Showing posts with label space. Show all posts
Showing posts with label space. Show all posts

Wednesday, February 1, 2012

Green Stars

Go to any planetarium show and they will probably point out how some of the stars are different colors. Betelguese (Orion's shoulder) is a deep red, while Rigel (his knee) is blueish white. That's because the stars are glowing bodies that emit a distribution of radiation that more or less follows the black body curve. Cool objects like candles glow red, brighter ones like incandescent bulbs are orange-yellow, and really hot things like a welder's torch or lightning are blue-white. In fact, the colors themselves are described by the temperature (in Kelvins) of an object that would emit light of that shade. You can see in the color below the path of the black body curve.
But back to the original question? Why does it skip green?

Hotter objects emit more energy than cooler ones, and the peak frequency also increases, according to Planck's Law. So logically, at some point, the peak emission wavelength should pass through green. But as this excellent (allegedly kid-oriented) video describes, when that happens, we don't see green because of how our eyes see color.

Our eyes have three cones that detect three frequencies of light that our brain interprets as color vision. When the black bodies emit at a temperature that peaks in green, it's also sending out less (but still lots of) light at nearby frequencies (blue and red). So with all that light coming in, our brain sees the green-peaking stars as white.

Tuesday, December 1, 2009

Zero-G Water Experiments

Aboard the International Space Station, you can do some crazy things with water droplets.

Monday, July 27, 2009

Goodbye Snow

No, I'm not talking about Global Warming here. This year we're saying goodbye to a different type of "snow." Also just called static, TV snow is a signal picked up by analog televisions when there is no stronger signal around. And where does this weak signal come from? Much further away than you might expect. As Scientific American writes,
The impending digital-TV transition has a forgotten victim: the big bang. You can tune an analog set between broadcast channels and see static, part of which is energy left over from the hot primordial universe. This static is known as the cosmic microwave background radiation, and its discovery in the 1960s proved the big bang theory. But on a digital TV, the best you can do is "The Big Bang Theory".
Since the the digital TV signals don't pick up this analog ambiance, the only relic of Big Bang snow on TV may be the opening sequence for HBO.