Archive for June 21, 2012

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What point at the top of the atmosphere gets the most solar radiation on the day of the summer solstice?  Would you believe the North Pole?

Yes, that’s right. If the Earth’s pole of axial rotation were perpendicular to its orbital plane, the North Pole wouldn’t get any incoming radiation, and summer solstice would not even be defined. But with an axial tilt of only 23.5°, the pole still gets more radiation over 24 hours on the date of the summer solstice than any other point of the northern hemisphere on any date. Only the South Pole gets more, on the day of the winter solstice.

It doesn’t show up in temperature, first because much of the incoming solar radiation is scattered away during its long path through the atmosphere, and second because the ice and snow at the North Pole reflect much of the radiation back to space. (The second factor may be changing, and this is one of the reasons the Arctic is such a sensitive region.)

But suppose the axial tilt were 90°?

Uranus (Hubboe)

Uranus, as viewed by Hubble.

We do have one planet in our Solar System that approaches this: Uranus, with a tilt of 82.14°. But let’s stick with the Earth and assume it has a tilt of 90°. What would the seasons be like?

Summer solstice at the pole would be unbearable. Imagine the sun directly overhead at noon. Now stretch that noon out in time, so that the sun stays overhead for 24 hours. Hot? No place on Earth has that much incoming solar radiation today. Granted there would probably be clouds. In fact, there would probably be hurricane-like monsoonal storms unknown on our planet today. But it would still be hot.

By contrast, the South Pole would be in the middle of a six-month long night. It would have some stored heat left from the intense summer, probably enough to keep maritime climates above freezing. But it would still be dark except for the stars, the moon, and the southern lights.

The equator? At summer solstice, the equator would be pretty chilly. The sun would never rise or set, but just appear to sit at the northern horizon. As time moves toward the autumnal equinox, the sun gradually begins to rise in the north-northeast at 6 am, ride to its maximum height in the northern sky, and then set in the north-northwest at 6 pm. By the equinox, the sun would rise in the east, rise to directly overhead and then set in the west. But at the north pole, the sun has been spiraling gradually down the sky from overhead, until it finally just glides along the horizon at both poles on the day of the equinox, which begins a 6-month night for the North Pole and a 6-month day at the South Pole.

What happens if you add up all of the incoming solar energy over the course of a year? Not too surprisingly, the poles are the winners, with the equatorial regions being relatively cool. Given that water is much better at storing heat than land, the oceans would be warmer at the poles than the equator. Land areas are far more likely to follow a strong annual cycle. High-latitude continental climates would have tremendous seasonal variation, while maritime climates would be much more uniform. Monsoons, which are driven by these land-sea differences, would be extreme. And equatorial climates, which on our earth are primarily wet or dry, would be intensely cold near the solstices and as warm as they get on the equinoxes.

I haven’t actually tried this as a science fiction world—I want my planets to be habitable! But I do have a planet with zero axial tilt—Eversummer—in Tourist Trap. To quote Marna, the planet’s name must have been picked out by a publicity agent!

Note that today is the midsummer blog hop, and you can enter the draw for prizes by commenting. The prize on this blog is a PDF of one of my books, Homecoming or Tourist Trap (your choice.) In addition, anyone who comments on this blog is eligible for the grand prize drawing: 1st Prize – winner’s choice of a Kindle Touch or a Nook Touch
2nd Prize – a library of science fiction romance titles donated by various authors and an Anabanana Gift Card. Most of the books will be in digital format, with one print anthology.

No more than one comment on a single blog will count, but you can comment on multiple blogs to improve your chances.


Year 3 Day 50

African lake at sunrist, seems I am faced with a choice.

I can be treated as a god.

Or I can find some place where the People never come, and live utterly alone, perhaps for centuries.

I cannot face the second option.

I do not want to be a god. But already I have influenced these people, simply by knowing that certain things – like the fish traps or weaving clothes as they weave baskets – are possible. Can I live among them without changing them?

Some of the shamans still fear that I will diminish their authority, but most want me to stay near their gathering place. It is certainly a better place than that where my shelter is now. There is a lake, and trees, and a great abundance of wild animals. When I expressed surprise that they did not stay there, they told me that once they had done that, and the predators became too much of a problem in the lean seasons. So they wander after the herds, now, and staying in one place for more than a season is forbidden by the shamans. I am not sure they understand why.

They have made it very clear that such a prohibition would not apply to me. Am I not a god? And on a more practical point of view, I have the warnoffs, and could influence the minds of the local predators.

I could move the shelter here. After all, I rebuilt it from the escape capsule once. It would mean shutting down the computer for a while, making a new well, rebuilding the shelter—perhaps even better than what I have now.

The People would help me.

But do I really want to be a god in a temple?

Need it be that different from the summer when Songbird’s people lived nearby?

Yes, it’s a day early for the back story for my novels, but tomorrow is the summer solstice blog hop. Click the picture at the top right of the page for details, and remember I’ll be giving away a PDF copy of Homecoming or Tourist Trap, and the top allover prize is an e-reader.