Today I Learned

[BillTre]

Today I Learned this exists:

Might be a surprise for anyone on the porch.

 

[berkeman]

Or porch pirates!

 

[hilbert2]

https://phys.org/news/2020-09-astronomers-earth-sized-pi-planet-day.html

But is it 3.14 Earth days or 3.14 times its own day? If the latter, then any alien intelligent being would notice this curious fact, too.

 

[mfb]

Our days. Rotation periods are very difficult to measure and astronomers wouldn't write days then.

 

[hilbert2]

Our days. Rotation periods are very difficult to measure and astronomers wouldn't write days then.

Yeah, I understood that it's almost certainly Earth days. And a planet orbiting a star that close to it is usually tidally locked, as far as I know (not being a specialist in this).

 

[BillTre]

Another weird 2020 thing:
Today I learned 2020 now has a Zombie Tropical Storm.

Zombie tropical storms are when a tropical storm becomes weak, drops out of thee tropical storm category due to its loss of strength, but then gets stronger and becomes a tropical storm again.

 

[Swamp Thing]

Today I learned that vanilla is an orchid -- the only edible orchid, actually.

 

[collinsmark]

https://phys.org/news/2020-09-astronomers-earth-sized-pi-planet-day.html

But is it 3.14 Earth days or 3.14 times its own day? If the latter, then any alien intelligent being would notice this curious fact, too.

Our days. Rotation periods are very difficult to measure and astronomers wouldn't write days then.

Yeah, I understood that it's almost certainly Earth days. And a planet orbiting a star that close to it is usually tidally locked, as far as I know (not being a specialist in this).

We can do the math to see if it's at least in the ballpark!

The key sentences are:

It orbits a cool, low-mass star that is about one-fifth the size of the sun. The planet circles its star every 3.14 days, at a blistering 81 kilometers per second, or about 181,000 miles per hour.

That all the info one needs to calculate the period. The following equations could prove useful:

Centripetal force equals gravitational force (assuming a circular orbit):

$\frac{v^2}{r} = G \frac{M}{r^2}$

We're not given what $r$ is. But we're not looking for $r$, we're looking for the period $T$. And we know

$v = \frac{2 \pi r}{T}$

Solve for $T$. According to my calculations, if $M$ is just a bit lighter than $\frac{1}{5}$ the mass of the Sun, the period is at least somewhere in the ballpark of the claimed 3.14 Earth days.

 

[hilbert2]

Found something to compare this to:

The exoplanet Gliese 581b has a mass of 15.8 times Earth and its orbital period is about 5.4 Earth days. The orbit radius is 0.041 AU, much less than even that of Mercury. The next closest planet orbiting that star, Gliese 581c, is said to be almost certainly tidally locked because even it is so close to the star. I'm not sure if the 581b is a gas planet and whether that prevents tidal locking, but otherwise it should be tuned to rotate in that way too.

 

[Keith_McClary]

TIL

 

[mfb]

I didn't learn it today, but I never saw the connection until today:

In English, if you don't care about something you can say you don't give a sh*t.
In German, if you don't care about something you can say "Scheiss drauf", which translates literally to "sh*t on it".

Same meaning, completely opposite phrase.

 

[Tom.G]

TIL a new word, "abseiling."
Used by @Astronuc in post:
https://www.physicsforums.com/posts/6400047/

Google says; British: ... descending a rock face or other near-vertical surface by using a doubled rope coiled round the body and fixed at a higher point.

 

[Astronuc]

TIL a new word, "abseiling."
Used by @Astronuc in post:
https://www.physicsforums.com/posts/6400047/

Google says; British: ... descending a rock face or other near-vertical surface by using a doubled rope coiled round the body and fixed at a higher point.

It was new to me too, since I don't rappel or rope climb very often. The word is derived from German verb abseilen, to rope down, or lower by rope, or rappel. One can also use 'sich abseilen'.

https://en.wikipedia.org/wiki/Abseiling

 

[DrGreg]

It was new to me too, since I don't rappel or rope climb very often. The word is derived from German verb abseilen, to rope down, or lower by rope, or rappel. One can also use 'sich abseilen'.

TIL a new word "rappel". It means "abseil".

Strange how some words don't travel. "Abseil" is well-known (to the general public) in the UK, but "rappel" isn't.

 

[Astronuc]

TIL a new word "rappel". It means "abseil".

Strange how some words don't travel. "Abseil" is well-known (to the general public) in the UK, but "rappel" isn't.

When I saw the word, I figured that it must have German origin. Rappel has a French origin.

https://www.etymonline.com/word/rappel
https://en.wikipedia.org/wiki/Australian_rappel

I was also surprised by the note on the Wikipedia page about Abseiling: "This article may lend undue weight to certain ideas, incidents, or controversies." Seriously?!

I would have thought Aussie rappelling, or abseiling, would be doing it upside down.

 

[fresh_42]

TIL a new word, "abseiling."
Used by @Astronuc in post:
https://www.physicsforums.com/posts/6400047/

Google says; British: ... descending a rock face or other near-vertical surface by using a doubled rope coiled round the body and fixed at a higher point.

The German word is "abseilen". ab for down and seil for rope. We also use it if we want to leave a place secretly, e.g. leaving a party or meeting early, in which case it is used reflexive: sich abseilen = to abseil oneself.

 

[DrGreg]

https://en.wikipedia.org/wiki/Australian_rappel

I would have thought Aussie rappelling, or abseiling, would be doing it upside down.

I've just read the Wikipedia article, and they do do it upside down, i.e. facing downwards and away from the rock face or building, the opposite of what I understood as "abseiling".

 

[Astronuc]

We also use it if we want to leave a place secretly, e.g. leaving a party or meeting early, in which case it is used reflexive: sich abseilen = to abseil oneself.

As opposed to "sich aufseilen" = to pull oneself up by rope?

 

[fresh_42]

As opposed to "sich aufseilen" = to pull oneself up by rope?

Never heard before, but it's in the dictionary.

 

[mfb]

I was also surprised by the note on the Wikipedia page about Abseiling: "This article may lend undue weight to certain ideas, incidents, or controversies." Seriously?!

Here is the explanation. The user who added that template argues that rappelling is more widely used and should be preferred.

I never heard "aufseilen" before either.

 

[fresh_42]

I never heard "aufseilen" before either.

I suppose neither of us knows some of these guys:

 

[Ibix]

Some cichlids eat the scales off of other cichlids as a major nutritional component. They have a handedness to their mouth so they specialize in eating scales from one side of their prey.

Today I learned that there are asymmetric fish that specialise in eating from one side of their prey.

 

[BillTre]

Here's another weird one: Anableps

They are asymmetrical in their sexual organs: they are live bearers (don't lay eggs, give birth to little fish) and therefore require internal fertilization.
The male has a specialized fin which acts like a penis to transfer sperm, as required for internal fertilization.
In Anableps, their body geometry (presumably, their more round in cross section then many other live bearers) drives the specialization of mating from one side or the other, but not both.

Additionally, they are known as "four eye fish" because each of their two eyes are divided horizontally.
Each different properties; one for looking under water (like normal fish), one for looking through the air from their poked out of the water position, for threats from above.
These fish live in shallow brackish water shores, like beaches/mudflats.
They are prey for birds flying over, so they have to aware of them --> in order to, through intentional movement, avoid predation.
They seem to be constantly in rapid motion.

They will go under water, but prefer to be at the top with their eyes poking out.

 

[Keith_McClary]

TIL about bilateral gynandromorphy in Pheucticus ludovicianus

while one side of the rose-breasted grosbeak appears genetically female, the other side shows all the hallmarks of a genetic male.

 

[ishika17]

Today I learned about amazing facts that Green Chemistry is resulting in.and It is actually turning Oranges to plastic!
http://advancinggreenchemistry.org/... explained in,the carbon dioxide they produce.

 

[hilbert2]

You can make a tube lamp light up a bit by taking the voltage from several 9 V batteries connected in series, but you probably don't want to combine enough batteries to equal the intended voltage.

 

[Tom.G]

...several 9 V batteries connected in series...

Please define or approximate "several."

 

[hilbert2]

Please define or approximate "several."

Even one battery will make it produce some light, two or three a bit more.

 

[Swamp Thing]

but you probably don't want to combine enough batteries to equal the intended voltage.

You could always put a resistor in series.

Would about 50 volts be enough to see some glow? If so, you could safely let the current pass through you from fingertip to fingertip. (Umm, maybe not if you have any kind of heart condition). Or, you and a couple of friends could join hands to form the circuit... a modern version of those 18th century electrostatic parlor tricks.

You could even combine it with some Victorian occultism and, ah, "conduct" an electric séance.

 

[Keith_McClary]

You can make a tube lamp light up a bit by taking the voltage from several 9 V batteries connected in series

This page suggests you need hundreds of volts if you don't preheat the electrodes.

There is an LED replacement.

 

[mfb]

Would about 50 volts be enough to see some glow? If so, you could safely let the current pass through you from fingertip to fingertip.

• Not advisable in terms of safety
• it would limit the current so much that you won't see anything.

 

[hilbert2]

This page suggests you need hundreds of volts if you don't preheat the electrodes.

There is an LED replacement.

As far as I know, the longer bathroom tube lamps often have this kind of "igniter" at one end to start the current flow.

 

[Tom.G]

Since that is a 2-pin device it is called a Starter (in the US), it is a Normally Closed thermal switch that connects power to the filaments (heaters) in the tube. This vaporizes some of the Mercury in the tube, which is the main conductor during operation.

After a few seconds, the Starter heats up enough to open, removing power from the filaments and applying the high voltage across the ends of the lamp. The high voltage is sufficient to ionize the the Mercury vapor and other gasses in the tube to a plasma, thus emitting UltraViolet light.

The UV light excites the phosphors coating the inside surface of the tube to emit visible light. Different combinations of phosphors are used for different Color Temperatures such as Warm White, Cool White, Daylight, etc.

There are also Instant Start lamps and circuits that do not need a Starter or an Ignitor.

Cheers,
Tom

 

[etotheipi]

TIL that the empty set $\varnothing$ is a function!

 

[DaveE]

TIL: A Butt is (ok, was) a real unit of measure. 1 Butt ≈ 500 litres of wine. So drinking a Butt-load of wine probably isn't a great idea.