What are the purple lights in the sky?

Decoding the Purple Lights in the Sky: What Are You Really Seeing?

Ever glanced up at the night sky and spotted a splash of purple, making you wonder if you’d stumbled into a sci-fi movie? It’s a pretty magical sight, and the good news is, there’s usually a perfectly natural explanation. These purple hues aren’t aliens (probably!), but they are a sign of some fascinating atmospheric and celestial events. So, let’s break down what might be causing those gorgeous purple lights.

Twilight’s Palette: More Than Just Red and Orange

One of the most common reasons for a purple-tinged sky, especially around sunrise or sunset? It’s all down to something called Rayleigh scattering. Basically, when sunlight hits the Earth’s atmosphere, it bumps into air molecules and tiny particles, sending the light scattering in all directions. Now, blue and violet light have shorter wavelengths, meaning they get scattered way more than red or orange light.

Think of it like this: imagine throwing a handful of ping pong balls (blue light) and a handful of tennis balls (red light) at a bumpy surface. The ping pong balls are going to bounce all over the place, right? That’s kind of what happens to blue light.

During sunrise and sunset, the sun’s light has to travel through a lot more atmosphere to reach us. All that extra distance means even more blue light gets scattered away. That leaves the longer wavelengths, including violet, to shine through. When you mix that violet with the remaining red and orange, you get those stunning purple and pink shades we all love. I remember one sunset in particular after a big thunderstorm – the sky was practically glowing purple! Weather can really amplify these colors, especially when there’s a lot of moisture in the air.

STEVE: The Aurora’s Mysterious Cousin

Then there’s STEVE, which is a mouthful: Strong Thermal Emission Velocity Enhancement. STEVE looks like a ribbon of purple and green light dancing across the night sky. It’s not actually an aurora, but it often hangs out with them. Some aurora watchers in Canada gave it that name back in 2016.

So, what is it? Well, scientists have figured out that STEVE is a narrow stream of super-hot plasma way up in the atmosphere – we’re talking 450 km high! This plasma can reach a scorching 3,000°C and zips along at 6 km/s. Crazy, right?

Unlike auroras, which are caused by charged particles raining down from space, STEVE is just glowing hot gas. It shows up as a mauve or magenta streak, while auroras tend to be green ribbons. And here’s the cool part: STEVE usually sticks around for twenty minutes to an hour. Keep an eye out for the “picket-fence” aurora too – those green vertical stripes sometimes appear with STEVE.

SAR Arcs: Earth’s Ring Current Leaking Energy

Another potential source of purplish glows? SAR arcs, or Stable Auroral Red arcs. Don’t let the name fool you; these aren’t technically auroras either. Instead, they’re a sign of heat energy leaking into the upper atmosphere from Earth’s ring current system. Think of it as a giant, donut-shaped electrical circuit circling our planet.

SAR arcs were first spotted way back in 1956. They look like a broad, faint red light that stays put even when there’s geomagnetic activity. Interestingly, recent research suggests a connection between SAR arcs and STEVE. There have even been observations of SAR arcs morphing into STEVE! It’s all still being studied, which makes it even more exciting.

Light Pillars: Ice Crystals Acting Like Mirrors

If you’re in a cold place during winter and see purple beams shooting up into the sky, you might be witnessing light pillars. This happens when light reflects off tiny ice crystals floating in the air.

These crystals are usually flat and hexagonal, and they tend to fall horizontally. Each crystal acts like a tiny mirror, reflecting the light source – whether it’s streetlights, moonlight, or sunlight. If the light source is purple, then the light pillar will be purple too. I’ve seen this a few times after an ice storm, and it’s truly an otherworldly sight.

Don’t Forget the Other Culprits

Of course, there are other things that can contribute to purple skies:

• Pollution and aerosols: Dust, pollution, and other particles in the air can scatter light and create all sorts of colors. Volcanic eruptions, for example, can release ash that tints the sky purple.
• Optical illusions: Sometimes, pink light hitting the bottom of clouds combined with a dark blue sky can trick your eyes into seeing purple.
• Urban light pollution: City lights mixing with the natural twilight glow can also create a purple hue.

The Sky’s the Limit

So, the next time you spot purple lights in the sky, you’ll have a better idea of what might be going on. Whether it’s Rayleigh scattering, STEVE, SAR arcs, light pillars, or something else entirely, it’s a reminder of just how amazing and complex our atmosphere can be. Keep looking up!