Why is red light warmer than blue light even though it is less energetic?
First, let's compare the two. Red light has a longer wavelength than blue light; this means, blue light has a higher frequency than red light. Since there is more energy in higher frequencies, theoretically, blue light is warmer than red light.However, when light passes through a prism, (as in Herschel's experiment) it is refracted in such a way that the "blue" wavelength is more spread than "red" wavelength as seen in the image below. That is the reason why the overall energy reaching the thermometer is greater in the infrared and red part than on the blue part of the spectrum.Image courtesy of: Behind the Lines: Herschel's Discovery of Infra-RedBut there is another way of looking at this. Light rays are composed of photons whose energy specifies a color from red to violet. The intensity or brightness of the light is defined by the flux, or number of photons passing through a given area in a given time. The photon flux of high energy photons needed to give a certain radiant power density will be lower than the photon flux of low energy photons required to give the same radiant power density.Animation courtesy of: Photon Flux | PVEducationIn the animation, the radiant power density incident on the surface is the same for both the blue and red light, but fewer blue photons are needed since each one has more energy. Therefore, it seems to me, a blue light and a red light of the same brightness will have the same heating effect.
Dark matter real or not?
With dark matter, what we have, essentially, is a model of gravity (you can use either Newtonian, or Einstein's GR, take your pick) that works out great, until we get to the motions of galaxies and galaxy clusters. At that point, we have motion that is too fast for these objects to stay together, and be gravitationally linked. But they do stay together.. Many scientists hypothesize that there is "missing matter" and therefore greater gravity in these situations. This Dark Matter does not interact with regular matter, or even the EM spectrum, *other* than the fact that it's gravitational interaction with "regular" matter can be detected and calculated. I personally believe, that there's just some unknown, mysterious physics going on, that we have not yet discovered. You don't have to go back too far in the history of human existence, to know that "seeing" the effects of something with mass doesn't always mean that mass is there. In the late 1800's and early 1900's, astronomers noticed the precession of Mercury's perihelion didn't behave as it should, via Newtons Laws. Many hypothesized a planet closer to the sun than Mercury, named "Vulcan" (this was well before the Star Trek series ever existed) and the mass of that unseen planet was causing the fluctuations in Mercury's orbit. Eventually, Albert Einstein came along, and, with his Theory of General Relativity, provided the mathematics to prove that "Vulcan" does not need to exist, to explain Mercury's behavior. Perhaps someone in the future, will observe a new physics, that can explain the motions of galaxies better than Dark Matter. Although this is all speculation on my part. There are other examples of gravity where either our models aren't quite right, or we are missing something, for example, the fly-by anomalies, and the Pioneer anomalies. Certainly, IMO, our knowledge of gravity is far from complete.
Are temperature ratings on all sleeping bags calculated in the same manner?
I was looking at Gander Mountain's "Guide" series -40F sleeping bag. It had a note stating: "Temperature rating applies when used in an enclosed environment when used on top of a self-inflating pad". (That's the wording as best as I can remember it. I think they were talking about one of the closed cell pads). Is it common practice for temperature ratings to apply only if you're sleeping on top of an insulating pad? Those pads provide quite a lot of insulation, don't they? The -40F bag at Gander Mountain was $130. The ones I was looking at from Cabella's website cost about twice that. http://www.cabelas.com/cabelas/en/templa... Is one -40F bag just as warm as another?
Why is Uranus colder than Neptune?
The "surface" (the surface on a Gas Giant is where the atmospheric pressure is 1 bar) temperature of Uranus is -212.2°C while the surface temperature on Neptune is -206.6°C. Keep in mind that all temperatures provided are averages...temperatures will be much colder at night on these planets than they will be at day (except Venus). This question puzzles many, as Neptune is more than 1/3 farther away from the Sun than Uranus. However, the answer is not so elusive.The answer to this question has to do with the atmospheric composition of both planets. Much like Venus and Mercury: despite being further away from the Sun, Venus is a warmer planet (179°C on Mercury vs. 460°C for Venus). The Uranian atmosphere is ~85% hydrogen and ~15% helium. The Neptunian atmosphere, on the other hand is ~80% hydrogen, ~19% helium, and ~1.9% methane. So why is Neptune warmer? The answer lies in the smallest percentage: 1.9% methane. Methane is one of the most potent greenhouse gases, and is a cause for worry on Earth. Methane serves to trap the heat entering Neptune's atmosphere, and keep it there. The composition of both atmospheres are nearly identical, but since hydrogen and helium have no greenhouse properties (on their own), the heat trapped in Neptune's atmosphere by the methane keeps it just a little warmer than Uranus.(This is the Greenhouse Effect on Earth, but this is generally what is occurring on Neptune as well).In the end, despite being 1,494,000,000 (1.494 billion) kilometers further away from the Sun, Neptune still maintains a ~6°C warmer atmosphere, due to the very high concentration of methane (1.9% on Neptune vs. 0.00017% on Earth) which serves to trap heat from the Sun.
Why are no planets found within 0.3 AU of the Sun?
They'd burn up or something. The intense heat from the sun causes it.
What would happen to my body if I stepped out onto Pluto’s surface without a space suit?
Pretty much the same thing that would happen to you if you stepped out of the ISS into the shade without a space suit. Being in a vacuum means that there’s no residual heat, so being shaded from the sun is the same as being too far away from the sun. For example, the dark side of Mercury (which is quite close to the sun) is nearly as cold as being on the dark side of the moon (you’ll get a little residual heat from the planet as the surface releases its heat back out into space if it’s a spot that’s recently been in the sun) - but step into the light when you’re that close and you’ll instantly get quite hot, about 800º F. On Earth’s moon it’s about 260º F (127º C) in the sun and about -280º F (-173º C) in the shade.Part of the reason for the massive variations is that there really isn’t an upper limit to temperatures while the coldest you can get is 0 Kelvin. That’s the point where all molecules stop moving (I don’t actually know what effect that has on sub-atomic particles). Because there’s no atmosphere in a vacuum to hold that residual heat, temperature is entirely controlled by whether the sun is shining on that spot or not. You wouldn’t freeze immediately though as it would take your body a significant amount of time to bleed off all that heat into space.Just don’t try to hold your breath and as long as you’re pulled back inside within about 30 seconds you should recover just fine. Probably could even survive a bit longer than 60 seconds, though you would lose consciousness around 10–13 seconds (maybe a bit sooner). If you were naked in the vacuum in the sun (at the ISS), you’d also likely have a pretty gnarly sunburn because there’s no atmosphere to filter out the harmful radiation. Not such a problem at Pluto though. Being in the sun on Pluto it will only be about 55 Kelvin, which is pretty flipping chilly. Bring a coat if you insist on attempting this for yourself.