TIL - Today I Learned .. share something you learned for the first time

[Silent Mistwalker]

24 minutes ago, Madelaine McMasters said:

A shadow is a difference in the brightness of light falling on a surface, caused by something between the surface and the light source. To science, it doesn't matter whether that something absorbs, refracts, diffracts, scatters, or reflects the light, and it doesn't matter whether that difference in brightness is detectable by the human eye. Most of us are only familiar with what we can sense directly under nominal conditions. Everything you said is correct, and fully consistent with the definition of "shadow". If I shine a bright enough light on shadow of an object, it will seem to vanish. That doesn't mean the object stopped casting a shadow.

The fact that you can look into a beautiful golden sunset without harming your eyes is due to the shadow Earth's atmosphere casts on you. Most of our atmosphere is O2 and N2, which scatter shorter (UV, violet, blue) wavelengths via Rayleigh scattering. At noon, the Sun's light passes down through the least amount of atmosphere, encounters the least scattering, and is therefore truest to its actual color. As the Sun sets, its light must travel through ever more atmosphere to reach our eyes, losing more and more shorter wavelengths (and intensity overall) to scattering. This is why the sky is blue and the Sun becomes dimmer and redder as it sets. Smoke particles are much larger than O2 and N2, and scatter even longer wavelengths (green, yellow), leaving us with those awesome and foreboding deep red sunsets.

Here's an image of a shuttle launch shortly after sunset that demonstrates all of this, and more...

At ground level, the smoke trail is dimly lit because it's in Earth's shadow. You can see that same shadow in the dark sky just above the horizon. Had the launch occurred just east of the Rocky Mountains or mid-town Manhattan you'd see a shadow of the sunset skyline on the eastern horizon. You've probably seen the shadows of clouds opposite the sun at dawn/dusk. If you turned to face the sunset, you might see the "crepuscular rays" which are the projection of those shadows through the atmosphere. This launch occurred during a full moon, when the moon is directly opposite the sun. The shadow of the smoke trail (a crepuscular ray) can be seen terminating at the moon. You don't see that shadow emanating from the bottom of the plume because that part is already in the earth's shadow. You don't see the shadow emanating from the top of the plume both because there is less atmosphere to scatter light up there, and because the trajectory has changed to be across our angle of view, spreading what little shadow there is across a wider swath of the image.

As you climb up the smoke trail, you see the emergence of red, orange and then yellow. The sun hasn't yet set at those altitudes, and the trail is being directly illuminated through decreasing amounts of atmosphere. The higher you go, the less blue is scattered out. Ultimately, the top of the plume appears as bright and white as the midday sun. If you look out to the horizon, you see the same progression from shadow to red, orange and yellow. Yet, unlike the smoke trail, the sky does not get brighter as elevation increases. That's because the warmer hues near the horizon are the cumulative scatterings of many miles of atmosphere. As you climb higher in the sky, there is less atmosphere to scatter light of any color and the sky grows darker. That the sky overhead remains blue into darkness is due to absorption of longer wavelengths by atmospheric ozone at high altitude.

My father exposed me to the limitations of our senses, and never passed up an opportunity to carry us beyond them. Rather than follow his path into mechanical engineering, I went into electrical, almost entirely because the electromagnetic spectrum is so much more than we can sense and electricity is so much faster than machines. I wanted to use and make tools to expand my reach. I'm now in my sixth decade of that glorious road trip.

 

I'm more interested in how I'm seeing the long blue, straight, streak that intersects what I'm seeing as the sun but may be the moon.

[Madelaine McMasters]

8 hours ago, Silent Mistwalker said:

 

I'm more interested in how I'm seeing the long blue, straight, streak that intersects what I'm seeing as the sun but may be the moon.

That's the full moon, directly opposite the setting sun. If that were the exact instant of "full", the sun would be as much below the western horizon as the moon is above it. I suspect that photo was taken hours before full, so the moon is higher in the sky than the sun is below. Nevertheless, the anticrepuscular ray you're seeing is the shadow of the smoke plume on... the sky. Remember, the sky is not transparent. If it were, we couldn't see it. During a lunar eclipse, the shadow of the Earth falls exactly on the moon. In that photo, it's a near miss. As I mentioned, you can see both the shadow of the plume in the sky and the shadow of the Earth on the far horizon.

Here are some crepuscular rays (looking towards the sun)...

In the first two images, you're seeing shadows of clouds in the sky. In the last image, you're seeing the shadow of the mountain range. If you turn 180° from those views, you'd see the rays converging on the opposite horizon, forming mirror image shadows of the clouds or mountain range. I saw this happen on a childhood road trip through Wyoming, where we had the real Rockies in front of us at sunset, and the shadow Rockies in the sky behind us.
 

Edited October 20, 2021 by Madelaine McMasters

[Rolig Loon]

49 minutes ago, Madelaine McMasters said:

I got called into the department chair's office to discuss that, and the fact that the average grade I'd given was "C". I noted that the student handbook stated "C" indicated average performance.

He: We like to think that our students are above average.
Me: This is Milwaukee, not Lake Wobegon.

I taught at least one Intro course in my end of the sciences for two decades before I jumped ship and ended up in administration. That battle over "average performance" can't be won, I'm afraid.  The problem is that we can't agree on what "average" means in this context. As faculty, we seem to be comparing each student's performance to some ideal. A student who outperforms our expectations gets some kind of an A or B. One who underperforms gets a D or an F. One who just meets the expectation without distinguishing herself in either way gets a C.  We aren't comparing the students to each other but to our expectations, using the word "average" to mean "ho-hum".

Students don't see it that way. They are comparing themselves to other students, so they are using the word "average" in a more statistical sense, visualizing some sort of a bell-shaped curve for the small population in the same classroom. If the course is challenging, I've found that an unrealistically high percentage of students assume that everyone will be having a tough time but they are at least smarter than the poor slobs in the middle of the distribution.   Therefore, they expect to be getting the As and Bs for outperforming everyone else. (This is sort of like the answer to the question "How fast do you have to run to escape a bear?"  >> Just faster than the guy next to you.)   

Over time, the student version has been gradually winning the battle.  We may hold the gradebooks, but we are outnumbered. Every year brings a new team of students who are always young and persistent, and who have already been acculturated to think of themselves as "above average".  We just keep getting older and tired of fighting the same battle over and over again.  We apply an offset to our expectations so that "ho-hum" becomes a B and fewer students whine about how unfair we are.  

There are loads of complicating factors too. For example, students take many classes so they can easily compare faculty to each other; faculty members don't usually see what goes on in other classrooms. As a result, students can play faculty off against each other when it comes time for course evaluation. Pre-tenured faculty are especially vulnerable to claims that they  are "tough graders", so they lower their expectations to compensate.  

In the end, whether we like it or not, we are all living in Lake Wobegon.

[Madelaine McMasters]

2 minutes ago, Rolig Loon said:

In the end, whether we like it or not, we are all living in Lake Wobegon.

I had a marvelous professor for my freshmen year "Statics" and "Dynamics" classes. For "Statics" class, he announced that all exams would be open book, open note, open neighbor, and that he graded on a curve with the class average being "C". It took a while for the reality of that to sink in as our massive collaboration resulted in all of us getting exactly the same grade... C.

Dynamics was closed book/note/neighbor. We had grades ranging from F to A.

We don't always learn only what's on the syllabus.

[Silent Mistwalker]

17 minutes ago, Madelaine McMasters said:

That's the full moon, directly opposite the setting sun. If that were the exact instant of "full", the sun would be as much below the western horizon as the moon is above it. I suspect that photo was taken hours before full, so the moon is higher in the sky than the sun is below. Nevertheless, the anticrepuscular ray you're seeing is the shadow of the smoke plume on... the sky. Remember, the sky is not transparent. If it were, we couldn't see it. During a lunar eclipse, the shadow of the Earth falls exactly on the moon. In that photo, it's a near miss. As I mentioned, you can see both the shadow of the plume in the sky and the shadow of the Earth on the far horizon.

Here are some crepuscular rays (looking towards the sun)...

In the first two image, you're seeing shadows of clouds in the sky. In the last image, you're seeing the shadow of the mountain range. If you turn 180° from those view, you'd see those rays converging on the opposite horizon, forming mirror image shadows of the clouds or mountain range. I saw this happen on a childhood road trip through Wyoming, where we had the real Rockies in front of us at sunset, and the shadow Rockies in the sky behind us.
 

 

There. See? A straight shadow cast by a crooked column. 🤭

I was pretty sure that was the moon with the sun light being reflected by the moon in such a way as to make it look like the sun glowing. It had to be since the angle of the sun light was coming from the upper left of the image and not from the disc on the lower right.

Shadows at play. Fascinating.

Edited October 19, 2021 by Silent Mistwalker

[Madelaine McMasters]

23 minutes ago, Silent Mistwalker said:

 

There. See? A straight shadow cast by a crooked column. 🤭

I was pretty sure that was the moon with the sun light being reflected by the moon in such a way as to make it look like the sun glowing. It had to be since the angle of the sun light was coming from the upper left of the image and not from the disc on the lower right.

Shadows at play. Fascinating.

What's interesting here is that you're seeing shadows being cast through a translucent medium. Light travels in straight lines, so if you're looking "across the shadow", that's what you'll see. Even so, it's quite possible for crooked things to cast straight shadows, or shadows with vastly different shapes than you expect...

 

[Silent Mistwalker]

9 minutes ago, Madelaine McMasters said:

What's interesting here is that you're seeing shadows being cast through a translucent medium. Light travels in straight lines, so if you're looking "across the shadow", that's what you'll see. Even so, it's quite possible for crooked things to cast straight shadows, or shadows with vastly different shapes than you expect...

 

 

On Earth light travels in a straight line, yet light traveling in a straight line isn't always true.

https://www.science.org/content/article/light-bends-itself

And of course there is gravitational lensing.

https://hubblesite.org/contents/articles/gravitational-lensing#:~:text=What Is Gravitational Lensing%3F&text=A gravitational lens can occur,through a giant magnifying glass.

[Rowan Amore]

4 hours ago, Sam1 Bellisserian said:

TIL that people really do use the SL voice morphers and they actually are very good at deceiving people.

Which makes the entire statement 'voice verified' worthless.  Sure feeling sorry for all those people who won't know for sure who they're bumping pixels with.  😆😂

[Silent Mistwalker]

2 minutes ago, Rowan Amore said:

Which makes the entire statement 'voice verified' worthless.  Sure feeling sorry for all those people who won't know for sure who they're bumping pixels with.  😆😂

All the more reason to not ever. Never have to wonder about something that never happened. Maybe I'm a little bit smarter than people want to give credit for. 🤭

[Madelaine McMasters]

46 minutes ago, Silent Mistwalker said:

 

On Earth light travels in a straight line, yet light traveling in a straight line isn't always true.

https://www.science.org/content/article/light-bends-itself

And of course there is gravitational lensing.

https://hubblesite.org/contents/articles/gravitational-lensing#:~:text=What Is Gravitational Lensing%3F&text=A gravitational lens can occur,through a giant magnifying glass.

In the context of the images we're considering, the bending of spacetime is imperceptible, even to the most sensitive of man-made instruments. One might also argue that it's not the light that bends, but rather the spacetime through which it travels.

Though it would be awesome to witness the warping of spacetime with the naked eye, either we or the experience would terminate before we could appreciate it.

You first!

;-).

[Silent Mistwalker]

41 minutes ago, Madelaine McMasters said:

In the context of the images we're considering, the bending of spacetime is imperceptible, even to the most sensitive of man-made instruments. One might also argue that it's not the light that bends, but rather the spacetime through which it travels.

Though it would be awesome to witness the warping of spacetime with the naked eye, either we or the experience would terminate before we could appreciate it.

You first!

;-).

 

Let's do this!

[Lindal Kidd]

5 hours ago, Madelaine McMasters said:

In the context of the images we're considering, the bending of spacetime is imperceptible, even to the most sensitive of man-made instruments

While I completely agree with your argument, it turns out this statement isn't exactly correct. With the latest atomic clock, they've managed to measure the difference in the passage of time due to a difference in gravity, across a height difference of only one millimeter. Astonishing! This is a relativistic phenomenon predicted by Einstein's general relativity, but we normally only notice it in enormously accelerated frames of reference (such as the extension in the half lives of certain atomic particles traveling near lightspeed in particle accelerators).

https://thehackposts.com/general-relativitys-time-dilation-was-captured-across-a-millimeter/

[Madelaine McMasters]

15 minutes ago, Lindal Kidd said:

While I completely agree with your argument, it turns out this statement isn't exactly correct. With the latest atomic clock, they've managed to measure the difference in the passage of time due to a difference in gravity, across a height difference of only one millimeter. Astonishing! This is a relativistic phenomenon predicted by Einstein's general relativity, but we normally only notice it in enormously accelerated frames of reference (such as the extension in the half lives of certain atomic particles traveling near lightspeed in particle accelerators).

https://thehackposts.com/general-relativitys-time-dilation-was-captured-across-a-millimeter/

Ooooh, I stand both corrected and impressed! Thanks for that heads up, Lindal.

[BjorJlen]

   Oooo, so much good science discussion going on! I know there is no way I could ever keep up with you all, or add anything even remotely close to the discussion in a meaningful scientific way, but I just want to say keep it up! 🙂 I am so enjoying the discussion and good reads here. Maybe you could start a science/engineering class here @Madelaine McMasters, with a variety of topics for discussion and education every week. That would be awesome! 👍😁👍

   And @Silent Mistwalker, I will never look at a corncob the same way again lol (though I did hear a rumor a long time ago that this indeed was used). My, what a unique interesting species Earthlings are. 😁 Thank you for the info...

Peace...

[Prokofy Neva]

16 hours ago, Prokofy Neva said:

https://www.quantamagazine.org/first-time-crystal-built-using-googles-quantum-computer-20210730/

I tried to make these in SL but you know, somebody else should do it.

[Lindal Kidd]

Well, Prok...either you did or you didn't, until we read out the qubit!

[Rolig Loon]

As long as we are in a scientific mood, here's a bit of historical information that I forgot that I knew until I was reminded recently.  Earth's core is largely made of iron and nickel, plus about 20% of lighter elements (mostly silicon). We know this much by studying the rate at which seismic waves travel through it. Geophysicists had discovered the outer core, a molten region,  in 1906. Their studies of seismic waves indicted that Earth was molten below about 2900 km of the planet's surface.  The existence of the inner core, however, wasn't known until 1936.  That year, Danish geophysicist Inge Lehman became curious when she analyzed faint waves that seemed to speed up and be refracted by solid material. Her  published report ( entitled simply, "P" ) strongly suggested that there was a solid core deep within the molten mass and calculated its radius to within 10% of the value accepted today. Like most women in the field at the time, Lehman did not have a prestigious position but had been hired to do mathematical analysis in a rather small branch of the Copenhagen Observatory. Her work was verified a few years later by leading scientists and remains one of the major scientific discoveries in modern times.

[Madelaine McMasters]

3 hours ago, Lindal Kidd said:

Well, Prok...either you did or you didn't, until we read out the qubit!

Or she both did and she didn't?

[Madelaine McMasters]

3 hours ago, BjorJlen said:

Maybe you could start a science/engineering class here @Madelaine McMasters, with a variety of topics for discussion and education every week.

Though I appreciate the suggestion, I think the people of the forum hear quite enough from me already, BjorJlen.

[Silent Mistwalker]

2 hours ago, Rolig Loon said:

As long as we are in a scientific mood, here's a bit of historical information that I forgot that I knew until I was reminded recently.  Earth's core is largely made of iron and nickel, plus about 20% of lighter elements (mostly silicon). We know this much by studying the rate at which seismic waves travel through it. Geophysicists had discovered the outer core, a molten region,  in 1906. Their studies of seismic waves indicted that Earth was molten below about 2900 km of the planet's surface.  The existence of the inner core, however, wasn't known until 1936.  That year, Danish geophysicist Inge Lehman became curious when she analyzed faint waves that seemed to speed up and be refracted by solid material. Her  published report ( entitled simply, "P" ) strongly suggested that there was a solid core deep within the molten mass and calculated its radius to within 10% of the value accepted today. Like most women in the field at the time, Lehman did not have a prestigious position but had been hired to do mathematical analysis in a rather small branch of the Copenhagen Observatory. Her work was verified a few years later by leading scientists and remains one of the major scientific discoveries in modern times.

 

Some more to chew on. 🤭

https://www.deseret.com/u-s-world/2021/3/9/22319588/earth-core-hidden-layer

https://astronomy.com/news/2021/03/earth-has-been-hiding-a-fifth-layer-in-its-inner-core

[BjorJlen]

   I just wanted to add something I found very interesting and informative (generally speaking). Plus it has a good message at the end, so double win. Enjoy...

Peace...

[LittleMe Jewell]

Yes, the thread is a few months old, but I was fascinated by this info that I read today.

Common blanket octopus:
They are immune to jellyfish stings and will use ripped-off jellyfish tentacles to hunt for prey like small fishes.
Mating behaviour:  The third right arm in male blanket octopus is called the hectocotylus, which has a sperm-filled pouch between the arms. When the male is ready to mate, the pouch ruptures, and sperm is released into the arm. He then cuts this arm off and gives it to a female. It is likely that the male dies after mating. The female stores the arm in her mantle to be used when she is ready to fertilize her eggs. She may store several hectocotyluses from different males at once.

@Dave23McMasters - You aren't a Blanket Octopus, are you?

[Dave23McMasters]

45 minutes ago, LittleMe Jewell said:

@Dave23McMasters - You aren't a Blanket Octopus, are you?

Oh hell no!

Like mom, I wouldn't give up anything for sex, especially if it kills me. If there's a kind of octopus that snacks on noisy little humans, I'm that kind.

Here I am as a baby...

Here's Dave11 waiting for breakfast...

Here's Dave3 hunting for breakfast...

Here's Dave9 playing with our next door neighbor...

Finally, here's a little video of me catching breakfast...

Let this be a warning to the crabby people in this forum.

[LilNosferatu]

today I learned:

A couple years ago, Microsoft tried a 4-day workweek in Japan and gave everyone Fridays off. They also said meetings should be no more than 30 minutes long, and the amount of meetings in general should be reduced by using online messenger apps. Productivity jumped 40% compared to the same period the previous year.

https://www.cnn.com/2019/11/04/tech/microsoft-japan-workweek-productivity

[Madelaine McMasters]

1 hour ago, LilNosferatu said:

today I learned:

A couple years ago, Microsoft tried a 4-day workweek in Japan and gave everyone Fridays off. They also said meetings should be no more than 30 minutes long, and the amount of meetings in general should be reduced by using online messenger apps. Productivity jumped 40% compared to the same period the previous year.

https://www.cnn.com/2019/11/04/tech/microsoft-japan-workweek-productivity

I sought out co-op jobs and internships during my college summers. One of them, unpaid, was in the engineering department of a large company. My father urged me to take it.

I was placed in a week long indoctrination seminar with a bunch of new employees, where we were to be taught how to brainstorm. The opening statement by the instructor was "there are no bad ideas". My head is full of those, so I raised my hand, objected, and was told I wasn't getting into the spirit of the class. I continued pushing back and was ultimately pulled aside and asked to "cease and desist". I replied "you said there are no bad ideas!" I struck a deal in which I was given all the brainstorming problems and allowed to work on them by myself. I got a four day head start working in the engineering lab as a result. At the end of the week, I'd produced solutions that were as good or better than anything coming from the groups. I also produced a few journal articles (I was a library rat) like this...

https://homepages.se.edu/cvonbergen/files/2013/01/Productivity-Loss-In-Brainstorming_Toward-the-Solution-of-a-Riddle.pdf

Decades of research has show that brainstorming doesn't work (Google "brainstorming doesn't work" for more from the land of the obvious).

I had the advantage of being raised by an engineer who'd discovered this while doing contract work for the government. He wanted me to experience the "daft thinking of large groups" first hand. I eventually spent a dozen years working for a small company that had no use for brainstorming, and preferred to find the problem solvers in the company and then just get the hell out of their way. I thrived there until GE purchased the company, deemed me "high maintenance" and laid me off.

We all know there's an infinitude of bad ideas on the path to the plentiful good ones. It's the fear of failure that impedes our creativity. The best organizations minimize that fear by creating an environment in which failures are not punished, but rather briefly celebrated, learned from, and put to rest.

Edited January 18, 2022 by Madelaine McMasters