Atmospheric Scattering, Friction, and Thunder: Unseen Physics Explained
TL;DR
- The sun is perceived as yellow due to atmospheric scattering of blue light, but its true color is white, observable when direct atmospheric interference is minimized.
- Atmospheric particles preferentially scatter blue light, creating the blue sky, while the remaining light, when viewed through thicker atmosphere at sunrise/sunset, appears yellow or red.
- Snow appears white because it reflects all colors of light, indicating illumination by white light, which is sunlight or moonlight, not a yellow sun.
- Photographers historically balanced color film for sunlight, which appears blue to them due to its full spectrum, requiring correction to avoid blue-tinted images.
- Friction is essential for everyday activities like walking and driving, enabling movement by providing grip against surfaces, contrary to its common perception as a negative force.
- Friction converts kinetic energy into heat during atmospheric re-entry, allowing spacecraft to decelerate without expending fuel, a process known as aerobraking.
- The sound of thunder is a shock wave from rapidly heated air by lightning, with its complex crackling sound resulting from constructive and destructive interference of shock waves from the lightning's non-linear path.
Deep Dive
The sun is not yellow, as commonly depicted, but white. The atmosphere's interaction with sunlight selectively scatters blue light, creating our blue sky and tinting the sun yellow or red when it is low on the horizon. This atmospheric effect is so pronounced that even thin clouds do not alter the sun's perceived color, which remains white when viewed directly overhead.
The scattering of blue light by atmospheric particles is a fundamental process that explains not only the color of the sky but also the appearance of the sun at different times of day. When the sun is high in the sky, its light passes through a relatively thin layer of atmosphere, and some blue light is scattered away, making the remaining light appear white. However, when the sun is low on the horizon, its light travels through a much greater thickness of atmosphere. This increased atmospheric path results in more blue light being scattered away, leaving behind the longer wavelengths of red and orange, which is why sunsets and sunrises often appear in these colors. The fact that snow appears white is evidence that it is illuminated by white light, whether from the sun or the moon, as white light is composed of all colors of the spectrum. Photographers, dealing with the full spectrum of sunlight, often have to correct for its blueness when balancing indoor and outdoor lighting, a practice that has led to counterintuitive terminology in the field where "cooler" light implies more blue and "warmer" light implies less.
Beyond the color of the sun, the podcast also explores the physics of sound in weather phenomena. Thunder, for instance, is the audible shock wave produced by the rapid heating of air by a lightning bolt. The irregular path of lightning creates multiple shock waves that can interfere with each other, accounting for the varied sounds of thunder, from sharp cracks to rumbling booms. This phenomenon is further complicated by the varying distances of different parts of the lightning bolt from the observer. The sound of hail hitting surfaces is also a consequence of atmospheric conditions; hail grows to a specific size to overcome the updrafts within cumulonimbus clouds, and the turbulence of these updrafts dictates the intensity of the impact sound. The concept of a "down pause," the silence experienced when driving under an overpass during rain, highlights how our brains often establish ambient sounds as the norm, making their absence noticeable.
Finally, the discussion emphasizes the often-overlooked importance of friction. Without friction, essential actions like walking, driving, and even resting an elbow on a table would be impossible. Friction between tires and roads enables vehicles to move, stop, and steer, while friction allows us to propel ourselves forward by pushing against the ground. The Earth's rotation itself is influenced by the collective momentum generated by human movement, though on a scale imperceptible to us due to the planet's immense mass. Even the re-entry of spacecraft into Earth's atmosphere relies on friction; the intense heat generated is a byproduct of the spacecraft's kinetic energy being converted into heat through friction with atmospheric molecules, a process that allows for deceleration without expending fuel. This highlights that friction, often perceived negatively, is a fundamental force enabling many aspects of our physical world and technological achievements.
Action Items
- Audit atmospheric scattering: Quantify blue light scattering across 5-10 different atmospheric conditions to refine sun color perception models.
- Design friction experiment: Develop a controlled test to measure the impact of reduced friction on object acceleration using 3-5 distinct surfaces.
- Analyze lightning sound propagation: Model the acoustic interference patterns of lightning shock waves based on 3-5 simulated lightning bolt paths.
- Evaluate re-entry heat shield effectiveness: Calculate the energy conversion rate of friction and shock waves during atmospheric re-entry for 2-3 simulated scenarios.
Key Quotes
"It's always yellow and this is this notion has been with us since childhood that the sun is yellow yes and that's not true it's not even close to being true uh oh and so yeah i'm sorry are there any kids watching please you might want to leave the room right now because we're not sure if there's a crayola available for you to draw your little scenes with the house and the grass and the little okay so here's the thing the sun in broad daylight is too bright to look at right without risking damaging your eyes so nobody unless of course you have perfect eyes okay so so you don't do it all right so when is the time most people ever find themselves looking directly at the sun when is that well the only times i've ever done it is sunset and sunrise sunset and sunrise exactly exactly so not only do we have the yellow crayon in our crayon box from childhood anytime we actually ever find ourselves looking at the sun either on purpose or by accident it's low on the horizon the sun is rising or setting and it has a deep yellow color sometimes it's so deep it can be red amber into red yes so and we know the sun isn't red of course it's not red we know that's an optical this isn't krypton it's not krypton exactly with their red sun so you know you know intuitively it's not red but somehow you don't know intuitively that it's also not yellow okay what color is the sun it is white"
Neil deGrasse Tyson explains that the common perception of the sun as yellow is a misconception stemming from childhood drawings and observations during sunrise and sunset. He asserts that the sun's true color in broad daylight is white, and the yellow or red hues seen at dawn and dusk are due to the Earth's atmosphere scattering blue light. This atmospheric effect alters our perception of the sun's actual color.
"So whatever the atmosphere is doing to the sun when it's high up overhead it's doing it 10 times that 10 times that and more when it goes lower on the horizon okay okay so let's see what the atmosphere is doing when the sun is overhead um in comes white light okay and uh white light is composed of colors as isaac newton demonstrated all the colors of the rainbow red orange yellow green blue indigo if you must violet violet okay so in it comes particles in earth's atmosphere that happen to be the same size as the wavelength of light of the blue side of the spectrum the blue indigo purple of violet side of the spectrum those particles preferentially scatter the blue out of the sunlight preferentially scatters it so it subtracts away a little bit just a little bit all right the rest of the light makes it all the way to earth's surface but some of the blue gets scattered and that's why we have a blue sky nice the blue sky is stolen sunlight that would have otherwise passed straight through look at that right because the sky is really clear right okay so now watch how beautiful is that though now let's have the sun get a little lower in the sky will there be more of this going on okay more of the scattering that's why on cloudless days into sunset the sun gets deeper and deeper and deeper blue the bluest sky that's why sky blue is light blue right all right you want to talk about serious right home to mama blue is the blue sky that surrounds the the twilight curtain of a sunset now you're talking blue right okay so so much blue is taken out that we now roy g biv red orange yellow green blue and took out blue indigo violet what's left red orange yellow green okay if you add those colors together you're going to get an amber sun and depending on how many particles there are you'll get a red sun or you'll get a a simple yellow sun right on the horizon and so you'll now look at the sun oh oh we have a yellow star look it's yellow no it's the atmosphere made it yellow okay it's lying to you"
Neil deGrasse Tyson explains the scientific mechanism behind the sun's apparent color changes. He details how atmospheric particles scatter blue light, creating the blue sky, and how this scattering effect intensifies as the sun gets lower on the horizon. This process removes blue light from the direct sunlight, leaving behind warmer colors like yellow and red, thus making the sun appear yellow or red to observers.
"The fact that snow looks white is evidence that it's being illuminated by white light wow that white light is either sunlight or moonlight that's right which is also a reflection of sunlight there you go this is so disturbing so disturbing sir so i'm just trying to be honest i'm just trying to put it out there and just and by the way let me take you want to go up a notch are you ready to go up a notch on this i don't know if i'm ready to go up a notch i don't think you're ready okay so um white is the sun relative to incandescent bulbs right okay your kids will have no memory of incandescent bulbs but old timers if you're over 25 you're an old timer you remember bulbs that we get hot when you put them in it was a bulb with a little piece of wire in it okay that wire used to light up oh that's a that's that sounds like a ken burns special think of the guy on the porch right i remember the days when it had a bulb with a little piece of wire in it now that wire would light up and get hot and we put a switch and we pull the switch and it gave off light now first it looked like magic okay we're gonna put you on the list for the next ken burns special the origin of the light bulb um so alright so where wasn't i i forgot what okay he's saying incandescent bulbs okay incandescent bulbs incandescent bulbs when you turn them on the temperature of the filament is not as high as the temperature of the surface of the sun and so the higher the temperature the more full that spectrum becomes so if you looked at the spectrum of a bulb in your house right an incandescent bulb it's very weak in the blue section there's some blue there which is why blue still looks blue under that light but the blue is very weak under an incandescent light bulb okay so if you bring out film that needs the full complement of blue and you take a picture under incandescent lights everything is going to be red that film if it needed the blue is called daylight film this is why there was a difference again i'm only talking to old timers here there was indoor film and outdoor film tungsten film and outdoor film and the outdoor film was color balanced to get the entire spectrum of the sunlight if you took indoor film and put it outside that indoor film is too sensitive to blue because it's making up for the feeble blue coming out of a bulb and it goes out and it's getting all the blue it ever wanted if you have indoor film took a picture outside everything looks blue because it was hypersensitive to blue and the sun has plenty of it okay so to a photographer sunlight is blue it's highly blue and they have to correct for that if they're going from indoors to outdoors
Resources
External Resources
Books
- "Experiments" by Francis Bacon - Mentioned as a collection of experiments that may not have all been conducted by the author.
People
- Isaac Newton - Mentioned as having demonstrated that white light is composed of all the colors of the rainbow.
- Aristotle - Mentioned as having incorrect physics principles, particularly regarding friction, and that his ideas were based on armchair philosophy rather than experimentation.
- Galileo - Mentioned as a bridge between Aristotle and Newton, establishing truths about nature through experiments like waxing a track to reduce friction.
Other Resources
- WD-40 - Mentioned as a product used to address squeaking caused by friction.
- Daylight film - Mentioned as film that is too sensitive to blue light when used under incandescent lights, leading to red-toned photos.
- Tungsten film - Mentioned as an alternative name for indoor film used in photography.
- Newtons laws of motion - Mentioned in relation to the principle that things in motion tend to stay in motion unless acted upon by an outside force.
- Newton's Third Law of Motion - Mentioned as the principle that for every action, there is an equal and opposite reaction, relevant to how friction connects us to the Earth.