One of many cool facts brought up in Phil Plait’s new book, Under Alien Skies is that Martian sunsets are blue!

On Earth, nitrogen scatters light randomly, with bluer colors scattering more than redder colors, so the ambient sky is blue, but when you’re looking toward the sun at a shallow angle (like sunrise or sunset), most of the blue light is scattered into the next timezone and you see red and orange.

On Mars, tiny dust particles of iron oxides (rusty dust?) reflect yellow-orange light, making the daytime sky mostly a butterscotch color…but the particles that can stay aloft in the thin atmosphere are about the size of the wavelength of blue light, so they scatter blue light forward instead of randomly. So at the shallow angles of sunset and sunrise, the sky in the direction of the sun has more blue light than the yellows that are scattered in other directions.

Essentially the same process, but reversed because of the different content of the atmosphere!

Update: I’ve finished the book, and it’s well worth reading! Here’s a link to my review!

A deep orange sun against a brownish gray sky, palm fronds and power lines in the foreground.

We’ve had some ash fall over the past week, but for the most part, the air quality at ground level has only been awful, not unbearable. Especially since the heat wave subsided.

But the light has just been wrong. Normal clouds in the morning breaking up to reveal a layer of smoke behind them, letting through yellow-orange, almost but not quite late afternoon light at midday. I went out for a walk after work, once it had cooled down and saw this.

A circular halo around the sun, which is behind a tree. A contrail crosses the halo, leaving its shadow on the thin cloud layer below.

A clear 22-degree halo around the sun, bright enough that I didn’t have to adjust the image afterward. This is straight from my phone.

Even cooler: you can actually see the contrail’s shadow on the layer of cloud that’s producing the halo! The sun is behind the tree, and while the contrail pops out so it looks closer than the almost uniform layer, it’s clear from the shadow that the contrail is higher.

Smudgy clouds, colors enhanced to bring out a straight rainbow effect.

I could barely see any colors in the cloud at all without my polarized sunglasses, and when I took a photo through them, I still had to bump up the saturation.

Thin clouds and contrails cross the sky. A bright rainbow-like ring circles a spot just out of view above the frame. A fainter rainbow-like line runs across the sky below it.I’ve seen several of these over the years. The brightest one was nine years ago, while the longest was just last year. It’s a solar halo caused by reflections inside ice crystals (near ground level or higher up in the atmosphere) that in theory could circle the entire sky parallel to the horizon. In practice, it’s rare for ice crystals of the right shape and orientation to cover more than a small area from any given viewpoint, so mostly people see fragments of them.