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SYFY WIRE Bad Astronomy

Magnificent Earth

By Phil Plait

On July 15, 2015, the European Space Agency launched the fourth Meteosat Second Generation (MSG-4) satellite into orbit. This advanced Earth-observing bird will monitor our planet in a number of ways, including taking very high-resolution images.

MSG-4 is in its commissioning phase, being tested out to make sure it’s fully operational. Today, the ESA released this jaw-dropping picture of the Earth taken by the satellite:

Yeah. I’d say it’s working well so far.

That picture is in color, but it’s not what your eyes would see. Our eyes have color sensitive cells in them (called cones) that are able to distinguish red, green, and blue colors; every color you see is a combination of those three. MSG-4 has 12 color sensors on board, four of which are able to detect visible light (the kind we see), and eight others that see in the infrared.

The image above is a combination of visible and infrared light. The red in the picture is actually infrared light at a wavelength of 1.6 microns (more than twice the wavelength of the reddest light you can see), green is 0.8 microns (just outside our eyes’ vision), and blue is 0.6 microns (what your eye, weirdly, would see as orange).

Sand is better at reflecting the 1.6 micron infrared light than visible, so it looks pink in the picture. Vegetation is excellent at reflecting the 0.8 micron infrared light, so it actually looks green in the image.

MSG-4 is interesting. It’s a 2.4 meter high cylinder, wider than it is tall, placed in a geosynchronous orbit. That means it orbits the Earth once a day—to someone on Earth it never seems to rise or set but stays fixed in the sky while to the satellite it always sees the same part of the Earth. That’s an obvious advantage to a weather satellite! It seems to hover over Africa and Europe, allowing long-term observations to be made.

The satellite spins 100 times per minute to stabilize itself. The Spinning Enhanced Visible and Infrared Imager (SEVIRI) takes snapshots of Earth through each of the 12 color channels, getting a picture of Earth in each channel every 15 minutes. It monitors weather as well as ozone, carbon dioxide, water vapor, and cloud, land, and ocean surface temperatures. It has a resolution of 1 km (the older sats had a resolution of 3 km).

MSG-4 will help meteorologists predict weather more accurately, and help climatologists better understand our fiercely complex environment as well. Given how GOP representatives in Congress are constantly trying to cut funding for exactly this sort of science, I’m glad to see other countries taking it more seriously.

I’m also glad to see even more beautiful images of our planet from space. They’re a reminder that our home world is swimming through the eternal blackness of space, and just how fragile, isolated, and stunningly gorgeous our precious Earth is.

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