The Stack Overflow podcast is back! Listen to an interview with our new CEO.

Hot answers tagged

107

One novel solution to this: make the planet infested with a mostly harmless microbe that either inhibits the production of, or simply eats, the specific photopsins (vision pigments) found in the cone cells of the human eye. Photopsins convert light into usable energy (similar to chlorophyll), so it is plausible that a microbe might be to acquire limited ...


105

Back in the day before portable electric lights, carbide lamps were used: A mechanism dripped water onto carbide, which then gave off acetylene gas, which burned in a controlled fashion. This was used for headlights on cars and bicycles and for miners' lamps, even for lighthouse lamps. Hence, this is an obvious answer to your question. Another option is to ...


96

Give it a circumstellar cloud of oxygen. Some planetary nebulae, such as NGC 6826, appear green because of ionized oxygen. Image in the public domain. Yes, this is a true-color image. I see no reason why you couldn't surround the star with an extremely dense cloud of hydrogen, containing a relatively high fraction of oxygen, which would absorb light and ...


72

I have painstakingly assembled a highly realistic relativistic raytracing 3d renderer and plausible geometry and position for nearby stars. Here's a render of the view to starboard: I'm sure you can appreciate the thousands of hours of compute time that went into this. Less facetious answer: Leaving aside the issues of whether there's any time for your ...


65

Update I've updated my CDF to handle eccentric orbits and customization of star brightness, and (more importantly) to show long-term seasonal effects. A few notes: Mousing over any of the parameters in the upper-left will show a tooltip with its name. Note that the luminosity slider only adjusts the luminosity by a small factor. A star's luminosity is ...


49

If the glass is unflawed, the opening will look like a flat, nearly-black mirror. When you look at glass, you see a combination of the light reflecting off the surface and the light coming through it. (Think windows at night.) This is the key to Pepper's Ghost. In this case, there will be no light coming through the surface, since even glass isn't ...


46

Consider two substances with refractive indices $n_1$ and $n_2$. The reflectivity can be calculated as $$R=\left|\frac{n_1-n_2}{n_1+n_2}\right|^2$$ For air, $n\approx1$, and for water, $n\approx1.33$. Therefore, for a ray of light reflecting off of water, we have a reflectivity of $$R=\left|\frac{1-1.33}{1+1.33}\right|^2=0.02$$ The refractive index is often ...


43

LEDs From Wikipedia: Incandescent bulbs are much less efficient than other types of electric lighting; incandescent bulbs convert less than 5% of the energy they use into visible light, with standard light bulbs averaging about 2.2%. The remaining energy is converted into heat. The luminous efficacy of a typical incandescent bulb is 16 lumens per watt, ...


42

1 - Is this system viable ? It is breathtakingly inefficient. 2 - Is this scientifically possible ? Yes, the question is if you can get enough power to make it worth the trouble. 3 - How much surface should a sphere (lighthouse) have, in order to emit enough red light? It's not surface, it's power. Because you're omni-direction you'll need a lot of ...


42

No. The momentum of a photon is in direct proportion to its energy. A shorter wavelength of light has both more energy and more momentum in equal proportions. If you want to maximize imparted momentum while minimizing heating, you need to change not the light, but what it is hitting. A perfect blackbody will absorb all of the momentum of a beam of light, ...


41

When talking about telescopes there are two quantities to take into account; the “light gathering power” and the “resolving power” of the telescope. “Light gathering power” is just how much light can be collected by the telescope. “Resolving power” is a measure of the smallest angle that the telescope can reliably detect. Because light is a wave it has a ...


40

If the light coming out of the amulet is well collimated (i.e. it can form a narrow beam that does not disperse - like a laser) and the light is emitted continuously rather than in pulses, then what it does will depending on the aperture (i.e. the cross sectional area) of the amulet. Assuming a diameter of 2-3 cm (wristwatch or locket sized), an intensity ...


35

The obvious retro answer would be to use carbide lamps which work by dripping water onto a chamber of calcium carbide producing acetylene as was used on the original versions of the Model T Ford: Copyright Royce CaC2(solid) + 2H2O(liquid) -> C2H2(gas) + Ca(OH)2(aqueous) However, since the Calcium Carbide is made using an electric arc furnace, there may be ...


34

Phil Plait of the Bad Astronomy fame: Why are there no green stars: "The fault lies not in the stars (well, not entirely), but within ourselves". Followup: Green objects in space: "So, maybe, maybe, there is one intrinsically green star, but even then it’s controversial". But is there a star that’s intrinsically green? Zubeneschamali is the second ...


32

I spent some time considering how you might even start forming an ocean of blood. Mammal blood is out of question because it would coagulate. It would probably end up with rocks made of blood crust separating from watery plasma and pus. If you were sailing on an ocean of pus, any stars you'd see on the surface of the ocean would be the result of ...


32

You need to have direct sunlight that can be dispersed to see a rainbow. If you have only already dispersed light, no rainbow can occur. If you have a permanently cloudy atmosphere (like it is the case on Venus), there never will be direct sunlight, and thus no rainbows. If you need a solid physical explanation for it rather than a handwaving "different ...


31

The problem is that "focused" does not really mean "concentrated" Everyone that has ever played with a magnifying glass "know" that you can take the light from the Sun and turn it into an infinitely concentrated dot. This is in essence a variant what you are trying to do. The problem here is two things: The only reason you can get a dot that small is ...


29

Twenty-five years ago I had a friend in the military who told me about glasses he was issued that used passive technology (layers of various materials) to shift the frequency of light, allowing the user to see images at a base frequency that wasn't the original frequency (everything shifted toward the blue frequency, as I recall). For all I know he was ...


27

The problem with how a creature could evolve to use light as a weapon is inherent to the issue presented - light does not make a very good weapon. Even with all the technology that we currently have, light has several very important disadvantages: poor efficiency of generating mechanisms when approaching damage-dealing energy levels very poor energy ...


27

TL;DR: Depending on the fidelity of video you want to shoot of the aliens, you can be limited either by diffraction (low fidelity) or photon counting (high fidelity). Overall, the numbers are really large though. For example, the telescope radius for doing lip reading at a distance of 1 lightyear (~ 63000 AU) is roughly ∼92 AU (!). With a 1 AU telescope, you ...


27

On a ship traveling at exactly c, Victoria wouldn't have any time to see any stars -- for her, the ship would arrive at its destination instantaneously due to time dilation. Sorry for the slightly lame answer...


26

Sort of. Yes This would depend on how bright the light is, total radiation is surface area * brightness so to make it more visible you can increase either. It would certainly help make things easier to see, but the thing is space is really big and empty. There isn't much to run into and it's generally easy enough to avoid the things that are there (or you ...


26

TL;DR you are looking for this image: As you can see, plants depend on those frequencies for photosynthesis. They can absorb some UV light (wavelengths close to 400nm), which we naturally can't see (except for some rare people who have no lens in their eyes), but that's not optimal. Plants living in such a world would evolve different pigments for ...


26

No, it won't be realistic. The radiation pressure produced by an electromagnetic radiation of intensity, or better irradiance, $I_f$ impinging at an angle $\alpha$ on a surface can be calculated according to $P_{Inc} = \frac{I_f}{c} \cdot \left(\cos \alpha\right)^{2}$ where c is the speed of light. You immediately see that, due to the c factor, you need ...


26

In terms of what was known before, say, the 18th century, there were very limited sources of what we'd normally consider rather dim light, but fire wasn't the absolutely only light source (not counting the sun, moon -- as it was thought to give its own light in pre-Renaissance times -- and stars). Glowing insects were the commonest, and brightest. ...


25

A Programmed Feature: This idea is inspired by Willk's answer, though there have been other good ideas in the thread. It's a deliberate design choice by the long ago designers of the craft. Meant to help highlight and locate damaged components - the nanites activate a phosphorescent effect whenever chunks of the ship become separated from each other. ...


24

Sure it is possible (in theory). Moon's albedo is 12% Photovoltaic panel efficiency is around 19% (commercially available) and can go up to 40% with more exotic technologies. Assuming Moon gets the same amount of solar radiation as Earth, surface receives 1367 watts per square meter, 42% of which is visible light, which gives us 574 watts per square meter ...


23

The definition of "white" is actually rather tricky. Obviously there is no "white light" in physics. All "white" light is made up of a distribution of photons in different wavelengths. The concept of white is something in the human mind, and as famously shown, its a complicated one: Our concept of white is actually adjusted in real time based on our ...


22

Also worth touching on refractive and transparent colour - which can vary wildly depending upon specific trace elements in the glass... and which can also significantly impact reflectivity and refractive index - as can heat: some glass compositions, when unevenly heated, create surface coatings not unlike thin film, which then hugely impact refractive index -...


22

Allow me to challenge the premises: The shots that the Jedi deflect are not lasers. From the Wookiepedia:: A blaster, also called a gun, was any type of ranged weapon that fired bolts of intense plasma energy, often mistaken as lasers. The force is a great source of ***-pulls. Since the Jedi are able to see the future, if the plot requires, a Jedi might ...


Only top voted, non community-wiki answers of a minimum length are eligible