physique question #4526



Gordon (Genre: mâle, Àge: 16 années) de Oakville, Ontario sur 25 janvier, 2009 demande:

Q:

I was studying for a science exam and stumbled across a chapter that covered energy. The chapter states that for a flame it can have different colors for different energy levels. So I wanted to ask if blue is the highest level, then why is it that the sun is yellow when we look at it? And when you see pictures of the sun it's sometimes red, but red is the lowest and yellow is the second lowest, but everyone says that the sun is the hottest thing in the galaxy, clearly, and they also say that its energy is so vast. I dont quite understand.

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la réponse

Barry Shell répondu le 26 janvier, 2009, R:

The sun is not the hottest thing in the galaxy. There are many much hotter things out there, stars and other objects that are thousands or millions of times hotter. It's true that when it comes to colours, blue light does indeed have a higher level of energy than yellow or red. The way the spectrum works, the shorter the wavelength, the higher the energy. Blue/Violet is the shortest wavelength we can see. After that comes ultra-violet, then X-rays, and finally gama rays, each with higher energy. Wikipedia entry on the electromagnetic spectrum Our sun is not a blue star. It is a yellow star. So it's not the hottest, highest energy star in the galaxy. It's just an ordinary medium power yellow star. There are MUCH more powerful stars in our galaxy. Our sun is pretty small and ordinary, compared to some others.

The reason the sun appears red sometimes is because of the way the air in the atmosphere reflects and refracts away the yellow light (and the blue light) coming from the sun so that all you see is the red. This is not the real colour of the sun. It's just a result of optical effect of the atmosphere on sunlight.

The sun's energy *IS* truly vast compared to us, or compared to all the oil on Earth, but compared to billions of other stars and other things out there in our galaxy and especially in other bigger galaxies, our sun is rather modest and small. To see a comparison of just how small our sun is, look at this comparison chart of planets and stars.

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