Κυριακή, 27 Σεπτεμβρίου 2015

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Κυριακή, 20 Σεπτεμβρίου 2015

How many trees are there in the world?

Steve Jobs tells us a secret

Albert Einstein- How I See the World

Albert Einstein's Theory of Relativity

A Visit to Isaac Newton's Home

Pascals Vases - Anna Spitz Συγκοινωνούντα δοχεία

Surface of Mars - By NASA/JPL (http://photojournal.jpl.nasa.gov/catalog/PIA02405) [Public domain], via Wikimedia Commons

Can we make an artificial Earth-like atmosphere on Mars?

Short answer: Mars has an atmosphere, but it’s about 170x thinner than earth and it’s 96% carbon dioxide, making it kinda shitty for life, and we’re probably not changing this any time soon.
Long answer: Think about what an atmosphere is. It’s an razor thin envelope of gas that wraps around the surface of a planet. There’s no way to fake that. You don’t want an artificial atmosphere, so much as you are actually asking for a real bona fide atmosphere.
So what are we working with? Mars’ atmosphere is primarily CO2, so that’s a bit of a problem. Carbon dioxide is toxic to people in large amounts, so people will have to stay in doors. Additionally, air pressure is low, about half a percent of the atmospheric pressure on earth. There’s two ways increase the air pressure: add a lot of gas so the atmosphere gets a lot heavier and presses down harder at the surface level, or adding a lot of mass to the planet so that it will have a stronger force of gravity on the air, pulling down harder on the gas. I guess I forgot to mention that these aren’t really feasible. Mars’ atmosphere current has a mass of 2.5 × 1013 kilograms. This is about 1% the mass of Mt Everest. Since the mass of the planet is probably harder to change than the mass of the atmosphere, we’d need to increase the mass of this atmosphere by about 200x in order to even get close to the air pressure in the Himayalas (which is way less than sea level). Good luck getting 2 Mt Everest’s worth of gas onto Mars.
But what if we wanted to make Mars habitable? Well there’s a large science fiction literature about this idea, called terraforming. Terraforming involves processing the natural atmosphere of a planet or moon into one that is more earth like. In the case of Mars, you would want to add green house gasses to warm the planet.
Possible mechanisms include:
  1. Your first though might be to set up solar panels that will use the energy they generate to break the Martian CO2 atmosphere into carbon and oxygen. But CO2 is really stable and carbon needs something to bond with, and if this was so easy, why not do it on earth and solve global warming/climate change?
  2. Put a satellite with a mirror in orbit to focus light onto the polar ice caps, melting them. The polar ice caps are mostly dry ice, which if converted to gaseous CO2 could raise the atmospheric pressure. Unfortunately, you’ll need a really fucking big mirror to even make a dent. Annual difference due to solar weather will make more of a difference than any satellite we could currently afford to build and send to Mars.
  3. Dandridge Cole and Donald Cox suggested bringing in large amounts of ammonia from comets to serve as green house gases to melt the polar ice caps. But how do you get them there? It’s hard enough getting people to the ISS, let alone doing astronomical construction projects.
Remember, the sum of humanity has been pumping carbon dioxide into the earth’s atmosphere for the better part of 200 years, and the effects have been slow to appear, so slow that’s it’s still hard to convince Americans it matters. So now how do you get a small team of scientists to do it on a planet we haven’t even set foot on yet?
So people on Mars? Sure, might be possible in our lifetime, but they’re not going to go frolicking in the rust fields with their shoes off any time soon.

ανάλυση του φωτός

By Captain76:NikonD90+TAMRON SP10-24mm (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Why are there seven colors in the rainbow?


Short answer: There aren’t.
Long answer: Isaac Newton was one of the first people to rigorously experiment with light by observing how white light can be decomposed into a full rainbow spectrum using a prism. He observed how objects would absorb and transmit certain parts of the spectrum by separating out colors from the spectrum for experiments. By shining those colored rays on different objects he concluded that those different parts of the spectrum would not change their color if scattered. This overturned the classical theory of light, which claimed that sunlight was “pure” and was converted into different colors when scattered from objects. In short, Newton showed that white sunlight already contained those colors.

By Dispersive_Prism_Illustration_by_Spigget.jpg: Spigget derivative work: Cepheiden (Dispersive_Prism_Illustration_by_Spigget.jpg) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
You can add “Father of Optics and Color Theory” to Newton’s long list of accolades, which include inventing classical physics as well as dicking Leibniz out of his share of credit for co-inventing calculus.

Newton’s theory of color also has one more weird component, owing to Newton’s interest in alchemy and the ancient Greeks, who had a bit of an obsession with the number seven. For example they developed a correspondence between the seven known planets in the night sky and the seven days of the week (Sun-day, Moon-day, … , Saturn-day). They also only knew of seven metals, and believed each had an associated planet so the number seven is pretty ubiquitous in ancient texts.

By The original uploader was Mark22 at English Wikipedia (Transferred from en.wikipedia to Commons.) [Public domain], via Wikimedia Commons
The Seven Wonders of the Ancient World? Basically the original clickbait list.

Basically, the number seven shows up a lot in alchemy, and Newton was a bit of an alchemist. Newton originally subdivided the spectrum he observed into just five colors – red, yellow, green, blue, and violet. He revised it to include seven colors which he published in his treatise on light, “Opticks,” where he argues for a correspondence between the seven colors and the seven musical notes. This isn’t actually that weird – Newton believed the colors were cyclical (like the musical scale) so he placed red adjacent to violet, thereby inventing the color wheel. I guess when you invent as much science as Newton you’re allowed to stylize it however you want.
Anyway, to make the point one last time, take a look at this spectrum:

By Gringer (Own work) [Public domain], via Wikimedia Commons

With our modern understanding of the electromagnetic spectrum we know that visible light is any light with wavelengths between about 390 and 700 nm. This means that light comes in a continuum, with smooth transitions between colors. Furthermore, the human eye is capable of distinguishing hundreds of colors! The “Seven Colors of the Rainbow” is completely arbitrary.

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πηγή : physicsgg

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Κυριακή, 13 Σεπτεμβρίου 2015

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