected by a curved row of dots. Above the left hand disc is written 1^st Aug and above the second 30^th Sep. Below the first disc is written "Full Moon 100%/0.55" and below the second "Waning Gibbous 98%/0.54". I can understand the percentages, but what are the decimals referring to? 2A02:C7B:124:3D00:2B8D:308D:B18C:5BD8 (talk) 11:24, 2 September 2023 (UTC)

WAG: albedo? -- 136.54.106.120 (talk) 11:45, 2 September 2023 (UTC)

This suggests it's the moon angle or how much of the sky the moon appears to cover - they are decimal fractios of a degree. Alansplodge (talk) 12:12, 2 September 2023 (UTC)

So it's highest at perigee? —Tamfang (talk) 14:18, 2 September 2023 (UTC)

The angular diameter of the Moon varies between about 29′20″ and 34′6″ (according to our article angular diameter – I saw no two book sources that agree, but most come close to 29½′ – 33½′). So whatever 0.55" and 0.54" stand for, it is not the angular diameter. A full circle is 360° = 21600′ = 1296000″, so you can string more than two million circles with an angular diameter of 0.55″ around the heavenly sphere and the ends will still be far apart.  --Lambiam 15:22, 2 September 2023 (UTC)

The OP (and maybe the newspaper) didn't specify any units — the " is a quotation mark. Since 34′6″ = 0.568° (29′20″ = 0.489°), we're in the right ball park. The two full moons in August were touted as "supermoons" in the press, so that's also plausible. Stellarium gives 0.56° for 1st August. --Wrongfilter (talk) 16:22, 2 September 2023 (UTC)

The Moon can be 34.1' wide but an Earth radius is about a 60th of the Moon distance so it can't be 34 point anything from Earth's center (likely where the naïve 33 and a half came from, directly underneath the Moon will always be very roughly half minute bigger than from the center) Sagittarian Milky Way (talk) 16:44, 2 September 2023 (UTC)

The www.moongiant.com link above gives the "moon angle" for today as 0.54° which seems to concur. Alansplodge (talk) 16:51, 2 September 2023 (UTC)

Also note that perigees have different strengths. Every circa 205.9 days perigees are weak, circa 102.95 days later it's strong and near new or full. With an anomalistic year of 365.259-something days the full supermoon passes perihelion once every 365.259 ÷ (205.9 x 2 - 365.259) = ~8 years and is extra super then (Sun's gravity warping Moon orbit ellipse more at perihelion). Sagittarian Milky Way (talk) 22:44, 2 September 2023 (UTC)

Vertigo and self-preservation

I began to wonder why human organism often respond with balance-threatening vertigo to big heights at the cost of self-preservation? This is seemingly in contrast to responses in other emergency or life-threatening situations that often involve adrenaline rush, increased heartbeat, etc to aid escape and/or overcome the danger. With that in mind, one would expect either universal absence of vertigo among all humans or something opposite, such as grasping reflex. 212.180.235.46 (talk) 19:03, 2 September 2023 (UTC)

Guessing that the negative effects act as a deterrent, discouraging folks from getting into life-threatening situations in the first place. For me, just looking at a photo of somebody in a precariously high situation makes me queezy. E.g. -- 136.54.106.120 (talk) 21:38, 2 September 2023 (UTC)

Makes sense, thanks all. 212.180.235.46 (talk) 07:03, 3 September 2023 (UTC)

Many people do exhibit a grasping reflex in such situations. Anecdotally, firefighters sometimes find a rescued person will just tightly cling to a ladder rather than climb down it. I myself have experienced a similar impulse when on a ladder at first (US: second) floor gutter level. (I too greatly dislike heights, though I don't suffer vertigo.)

That said, I'm not sure that vertigo is a common response to heights – this might be mostly a myth popularised by Alfred Hitchcock's film Vertigo, in which the protagonist suffered from two conditions, vertigo and acrophobia (fear of heights). {The poster formerly known as 87.91.230.195} 51.194.81.165 (talk) 05:13, 3 September 2023 (UTC)

Lower specific energy results in higher power?

Unless I'm misunderstanding/misreading something, these two sentences from the article on nitromethane seem contradictory: "Nitromethane, however, has a lower specific energy: gasoline provides about 42–44 MJ/kg, whereas nitromethane provides only 11.3 MJ/kg. This analysis indicates that nitromethane generates about 2.3 times the power of gasoline when combined with a given amount of oxygen." Is this correct? ZFT (talk) 20:46, 2 September 2023 (UTC)

Burning 1 kg of nitromethane takes less air than burning 1 kg of petrol. The power of an internal combustion engine of particular size and speed is limited by the amount of air it can take in. Therefore, the nitro burning engine can burn fuel much faster than a petrol fuelled one, giving it more power, despite getting less energy per kilogramme of fuel.

BTW, sounds like a terribly polluting fuel. PiusImpavidus (talk) 09:03, 3 September 2023 (UTC)

The calculation on the power produced by nitro fuelled internal combustion engines in that article is marked with . I didn't check the numbers, but it already sounds dubious that it assumes both the nitro and the petrol engine run stoichiometrically, or at the same ratio away from stoichiometry. Later on the article mentions that nitro engines run very fuel-rich, invalidating the above assumption. This gives incomplete combustion, so less energy per kilogramme of fuel, but burns even more fuel for more power. PiusImpavidus (talk) 09:29, 3 September 2023 (UTC)