Wikipedia:Reference desk/Archives/Science/2020 December 17

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December 17

Tubes in the human body that are not vital for human life?

Which cases are there of tubes in the human body other than the epididymis and vas deferens that are not vital for human life? The ureter would not be such a tube since the human body cannot actually survive with both ureters being removed but can in fact survive with both vas deferenses being removed and with both epididymises being removed. Futurist110 (talk) 01:39, 17 December 2020 (UTC)

Eustachian tube? You could survive without it, but problems would arise. 2603:6081:1C00:1187:9907:139E:459:8414 (talk) 02:26, 17 December 2020 (UTC)

Fallopian tubes as well, but they are related to the vas deferens. LongHairedFop (talk) 09:35, 17 December 2020 (UTC)

The absence of vasa deferentia or fallopian tubes is not life-threatening to an individual, but their species-wide absence would lead to extinction. Is the nasolacrimal canal a tube? I think it is not vital.  --Lambiam 10:45, 17 December 2020 (UTC)

Humans can reproduce without either an epididymis or a vas deferens through artificial insemination, testicular sperm extraction, and/or IVF. If anything, IVF plus embryo selection could become the preferred reproductive method in the future due to it resulting in offspring with better genes on average. Futurist110 (talk) 21:22, 17 December 2020 (UTC)

• Many individual blood vessels are not, on their own, vital for life. The fact that some random blood vessel in your thigh can be removed and not kill you is why they can be used as grafts in vascular bypass surgery. As noted, however, by Lambiam, how you define human life in the context of the question matters. Humanity goes on if you removed an individual blood vessel from everyone. If you removed everyone's vas deferens, humanity ceases to be alive in a century or so. --Jayron32 19:20, 17 December 2020 (UTC)

Your last sentence here isn't necessarily going to be true if artificial insemination, testicular (and/or epididymal, if one actually keeps one or both epididymis) sperm extraction, and/or IVF (possibly plus embryo selection for desirable traits/genes, which produces better offspring anyway) are going to be used by the population on an extremely massive scale.

I will grant that your statement might have been true in the past when such technologies did not exist, but your statement certainly isn't true right now. Futurist110 (talk) 02:45, 18 December 2020 (UTC)

Saturnalia

Last night Lynn Parsons, one of the Magic radio presenters, said "On 21 December, the winter solstice, Jupiter and Saturn cross paths for the first time in 800 years. I'll talk about this more on Monday." I did some calculations using the books to hand:

On 12 December 1983 Jupiter's mean longitude was 266.8775 degrees. It's mean daily motion is 0.083114722 degrees (calculated from a comparison with its mean longitude 360 days before). On the same date Saturn's mean longitude was 213.6198 degrees and its mean daily motion is 0.033609167 degrees. On Monday, 13,524 days later Jupiter's mean longitude will be 310.9210 degrees and Saturn's will be 308.1502 degrees. They will thus be some 40 degrees east of the sun - they had already set. The difference in daily motion is 0.079753805 degrees, which means the planets will encounter each other (as viewed from earth) every 4513.891218 days, or every 12.35862458 years. So my question is, how close are they going to be on Monday and how close were they 800 years ago? There was supposed to be a big conjunction in 7 BC, 2026 years ago. 2026 years are 163.9341002 conjunction periods, putting the event in February/March of 7 BC. There was another "great conjunction" shortly before the birth of Muhammad. He was born on Monday, 2 June AD 570, 1,450 years ago. 1,450 years is 117.326972 conjunction periods, putting the event in August AD 562. Neither of the books to hand, The Sealed Nectar and Encyclopaedia Britannica, mentions it. 86.166.32.118 (talk) 11:04, 17 December 2020 (UTC)

Something on this at Great conjunction, and they say the period is 20 years - I'll have to revisit my calculation. 86.166.32.118 (talk) 11:13, 17 December 2020 (UTC)

I see from this [1] she is referring to March 1226. 86.166.32.118 (talk) 11:29, 17 December 2020 (UTC)

Silly error - I subtracted 0.003360917 instead of 0.033609167. The difference in daily motions is 0.049505555 degrees and they will catch up every twenty years. I'm re-working the whole thing. 86.166.32.118 (talk) 12:00, 17 December 2020 (UTC)

You will never get exact dates from mean motions as Earth is not at the center of the orbits and the orbits are ellipses. Also you are calculating mean motion wrong, you divide 360 degrees by the length of planet year in days (I would not use planet year lists that do not show Earth as 365.256(363) days (sidereal year), it's the "real" year and using the 365.2422 day terrestrial summer-winter recurrence year that's adjusted for precession just adds complications for no reason, if you see lists of mean motion or planet year lengths from an astrologer it'll likely correspond to this 365.2422 days for Earth year that's shorter than the actual amount of time the planets need to orbit). Subtract the smaller mean motion from the bigger and you get the mean 1-dimensional closing speed in degrees per day. Divide 360 by this and you get the average number of days between great conjunction seasons (occasionally there's 3 great conjunctions a few months apart) which is totally useless for calculating exact dates. Planet speeds oscillate wildly as they undergo cycles of apparent retrograde motion and non-retrograde motion and traverse their elliptical orbit. Sagittarian Milky Way (talk) 16:48, 17 December 2020 (UTC)

I really have to point out that the two planets will not "cross paths" at all. HiLo48 (talk) 21:18, 17 December 2020 (UTC)

What do you mean? That is called an occultation. Extremely rare, I think we have only like 1 or 2 instances with firsthand accounts. That is not a collision because reality is 3D. On the other hand in 1-dimension (forwards and backwards) a planet pair crosses each other all the time, like monthly (average), passing as much as a fist at arm's length apart. Sagittarian Milky Way (talk) 21:47, 17 December 2020 (UTC)

Lynn Parsons was quoted as having said that Jupiter and Saturn will "cross paths". But, as HiLo48 points out, they'll hardly be strangers passing in the night. The planets will still be separated by a spatial distance of some 40 light minutes.  --Lambiam 22:06, 17 December 2020 (UTC)

Depends on what you mean by "planets". If you mean "physical objects orbiting the sun", then their paths (aka orbits) remain separated by the distance you quoted. If you are referring to the "visual phenomenon in the night sky", then their paths of motion do cross. This older definition is often implied when discussing star-gazing, even if "everybody knows" what is really going on. --Khajidha (talk) 01:46, 18 December 2020 (UTC)

I live kind of close to the flight path between Melbourne and Sydney in Australia, one of the busiest routes in the world in normal times, but a long way from the airport, so planes are still at 10,000 to 20,000 feet when they pass overhead. Does that mean the planes and I cross paths every day? HiLo48 (talk) 22:34, 18 December 2020 (UTC)

Stargazing is less 3D than aviation unless you're in a starship. We even still talk about the celestial sphere even if we're science geeks and not geocentrist astrologers. I suspect the astronomers currently studying anything where the 3Dness is more in your face picture everything in 3D more often. Sagittarian Milky Way (talk) 22:52, 18 December 2020 (UTC)

Yes, your paths cross. But they do not intersect. Or do you not agree that a road carried by a bridge that passes over another road "crosses" it?--Khajidha (talk) 00:31, 19 December 2020 (UTC)

Because the Earth (our point of view) moves around and the planets do not orbit the Sun with a constant angular velocity, the exact time between successive conjunctions varies, but the average time ΔT_conj can easily be computed from the orbital periods T_♃ = 4332.59d and T_♄ = 10759.22d using the formula ΔT_conj⁻¹ = T_♃⁻¹ − T_♄⁻¹. This gives us

ΔT_conj = 7253.46d = 19.8585y.

Computing the angular separation on the celestial sphere at the closest proximation during conjunctions is much more complicated; next to the non-uniform motions of the three planets involved, you also have take the angles between their orbital planes into account, for example.  --Lambiam 22:06, 17 December 2020 (UTC)

Yes astronomia el mucho complexo. And sure you don't actually need the degrees, you just want the days for 1 circulation (net) so might as well just measure speeds in "orbits per day". Sagittarian Milky Way (talk) 22:53, 17 December 2020 (UTC)

If you just want a list here's one, if it says conjunction in longitude any approach distances and times will be more accurate than conjunction in right ascension (R.A.) lists but slight differences will remain unless it says closest approach. If you really want to be accurate you could use software to account for parallax but that's more important for planets closer to Earth. Your position relative to the Earth center can only move things around by about how big the Earth would look at the planet's distance and Jupiter is 11 times the width of Earth and Saturn's A rings are about 22 times the width of Earth so yeah it won't matter much. Sagittarian Milky Way (talk) 22:01, 17 December 2020 (UTC)

There was a great conjunction in longitude August 30, 571 AD modern Saudi Time Zone and older Makkah mean and apparent local time but not 570 AD. They were 2.1 minutes of arc apart in 1226 and will be 6.1 in 2020.Sagittarian Milky Way (talk) 23:38, 17 December 2020 (UTC)

Do you mean seconds of arc apart?^[2] Sí, la astronomía es muy complicada.  --Lambiam 07:54, 18 December 2020 (UTC)

No. Seis segundos es ocultación. Sagittarian Milky Way (talk) 09:12, 18 December 2020 (UTC)

Is there a coronavirus tracker tracker? "tracker tracker" doesn't Google well

Excess deaths will of course be higher than confirmed and among the rest of the reputable trackers numbers differ moderately from a number of things like edge cases and what UTC to start counting from, is there a tracker tracker? Who's methodologies cause them to be outliers most often? (in either daily, weekly or total deaths). Also is there a how close America is to running out of ventilators tracker? Ventilator capacity shows a lot of papers for me but no trackers. Will they shift ventilators across the country to avoid needlessly early local shortages? How many ventilators a day can Americans acquire from producers if that happens? Sagittarian Milky Way (talk) 21:33, 17 December 2020 (UTC)

If there is, someone ought to make a tracker tracker tracker... 93.136.217.60 (talk) 16:46, 21 December 2020 (UTC)

Need multiple noninterchangeable trackers of corona trackers to exist first. Wanna start the first tracker tracker? Sagittarian Milky Way (talk) 17:01, 21 December 2020 (UTC)