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Jan 29, 2013

Why is the sky blue and how do we see colors?

If you stand anywhere on Earth during the day, you see the sky and it's blue. But why is it just blue and could it have had a different color?

If we had no atmosphere, the sky would be black. The atmosphere, or the air that we usually call it, consists of very small particles called molecules. The air consists of a mixture of nitrogen and oxygen molecules. To get an idea of ​​how large a molecule is, imagine a sand grain of 1 mm. You are guessing around 1-2 m long. Imagine that we enlarge you and an oxygen or nitrogen molecule so that it is as big as the sand grain. Then you get so long that your head is in Sweden while your feet are in South Africa. Let us settle for saying that they are extremely small and when the light from the sun moves near a molecule, the light can change direction.


The light from the sun consists of white light. When it rains and the sun shines at the same time, one can often see a rainbow. Then you see that the white light consists of light with different wavelengths. We see it as different colors. Look at the picture below. Lights to the left (violet and blue) have shorter wavelengths and are easier for the molecules to spread in different directions. Light to the right (orange and red) is more difficult for the molecules to spread in different directions. Rayleigh scattering as this is called light or other electromagnetic radiation scattering in solid, liquid or gaseous matter. Rayleigh scattering occurs when photons are scattered against bound electrons.


Because blue and violet sound are most widely spread, it is more likely that a photo of these colors will hit your eye than a red light photo.


For a thorough review I recommend the film "Why is the sky blue? Thoroughly Explained Here!"


Though there is a problem. If now violet has even shorter wavelength than blue light. Why isn't heaven violet?
From xkcg
It depends on how our eyes perceive colors.

Our eyes have two types of photosensitive cells: pins and rods. Rods can only perceive how bright it is, but no colors. The pins are available in three types that are sensitive to three different wavelengths.

The eye has three types of pins. They are called S, M and L cells


Because of our eyes, we perceive the violet / blue sky as blue / white instead. Our eyes cannot see the difference between blue / white and blue / violet, just as we cannot see the difference between "pure" yellow light and a mixture between green / red.

On the Youtube channel MinutePhysics, they explain why this is not heaven violet.




Please see the film below where you explain how we see colors and why it is enough with three types of pixels (red, green blue) on the screens to see all the colors.


Sources
http://spaceplace.nasa.gov/blue-sky/
http://en.wikipedia.org/wiki/Rayleigh_scattering
http://science.howstuffworks.com/nature/climate-weather/atmospheric/sky.htm
http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html
http://www.patarnott.com/atms749/pdf/blueSkyHumanResponse.pdf
http://www.youtube.com/watch?NR=1&v=Asyzw3gMfb0&feature=endscreen
http://www.msnbc.msn.com/id/8631798/ns/technology_and_science-science/t/why-skies-are-blue-instead-purple/#.UO3buonm4Vw

Jan 26, 2013

Apptips till Android: Smart AudioBook Player

För att hinna med att läsa böcker har många börjat lyssna på ljudböcker istället. Nu när de flesta har smarta telefoner så kan man ha ljudböckerna med sig alltid. Jag märkte att de ljudspelare som kommer med mobilen är värdelösa på att hantera ljudböcker. Personligen brukar jag hoppa mellan olika böcker och du kommer ljudspelaren så klart inte ihåg var man slutade. Med Smart AudioBook Player slipper du detta.


Andra smarta funktioner är
  • Automatisk pausning om man somnar när man lyssnar
  • Uppspelningshistorik
  • Ljudboks informationen uppdateras om du tar bort/lägger till filer i samma katalog.
  • Stöd för *.mp3, *.m4a, *. m4b, *.awb, *.ogg, *.wma-filer.
  • Ingen reklam
  • Kontroll för uppspelningshastighet.
  • Möjlighet att klassificera böcker (ny, oläst, läs).
  • Möjlighet att lägga till romanfigurer i en lista för att lättare kunna följa historien.
Skaparen av appen: Alex Kravchenko går själv igenom de vanligaste funktionerna nedan.
Fullversionen kostar 2 dollar

Jan 25, 2013

Mortalitetsstatistik från 1500-talets London

Om du trodde att matematisk statistik om hur människor har dött i 1500-talets London var tråkig, se denna film


En liten ordlista och länklista på några saker som nämns

bills of mortallity: Mortalitetsstatistik
St. Giles Cripplegate
belfry
All-Hallows-the-Great
lethargy
plague
bookies

Rising of the lights: Lung problems. 'Lights' is an old word for lungs. Into the twentieth century you could purchase 'cat's lights', that is to say bovine lungs as a food for cats. The phrase 'I'll knock yer lights out' refers to the lungs.

Pink Floyd: "Pink Floyd were an English rock band that achieved worldwide success with their progressive and psychedelic rock music. Their work is marked by the use of philosophical lyrics, sonic experimentation, innovative album art, and elaborate live shows."

Scowring

Fler exempel på "bills of mortality"

Jan 24, 2013

Vetenskapens hjältar som actionfigurer

Actionfigurer kommer alltid som ett brev på posten efter en barn/ungdomsrulle lämnar drömfabriken i Hollywood. Det finns en hel del Einstein dockor men nu har användaren datazoid på deviantart varit väldigt flitig med photoshop och producerat en imponerande samling vetenskapspersoner. 

Heroes of Science
Ta gärna lite tid på wikipedia och lär dig mer om dessa personer. Här finns en uppdaterad version. Bara att printa ut och sätta upp hemma eller i klassrummet.


Jan 23, 2013

Kalle Anka lär sig matematik


På julafton tittar en stor del av befolkningen på Kalle Anka. 1959 gjordes denna film om matematik med Kalle Anka i huvudrollen.
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