January 25 – Cool Customer

Factismal: IRAS was launched in 1983.

Astronomy entered a new age in 1983, with the launch of the Infrared Astronomy Satellite, or IRAS for short. IRAS wasn’t the first telescope into space, nor was it the first infrared telescope. But it was the first infrared telescope in space. And that is what matters, because it turns out that space is the place to be if you want to see something that is invisible.

The InfraRed Astronomical Satellite (IRAS) discovered the first exoplanet (Image courtesy NASA)

The InfraRed Astronomical Satellite (IRAS) discovered the first exoplanet (Image courtesy NASA)

You see, the part of the spectrum that we see is just a very, very limited part of a much wider whole. The visible spectrum, which covers the colors from blue through red, says a lot about the world. But the invisible spectrum, which covers colors that are cooler than red (the infrared) and hotter than blue (the ultraviolet), tells us a lot more about the universe. Part of that is simply because most of the universe is very, very cool. And the rest is because the parts that aren’t cool can be very hot indeed.

The hotter something is, the "blue-er" its color is

The hotter something is, the “blue-er” its color is

And it turns out that the temperature is the key to the color. Back in 1900, Planck was able to show that the color of an object was intrinsically related to its color. For example, the Sun is yellow because the part of it that we see is about 5000 K (about 8540 F, or “really, really hot”). We now use that principle in a number of ways, from taking the temperature of a star to taking the temperature of a baby.

But not all colors of light make it through to the ground. To understand this, think of a brick wall. You cannot see through a brick wall because the bricks block the visible light while allowing more energetic gamma rays to pass through. Similarly, our atmosphere blocks a substantial part of the infrared light while letting the more energetic visible light through. And, just as you can see what’s on the other side of a brick wall by walking around it, telescopes can see the infrared colors blocked out by our atmosphere by going above it.

And when they did, what an amazing array of interesting things they saw. While looking at over 500,000 light sources, IRAS discovered the source of the Geminid meteor shower. IRAS discovered six new comets. IRAS saw the dust created by asteroid collisions as a giant cloud surrounding the Solar System. And IRAS saw 75,000 different galaxies with huge numbers of new stars being born. Most importantly, IRAS gave us the first picture of planets forming from a cosmic cloud of dust and gas.

And the hits from IRAS keep coming, even though the satellite quit working nearly thirty years ago. That’s because there are lots and lots of images from IRAS and other space telescopes that need people to look through them. People just like you! If you’d like to try your hand at classifying infrared images, then try the Milk Way Project:

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