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Red Cloud at Night

Week of April 10, 2000

I learned an interesting, if somewhat embarrassing lesson the other day.

My daughter is just four years old, but like her dad she loves to look at the stars and the Moon. I knew that on the evening of April 6, the crescent Moon would be close in the sky to Mars, Jupiter, and Saturn, making a pretty picture (though some people think it's an early warning of the end of the world), so I took her outside and showed her the lineup.

She thought it was very pretty, so we stayed outside for a few minutes to look at Orion, Gemini and a few other constellations. I turned back to the Moon, and noticed a red glow to the sky. The glow was very long and faint, stretching from west to east. I pointed it out to my daughter, and she saw it too. Figuring it was simply a high altitude cirrus cloud illuminated by the just-set Sun, we went back in.

I logged on to my computer to check my email, and found one from a woman who had also seen the red glow, and asked me if it were an aurora. I replied back, saying it was just a cloud, and remarked that she must live near me to have seen the same cloud!

Alarm bells should have been going off in my head. They didn't, and so it was a very big surprise just a few minutes later when I started seeing aurora alerts all over the web. Aurorae are caused when the Sun acts up a bit, sending waves of high speed particles towards the Earth. They slam into our atmosphere, causing it to glow. Spacecraft situated between the Earth and the Sun detect these particles and can send a warning to us when the Sun hiccups.

That's what happened April 6. A dramatic increase in the particle speed from the Sun indicated a massive event, and hours later a shock front of particles washed over the Earth, causing tremendous auroral displays as far south as 38 degrees (north) latitude. I live at 39 degrees. My daughter and I saw that aurora, the first I have ever seen, and I dismissed it as a cloud!

I really should have known better. First, a cloud lit by the Sun after it has set might be red, but wouldn't be red from the west horizon all the way to the east; as you look east, away from the Sun, the cloud should look darker, gray fading to black. Second, what are the odds I would get an email within minutes of my seeing this ``cloud'' from a woman who also saw it? Pretty low; if I had been thinking I would have realized something was up.

But I didn't. My expectations were that this was mundane, and so that's what I saw: a cloud.

This lesson strikes to the heart of my being a scientist. New phenomenon demand attention. A scientist-- anybody-- will try to assimilate that new event as an extension of an old one. I have seen red clouds at dusk towards the west before, so if I see something red at the same time in that direction, it's a cloud. But you have to be careful, because that kind of thinking can box you in, and you might miss something new, or something beautiful. The evidence was there for me to realize more, but I didn't appreciate it until too late (I went out later, but the aurora had faded).

The next time I see something odd like that, you can bet I'll stop and think about for a moment and not simply dismiss it. Mind you, not every unusual thing turns out to be so unusual. After all, I have actually seen red clouds hundreds of times. I expect to see a lot more, and only rarely see an aurora. So when I do see something odd, I'll have to be careful lest I fall the other way, and think every red cloud is an aurora. After all, like the saying goes: a scientist needs to keep an open mind; just not so open that their brain falls out.

If you ever see something that might be an aurora, you can learn from my mistake and check out the Solar Terrestrial Dispatch Page which has charts and images of aurorae in near real-time. Click on the ``auroral activity'' link at the top of the page.

©2008 Phil Plait. All Rights Reserved.

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