Today I Learned

[jim hardy]

The one I took out of a 3/8 black and decker drill seems to be a 3/16-32 screw, which is a size I have never heard of before. I get a diameter of .186 and 32 TPI.

That seems within tolerance for a 10-32. It an be as small as 0.184 and still meet class 3.
http://www.engineersedge.com/screw_threads_chart.htm

0.1861 would be smack in the middle of grade 2.

from http://www.engineersedge.com/thread_strength/thread_classes.htm

old jim

 

[zoobyshoe]

That seems within tolerance for a 10-32.

Of course. I don't know why I dismissed that. A left handed 10-32 screw might be easier to find than a left handed 3/16-32, heh heh.

 

[jim hardy]

Of course. I don't know why I dismissed that. A left handed 10-32 screw might be easier to find than a left handed 3/16-32, heh heh.

With my luck it'd be Whitworth threads - same pitch but 55 degrees...

 

[Bystander]

TIL that endarterectomies are not fun.

 

[Borg]

TIL that endarterectomies are not fun.

That certainly doesn't sound like fun. Hope you're doing better.

 

[jtbell]

Today I learned that "stressed" spelled backwards is "desserts." Our college's dining hall had a special dessert bar set up today for final exam week.

 

[wolram]

Today i learned that costalota means taking two women shopping.

 

[Borg]

Today i learned that costalota means taking two women shopping.

Is that something like Ménage à cash?

 

[OmCheeto]

Last week, I noticed that my fish made a baby.
Being egg layers, I assumed there were more babies. I've counted about a dozen so far.
But in my searches, I noticed some tiny little "Hydra" looking creatures.

​

No big deal.

But I googled "Hydra", and discovered that, they are immortal. [ref wiki]

I didn't know such creatures existed.

 

[Cruz Martinez]

Today i learned that a trivial topological space is pseudo-metrizable.

 

[Silicon Waffle]

Ewww, the white fish...

 

[Lisa!]

TIRT I'm mainly on my silent mode these days!

 

[Hornbein]

Today I learned that the Earth's axis precesses because the Earth is oblate.

 

[Evo]

Zooby's "how-to-tell-if-a-transistor-is-npn or pnp" has been moved to "https://www.physicsforums.com/threads/how-to-tell-if-a-transistor-is-npn-or-pnp.847755/ as it's own thread now.

 

[baudrunner]

Today I learned that a parsec is 3.262 light years long, and that the total number of possible 6 number combinations from the range of 1 to 39 inclusive are 3.262 million.

 

[Hornbein]

Today I learned that James Clerk Maxwell was the first to project a color image using the red-green-blue system.

I also learned that a few people can see a fourth color, so RGB is inadequate for them. One of these said the world of man was full of clashing colors, and that supermarkets were the worst.

 

[Lisa!]

TILT my problems with the boss might be side effects of the medication that I'm taking!
But that doesn't change the fact that she's really annoying and it's hard for everyone to stand her.

 

[jim hardy]

TIL how to re-attach the back of a violin using 'hide glue' .

 

[Ibix]

TIL how to make chicken jalfrezi in a slow cooker. A hint if you try it: don't be in the house smelling the lovely spicy cooking smell for six hours. I felt like one of Pavlov's dogs...

 

[Silicon Waffle]

TIL about drought tolerant plants (good GMO ) which help dry farmers to cope with water shortages.

 

[Borg]

TIL that there was a Star Wars Holiday Special in 1978.

George Lucas himself disliked the special and reportedly said, "If I had the time and a sledgehammer, I would track down every copy of that show and smash it.

I'm guessing that it wasn't very good.

 

[mfb]

TIL how ridiculously windows 10 handles local networks. If a network exists, you are not allowed to make a new one, you either have to join the existing one or remove all computers from the existing one to get rid of the old one. You don't know the password? You need the computer that made the network to look it up. That computer does not exist or does not work any more, but the other computers still know it existed and created the network once? Bad luck.

 

[Fjarkonnun]

Today I learned some things about XML; specifically, what XML is used for, how it is different from HTML, what it was based on (SGML). I learned about XHTML.

On a meta level, I (re)learned how I can learn better; to set a specific goal and go to another room to work on it. I will do that every day from now. It's very fulfilling.

 

[Dishsoap]

Today I learned that if you forget to add salt to your cookies, they won't rise!

 

[tfr000]

Today I learned that the Higgins Armory Museum closed a couple of years ago!
Probably the coolest museum I have ever had the pleasure of wandering through...
http://www.higgins.org/
https://www.google.com/search?q=hig...mP9vrJAhUCUD4KHQoBCJcQsAQIPg&biw=1366&bih=669

 

[NascentOxygen]

Today I learned that if you forget to add salt to your cookies, they won't rise!

I think you may be misapportioning blame here. NaCl plays, at best, a minor part in the rising.

Apart from flour and flavourings, what other ingredients does your recipe call for? http://www.imageshack.com/a/img109/4666/holly1756.gif

 

[Silicon Waffle]

TIL about the X in Xmas, it stems from Χριστός (no idea how to pronounce this word) which means Christ.

 

[Bystander]

"Ch-r-i-s-t-o-s."

 

[zoobyshoe]

Today I learned that part of the pressure on politicians to end Prohibition came from people who argued that opening breweries would create jobs and help counterbalance the economic depression.

 

[Silicon Waffle]

TIL a new English phase "escape one's ancient root", that sounds a little strange to me as I have never used it myself before (I have only one root to grow from, a directed tree.)

 

[Jonathan Scott]

TIL a new English phase "escape one's ancient root", that sounds a little strange to me as I have never used it myself before (I have only one root to grow from, a directed tree.)

I'm familiar with the phrase "escape one's roots", which has the double implication of wanting to escape from one's original background but at the same time suggesting that this might be as difficult as a plant trying to move away from its roots. I've not heard a variant with "ancient root" instead of "roots".

 

[zoobyshoe]

Wow.
------------

 

[zoobyshoe]

Today I learned:

In 2012, on the 35th anniversary of the Wow! signal, Arecibo Observatory beamed a response from humanity, containing 10,000 Twitter messages, in the direction from which the signal originated.

 

[OCR]

Yeah, it was a "Wow" ! ...

​

Arecibo scientists have attempted to increase the chances of intelligent life receiving and decoding the celebrity videos and crowd-sourced tweets by attaching a repeating sequence header to each message that will let the recipient know that the messages are intentional and from another intelligent life form.

Well dang... that screwed that, then...

 

[zoobyshoe]

Well ****... that screwed that, then...

As Sagan highlighted, our TV signals have been going out for decades. So, there wasn't much intergalactic reputation left to salvage.

 

[DiracPool]

As Sagan highlighted, our TV signals have been going out for decades. So, there wasn't much intergalactic reputation left to salvage.

Wasn't it cool how the extra-terrestrials just happened to catch the first TV signals from the Berlin games and respond so promptly?

 

[Boolean Boogey]

I really like the movie Contact.

 

[collinsmark]

Today I learned that every natural number (positive integer) r is the inradius of a right triangle whose sides are:
a = 2r + 1
b = 2r^2 + 2r
c = 2r^2 + 2r + 1

And since r is a natural number (positive integer), a, b and c are also natural numbers (positive integers). And since b and c differ by only 1, the triangle represents a primitive Pythagorean triple.

In other words, every natural number is associated with a primitive Pythagorean triple (and might be the inradius of many Pythagorean triples, but there will always be at least one, and that one will be primitive).

[Edit: and by extension, that implies that there are infinitely many primitive Pythagorean triples.]

 

[Hornbein]

Today I learned that every natural number (positive integer) r is the inradius of a right triangle whose sides are:
a = 2r + 1
b = 2r^2 + 2r
c = 2r^2 + 2r + 1

And since r is a natural number (positive integer), a, b and c are also natural numbers (positive integers). And since b and c differ by only 1, the triangle represents a primitive Pythagorean triple.

In other words, every natural number is associated with a primitive Pythagorean triple (and might be the inradius of many Pythagorean triples, but there will always be at least one, and that one will be primitive).

[Edit: and by extension, that implies that there are infinitely many primitive Pythagorean triples.]

I have read that this was known in ancient Babylonia. There is a list of Pythagorean triples on a clay tablet. https://en.wikipedia.org/wiki/Plimpton_322

 

[Borg]

Me: TIL a very classic moral lesson in life about one's selfishness which is the cause for a lot of troubles. I think troubles are naturally implemented as an endless linked list data structure, the head of the first element points to nothing but its tail point to the next element's head, on and on with next and next elements. The last one's tail is pointing to Null,Zero or Nothing.

And yet, many people spend their lives chasing their own tail.

 

[OmCheeto]

Some days I learn just a few things. Some days I learn a thousand things.
Today was one of those "thousand things" days.
To keep it short, I'll only share what I consider "strangest":

The Earth's atmosphere has permanent, thin layers of iron and sodium, about 60 miles above the surface.
Kind of like Earth encompassing, gaseous metallic Dyson spheres.​

Random brief description: METALLIC VAPOR LAYERS [albany.edu]

I have no idea how it works.

I learned this, at the end of an endless stream of searches, trying to find out why the lightsaber battles on Mauna Kea, were yellow.

 

[mfb]

Well, there is a layer where a few metal atoms exist. The main components of the atmosphere are still the same everywhere.

 

[OmCheeto]

Well, there is a layer where a few metal atoms exist. The main components of the atmosphere are still the same everywhere.

Those metal atoms sure put off a significant yellow glow, for being just a few.

per wiki; "The density varies with season; the average column density is roughly 4 billion sodium atoms/cm³."

for comparison

...gas on Earth
typical atmosphere = 2.7 x 10¹⁹/cm³
best "vacuum" achieved in lab on Earth = 10⁴/cm³

[ref uoregon.edu]

 

[mfb]

10¹⁹/cm³ left at 60 km. That gives a fraction of 0.00000004% or 0.4 ppb sodium. That is below the man-made concentration of chlorofluorocarbon, for example (source), but this CFC concentration is maintained even at lower altitudes with a much higher atmospheric pressure.

 

[jim hardy]

i looked but didn't find how much sodium in solar wind.

 

[Hornbein]

In 2000 someone made a synthetic geodynamo out of a cylinder of rotating liquid sodium.

 

[Ibix]

I learned this, at the end of an endless stream of searches, trying to find out why the lightsaber battles on Mauna Kea, were yellow.

I understand that they don't look that cool in reality, sadly (that's probably a very long exposure shot). But the sodium D-line (589.3nm) is fairly near the middle of the optical spectrum, which is convenient, and is nice and monochrome so it's easy to filter the guide star out of your astronomical images.

 

[OmCheeto]

i looked but didn't find how much sodium in solar wind.

It comes from meteorites.

http://meteorites.wustl.edu/metcomp/nak.htm
https://en.wikipedia.org/wiki/Sodium_layer

I just find it strange that sodium and iron would form stable layers so high up in the atmosphere.
I've seen helium, hydrogen, and hot air balloons go up, but never sodium nor iron filled balloons.
Though, there is a "Led Zeppelin", so I guess it's not completely out of the question.

I understand that they don't look that cool in reality, sadly (that's probably a very long exposure shot). But the sodium D-line (589.3nm) is fairly near the middle of the optical spectrum, which is convenient, and is nice and monochrome so it's easy to filter the guide star out of your astronomical images.

Re-watching the time-lapse of the telescopes and lasers, I'm inclined now to agree, that they are probably very dim.


I really enjoyed reading about why they used the lasers.
Some REALLY interesting facts and figures:

$4 Million Laser Marks Ground Zero for Adaptive Optics Science
...

The adaptive optics system uses this artificial laser guide star to measure the aberrations introduced by turbulence in the earth’s atmosphere. A six-inch diameter deformable mirror with 349 actuators is then used to correct for these aberrations at a rate of 1,000 times per second, effectively taking the twinkle out of the stars and providing near-perfect detail for planets, stars and galaxies. Combined with the 10-meter diameter primary mirror, Keck Observatory can offer images with five times the resolution of even the Hubble Space Telescope.​

 

[Hornbein]

Today I learned that the bigwigs of the early Nazi party invested a million or so marks into the work of an alchemist named Franz Tausend. Tausand was an expert fraud who could produce gold even under stringent supervision.

http://www.kfvr.de/_Media/franz_tausend_med.jpeg
Franz Tausend

 

[fresh_42]

Today I learned that the bigwigs of the early Nazi party invested a million or so marks into the work of an alchemist named Franz Tausend. Tausand was an expert fraud who could produce gold even under stringent supervision.

He died in jail. However $^{197}Hg$ decays to gold