Colors in the Skies
The Universe >
The holidays are over. It’s time to go back to school! And time for another pop quiz to test your knowledge of the cosmos! All right, no need for spitwads to the back of my head. This is just for fun, and to increase your knowledge account in the Bank of the Universe. Ready?
1. T/F Stars come in only one standard color; bright white.
Boy, you’d think so, looking at an unpolluted night sky with all the trimmings. It at least appears that all those dazzlingly sparkly things up there are white. But it’s not so.
Stars come in a wide variety of colors: red, orange, yellow, white, and blue. One question may come to mind now: Why have I, your humble purveyor of cosmic knowledge, not been institutionalized? Anyone can see clearly that there are no colored stars up there!!!
That’s actually near the truth. It appears there are no colors up there. But – sit down – most of the stars we see up there really are colored.
The fault, dear Brutus, is not in our stars, but in ourselves. Our eyes are not designed to see the blues and the red ends of the spectrum very well. The middle part of the visible spectrum, around the yellow part, we can see well, as the designers of all fast food restaurants know.
And the parts of our eyes that see color just aren’t too sensitive, either. They need a lot of energy to get them going, which is why we don’t see colors well in dark rooms.
To see the star color differences with our eyes we need to see colored stars next to each other. For example, there is a beautiful double star combo (a binary) called Albireo in Cygnus When seen through a backyard telescope one star bleeds blue, the other red.
And some stars by themselves show their true color. Aldebaran in Sagittarius shines up nice and red in the summer skies.
For truer colors one needs to use imaging equipment that is equally sensitive to all the wavelengths. That’s one reason why those images on Astronomy Picture of the Day are so colorfully stunning.
Answer: False
2. T/F The red stars are hot, and the blue stars are cold.
Most of our modern day appliances have blue colors to indicate something cold, and red to designate heat or fire. But the universe overall has its own color codes.
Stars give off energy in all wavelengths of light. But, to make a long story short, there are laws in nature that say that hot things give off a lot more of the wavelengths on the blue, high-energy end of the spectrum and not as much on the red, lower-energy end. Contrariwise cooler objects can’t spit out as much of the energetic blue wavelengths as they do the wimpier red ones. So the hotter stars actually appear bluer and the cooler stars redder.
Thus, although stars are spitting out all types of energy, what they spit out the most is what wins them their color prize.
Answer: False
3. T/F Well, then red Mars must be cooler than blue Neptune!
Planets, as opposed to stars, don’t give off their own visible light. They reflect it. And that makes all the difference in the worlds. Here’s what I mean.
Stick an iron poker in a fire for a while, and then take it out. If the fire is hot enough you’ll get the poker pretty hot, maybe even “white hot.” As it cools, it becomes yellow, then orangey, then reddish, then fades to black. The whole time that it had some color it was giving off its own light. Like stars do!
But things like planets and butterflies and hamsters named Larry and you and me don’t give off visible light. When the lights are off we are invisible.
When a light is on us, however, we reflect some of those wavelengths and absorb others. For example, a white light rains down on us all the wavelengths of light. The molecules that make up our body and clothing and everything else around are built such that they absorb some and reflect others.
If a molecule absorbs the red end of the spectrum, but reflects the blue end, it appears bluish. If it absorbs red and blues, it probably then reflects green.
It’s the same with those planets out there. They have a light source, too – our sun. Mars has compounds on its surface that reflect the redder end of the spectrum giving it that reddish-brown color.
Neptune has gases in its upper atmosphere that reflect blue light and absorb the red end of the spectrum. So Neptune appears strikingly blue.
But the colors of the planets, like the color of your clothes, have nothing to do with temperature, but with how the molecules they are made of absorb or reflect different wavelengths of light.
Answer: False.
Do better this time? Worry not if you didn’t. These are all common misunderstandings held by a lot of people, and now you are a little more knowledgeable about the universe than you were just minutes ago.
Until next time, clear skies!
Mark Ritter teaches astronomy at TVHS to students who reluctantly see these quizzes all the time. And he podcasts these articles from firstlightastro.com.
Posted by Mark Ritter at 2006.01.15 02:35 PM | Comments (0)
