Science questions not worth a thread I: I'm a moron!

[uppi]

And the units in distance would be the ones I wanted to use (km or au), right? Or is there a fixed unit used for the distance value (eg, light years or parsecs)?

The first part is a dimensionless quantity (essentially you are taking the sine of an angle), so uou can plug in the distance with any unit you like.

 

[Cheezy the Wiz]

What determines the range of light visible to the human eye, or to any eye?

 

[Gigaz]

If a photon with the right energy hits your retina, it can trigger a chemical reaction which in turn leads to a signal that goes from the eye into your brain. I'm no expert in biology but I assume there is a bunch of possible chemical reactions for different photon energies. If the photon is too weak or too strong to trigger any of them, you won't see it.

 

[peter grimes]

What determines the range of light visible to the human eye, or to any eye?

well, ultimately selection pressure was the 'force' that resulted in the specific qualities and shortcomings of our vision.

But if you're asking on physical level, then it comes down to the way photoreceptors on the surface of our retina interact with photons:
http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.html

The active substance in the rods [not the color receptors, but similar principle] is rhodopsin. A single photon can be absorbed by a single molecule that changes shape and chemically triggers a signal that is transmitted to the optic nerve. Vitamin A aldehyde also plays an essential role as a light-absorbing pigment. A symptom of vitamin A deficiency is night blindness because of the failure of scotopic vision.

...

In their experiment they allowed human subjects to have 30 minutes to get used to the dark. They positioned a controlled light source 20 degrees to the left of the point on which the subject's eyes were fixed, so that the light would fall on the region of the retina with the highest concentration of rods. The light source was a disk that subtended an angle of 10 minutes of arc and emitted a faint flash of 1 millisecond to avoid too much spatial or temporal spreading of the light. The wavelength used was about 510 nm (green light). The subjects were asked to respond "yes" or "no" to say whether or not they thought they had seen a flash. The light was gradually reduced in intensity until the subjects could only guess the answer.

They found that about 90 photons had to enter the eye for a 60% success rate in responding. Since only about 10% of photons arriving at the eye actually reach the retina, this means that about 9 photons were actually required at the receptors. Since the photons would have been spread over about 350 rods, the experimenters were able to conclude statistically that the rods must be responding to single photons, even if the subjects were not able to see such photons when they arrived too infrequently.

 

[uppi]

In addition to the spectral responsitivities of the photoreceptors, the power of the incident light is also a factor: There is not a boundary wavelength, which determines whether you can see something or not, but it just becomes exponentially harder to see something the further away it is from the central wavelengths of the receptors.

So up to a point you can increase the power of light at a certain wavelength to make it visible. So you can see light at 800nm, if there is enough of it.

And it seems to depend on the individual too. There seem to be differences how well different people can see light at the extreme ends of the spectrum.

 

[CKS]

Physics teachers who've had cataract surgery have told me they can now see slightly shorter wavelengths than they used to be able to.

 

[emzie]

Physics teachers who've had cataract surgery have told me they can now see slightly shorter wavelengths than they used to be able to.

That sounds unlikely. Your retina is already "seeing" some UV light and infrared light. The only thing that'll allow your brain to pick up on it is a change in the retina's cones.

What's more likely is that they're able to see better than they could before, and that long enough time had passed that they were unable to compare their new vision with their vision before they developed cataracts.

 

[uppi]

That sounds unlikely. Your retina is already "seeing" some UV light and infrared light. The only thing that'll allow your brain to pick up on it is a change in the retina's cones.

What's more likely is that they're able to see better than they could before, and that long enough time had passed that they were unable to compare their new vision with their vision before they developed cataracts.

As I said, it depends on the power. So if the new artificial lens was more transmissive than the natural one for UV light, more power would arrive at the retina and the threshold for seeing light at a certain power level would move to shorter wavelengths.

If you compare after surgery to immediately before surgery, there is certainly an effect. But there also could be a difference between after surgery and a healthy eye. For that one would have to look at the kinds of material used for the natural and artificial lens and how their transmission compares in the UV.

 

[emzie]

It's just a cataract surgery, not contacts.

The mechanism you propose is no different than looking at a brighter light in the first place. Even if it were true that blue cones started firing in response to shorter wavelengths than before, your brain would still have no clue what to make of it.

 

[CKS]

In their cataract surgery, the natural lens is removed, since it is cloudy. It is replaced by an artificial lens. There is no reason to believe that the transmission in the near-UV is the same.

It seems reasonable to me that the cones in the retina could fire in response to shorter wavelengths than those that we normally see, if these shorter wavelengths are absorbed as they pass through the eye on the way to the retina. Removing the lens and replacing it with something that absorbs less in the near-UV would allow more of these photons to reach the retina and be detected.

While it is possible that my colleagues are comparing new vision with compromised vision, what they have said is that they can now see more lines in the hydrogen spectrum than they could when they were young, and that they can see more lines than their students can.

I don't see why my brain wouldn't continue to interpret blue cones firing as blue cones firing; I don't think the frequency of the light would matter to my brain.

 

[PlutonianEmpire]

It is said that recent research indicates the the sun is among the closest things in the universe to a perfect sphere. Any truth to this? If so, how? And shouldn't white dwarfs and neutron stars be even rounder? And if our sun really is this close to being uber-perfect, why not other sun-like stars?

 

[uppi]

It's just a cataract surgery, not contacts.

The mechanism you propose is no different than looking at a brighter light in the first place.

Exactly. Looking at brighter light does enhance the range of wavelengths you can see.

Even if it were true that blue cones started firing in response to shorter wavelengths than before, your brain would still have no clue what to make of it.

The brain doesn't care what kind of light made the cones fire. It just interprets blue cones firing as it always does when only blue cones fire: It generates a violet impression. It cannot assign any new color of course, but the wavelength range of violet would be extended.

It is the same mechanism that lets me see intense near infrared light as red, although it is outside of the usual visible spectrum.

 

[SS-18 ICBM]

It is said that recent research indicates the the sun is among the closest things in the universe to a perfect sphere. Any truth to this? If so, how? And shouldn't white dwarfs and neutron stars be even rounder? And if our sun really is this close to being uber-perfect, why not other sun-like stars?

I don't recall anybody saying the sun was more perfectly round than any other objects, only that it was very nearly a perfect sphere.

 

[Bluemofia]

In their cataract surgery, the natural lens is removed, since it is cloudy. It is replaced by an artificial lens. There is no reason to believe that the transmission in the near-UV is the same.

It seems reasonable to me that the cones in the retina could fire in response to shorter wavelengths than those that we normally see, if these shorter wavelengths are absorbed as they pass through the eye on the way to the retina. Removing the lens and replacing it with something that absorbs less in the near-UV would allow more of these photons to reach the retina and be detected.

While it is possible that my colleagues are comparing new vision with compromised vision, what they have said is that they can now see more lines in the hydrogen spectrum than they could when they were young, and that they can see more lines than their students can.

I don't see why my brain wouldn't continue to interpret blue cones firing as blue cones firing; I don't think the frequency of the light would matter to my brain.

In addition to this, the brain always has the capability to interpret signals for the different combinations of red/green/blue cones firing. The detectability of a particular wavelength is determined by the interaction probability of the cones, density of them, etc.
Example: If you were to give a very weak monochromatic burst of light that is carefully tuned to appear blue by calculating the absorption probabilities and densities of the three types of cones such that the red and green cones will not be triggered, you can produce an interpretation of a very weak blue color. Now if it were far outside the peaks of absorption in the near UV, and you calibrated the intensity again such that you will get a similar response as before, your brain will interpret it as the same very weak blue light of the same color even though it is of a completely different wavelength.

I have heard a story from one of my mentors when I was young, that he had a friend working at Lawrence Livermore National Laboratory with powerful green lasers. Now he was color blind to green, so appropriate accommodations were made. One day there was a slight mishap (not dangerous), and a very intense beam of green laser light accidentally shone into his eyes, and it actually managed to trigger some of his very very few green cones, so he saw the color green for the first time in his life. It was described as some kind of religious experience to him.

It is said that recent research indicates the the sun is among the closest things in the universe to a perfect sphere. Any truth to this? If so, how? And shouldn't white dwarfs and neutron stars be even rounder? And if our sun really is this close to being uber-perfect, why not other sun-like stars?

I think it sounds more like you're attempting to read the more hyperbole popular media as literal.

Now there is some truth to this, but it depends really. The sun is close to a perfect sphere because of high surface gravity. Neutron Stars and White Dwarfs are highly compact objects which in their creation process, cause the cores of stars to compact from a large radius to a smaller radius. To conserve angular momentum, they increase their rotation rate, which causes them to become more oblate along the equator which counteracts it significantly. With a rotation rate of 25 or 26 days at the equator (variable rotating because of not being solid), the sun has less of that problem. Neutron stars occasionally have "star-quakes" which is the entire star shifting to a more spherical shape due to gravity collapsing it as they slowly wind down in angular momentum due to decreasing rotation rates, and the surface tension of the crust exceeds its tensile strength. This causes the star to get a kick in its rotation now that it is more spherical, and conservation of angular momentum speeds it up again.

Now we have not measured the angular size to determine the actual size of *any* white dwarf or neutron star, so we can't say for sure how perfect of a sphere any given one is, aside from doing calculations of its mass and rotation rate to determine roughly how spherical it would be, but that depends on properties with condensed matter physics that we are less familiar with (degenerate white dwarf matter and neutron star matter are hard to work with in a lab. ). Also, we have only optically resolved the size of very few select stars, such as Betelgeuse and Altair, and the only reason is that they are huge, close, and luminous. Of these stars most of them are red giants or super giants, and their evolutionary properties cause them to pulsate, which is a very bad definition of sphericalness. Altair on the other hand, rotates very rapidly at 9 hours at the equator that it is super oblate.

I am not familiar enough with the rotation rates of other stars, but it is plausible that other stars with higher surface gravities and lower rotation rates than the sun exist to produce more sphericalness.

 

[PlutonianEmpire]

I think it sounds more like you're attempting to read the more hyperbole popular media as literal.

I figured that was most likely after seeing SS-18's response above.

Now there is some truth to this, but it depends really. The sun is close to a perfect sphere because of high surface gravity. Neutron Stars and White Dwarfs are highly compact objects which in their creation process, cause the cores of stars to compact from a large radius to a smaller radius. To conserve angular momentum, they increase their rotation rate, which causes them to become more oblate along the equator which counteracts it significantly. With a rotation rate of 25 or 26 days at the equator (variable rotating because of not being solid), the sun has less of that problem. Neutron stars occasionally have "star-quakes" which is the entire star shifting to a more spherical shape due to gravity collapsing it as they slowly wind down in angular momentum due to decreasing rotation rates, and the surface tension of the crust exceeds its tensile strength. This causes the star to get a kick in its rotation now that it is more spherical, and conservation of angular momentum speeds it up again.

Yay! You just saved me from making a post asking about exactly that at some point in the future. I now know how they get star-quakes. Learn something new every day. Thanks.

Now we have not measured the angular size to determine the actual size of *any* white dwarf or neutron star, so we can't say for sure how perfect of a sphere any given one is, aside from doing calculations of its mass and rotation rate to determine roughly how spherical it would be, but that depends on properties with condensed matter physics that we are less familiar with (degenerate white dwarf matter and neutron star matter are hard to work with in a lab. ). Also, we have only optically resolved the size of very few select stars, such as Betelgeuse and Altair, and the only reason is that they are huge, close, and luminous. Of these stars most of them are red giants or super giants, and their evolutionary properties cause them to pulsate, which is a very bad definition of sphericalness. Altair on the other hand, rotates very rapidly at 9 hours at the equator that it is super oblate.

Is that the same one that is (or might be) losing mass because of that high rotation?

I am not familiar enough with the rotation rates of other stars, but it is plausible that other stars with higher surface gravities and lower rotation rates than the sun exist to produce more sphericalness.

One thing that makes me wonder, do they take into account all those granular features/appearances on the sun's visible surface? I get the impression they up-well hundreds of kilometers with deep crevices in between them.

 

[Bluemofia]

Is that the same one that is (or might be) losing mass because of that high rotation?

Possibly. But mass loss through solar winds are rather high in massive stars to begin with due to high temperature and pressure gradients.

One thing that makes me wonder, do they take into account all those granular features/appearances on the sun's visible surface? I get the impression they up-well hundreds of kilometers with deep crevices in between them.

Surfaces are not easy to define for stars. They are usually defined as the surface of last scattering, where a photon will probably not scatter off another atom (I think 50% probability? But also depends on wavelength). It's not exactly an abrupt discontinuity from star to vacuum, sorta asking what is the diameter of Jupiter (surface defined as the distance where the atmospheric pressure is 1 ATM).

Likewise, these granulation plumes are not exactly distinct separate entities. They are upwellings of hot gas are just hot gas displacing cooler gas like a convection current. They aren't exactly liquid fountains which rise up above the surface of the sun.

Features like Coronas and Prominences are tentative features, and not included in the smoothness of them usually.

 

[PlutonianEmpire]

Ahhh, makes sense then. Thanks!

 

[emzie]

I'll be damned, I was wrong

http://www.extremetech.com/computing/118557-the-eyes-have-it-seeing-ultraviolet-exploring-color

 

[El_Machinae]

What determines the range of light visible to the human eye, or to any eye?

I've heard it said, in lecture, that our rods (the night vision ones) can transduce individual photons.

 

[Berzerker]

1) why dont the planets orbit the sun's equatorial plane?

2) why do long term comets tend to be retrograde?

3) how did Jupiter form faster than planets closer to the sun?

4) if the Earth was struck by large objects 4.5 and 4.0 bya, where did the collisions occur?