COUNTERSHOCK: #scifi a medication that suppresses shock symptoms, but by itself has no pain-relieving properties.
Archive for September, 2010
MURPHY: #scifi A planet on the outer fringes of the Confederation, used as a base for exploration ships.
#scifi #climate Water is made up of two of the commonest atoms in the Universe—hydrogen and oxygen. Specifically, it is composed of two hydrogen atoms attached to an oxygen atom. For such a simple compound, it has some rather incredible properties.
It is as close to a universal solvent as any common molecule—something we do not always appreciate simply because the things dissolved by water mostly have been dissolved or (in the case of living things) have evolved membranes that keep water out. This probably played an important role in the evolution of life, and the search for extraterrestrial life is still focused on the search for liquid water.
It is both the brightest and the darkest substance on our planet—brightest in the form of snow or cloud tops (albedo 50% to 80%) and darkest in the form of deep ocean water (albedo 3% to 5%, though dark coniferous forests may be as dark.) This makes it very important in the overall albedo of Earth.
Water has a very high specific heat—which means it takes a lot of energy to change its temperature. It takes about five times as much energy to raise the temperature of a mass of water by a degree as it does to raise the temperature of the same mass of dry soil, rock or most building materials by the same amount. The result of this is that an enormous amount of energy can be stored in the oceans.
High as this specific heat is, the latent heat of water is even higher. Latent heat? This is the energy required to change phase—to evaporate water or melt ice. The melting of ice takes about 80 times the energy it takes to raise the temperature of the resulting water by 1 degree C. But this is dwarfed by the energy needed to evaporate water: 600 times the energy needed to raise the temperature by 1 degree C.
Why is this important? Because when the water condenses to form clouds, it gives that heat back to the air. But why does it condense?
Air can hold only so much water in vapor form. Further, the limiting amount is primarily controlled by temperature. Very roughly, when the temperature rises by 20 degrees F, the amount of water the air can hold doubles. When the air is at forty below (not a totally unreasonable temperature for cloud tops) it can hold about 3% as much water vapor as it can hold at freezing. At 68 degrees, it can hold about 3.8 times as much as it can at freezing. And at 80 degrees, it can hold almost 6 times as much as it can at freezing.
We’ve all seen condensation on iced drinks or cold windowpanes, when the air is holding more water vapor than would be possible at the temperature of the glass. If the air itself cools, this condensation will occur on dust particles in the air, and the result will be fog.
But when air goes up, whether it is rising because of buoyancy or because it is rising over terrain or a colder air mass, it expands and cools. The result is fog above the ground—a cloud. And as the water condenses to form a cloud, it releases the same latent energy to the air as it took to evaporate the water in the first place.
The result is a transfer of energy from the solar-heated surface or ocean to the higher parts of the atmosphere. We think of thunderstorms in terms of rain, lightning and tornadoes but they are in fact one of the most effective means of transferring energy from the Earth’s surface to the upper troposphere.
The same is true of frontal storms, but here the transfer is not only from the surface to higher in the atmosphere, but horizontal as well as vertical—from the equatorial regions to the poles.
Hurricanes deserve a post to themselves, but they also transfer energy from the ocean to high in the atmosphere. In fact, any time it rains, we are seeing a side effect of transfer of energy.
What would happen without this transfer of energy by latent heat? The winds would have to blow much harder to transfer the same amount of energy, and there would be much more contrast in temperature between poles and equator, and between the surface and the same height in the atmosphere. But the albedo and the greenhouse effect of water vapor would also change, so the overall effect on temperature would be hard to calculate and would depend very much on the albedo of the rock making up the surface of the planet.
ISOLATION SATELLITE: # scifi A satellite designed for complete biological isolation and used for study of potentially dangerous diseases. Part of the Riyan medical system.
DECENCY: #scifi Virtually all Earth cultures have a common mindset that if a part of the body is hidden, it is assumed not to exist (at least by cultural standards.). Several Confederation planets, including Central, have the mindset that hiding a part of the body for reasons other than protection or warmth calls attention to that part of the body. Thus on Central a swimming suit would be seen as indecent. (Wet suits or the modern racing suits which act to reduce a swimmer’s drag would fall under the warmth/protection/utility exception.)
INTERFACE LOUNGE: #scifi A lounge with a built-in mental computer interface. They are designed to keep the body as comfortable as possible while working with a computer, especially for long periods.
RUBY: #scifi Marna’s pet tineral. She is a bright red jewel, just old enough that her wings will no longer support her. She is descended from the four tinerals Marna initially took to the isolation satellite.
XENOTELEPATHY: Telepathic communication with a member of a non-human intelligent species.
FLIGHT: A black gelding, Thoroughbred type, being trained by Vara. He was abused by a former owner, and has a lasting fear of automatic walkers.
#scifi If we want a planet on which human beings can live, we’d better have a suitable temperature—not only one at which human beings are comfortable, but one at which water can exist in all three phases, allowing for temperature variations from equator to pole and through the height of the atmosphere. So what determines the temperature of a planet?
The starting point is what is called the equilibrium temperature of a planet. This is based on the idea that the planet is receiving energy from the sun at the same rate it is radiating it out to space.
Any object that is not at absolute zero temperature radiates energy, and at what we consider comfortable temperatures, most of that energy is in what we call the thermal infrared portion of the spectrum. We can’t see it, but we can feel it. On a very cold day, we may say that the ground and sky are radiating cold, but that is only because our skin is at a higher temperature and is radiating energy away faster than it is receiving it back.
In fact, the amount of energy an object radiates is directly proportional to the fourth power of the absolute temperature. For a planet, then, the total energy radiated is proportional to the surface area of the planet times the absolute temperature multiplied by itself four times.
But the energy received from the sun is proportional to the luminosity of the planet’s sun divided by the square of the planet’s distance from the sun times the cross sectional area of the planet. For spherical planets, the cross sectional area is one fourth of the surface area. A fraction of that radiation will be reflected out to space and can be ignored. This fraction is called the albedo, or reflectivity of the planet.
When all of these things are put together, we can get an equation for what is called the equilibrium temperature of the planet. The table shows this temperature (in degrees Farenheit) for three planets of the solar system: Venus, Earth, and Mars. It also shows their real surface temperatures.
What happened? These planets have atmospheres! The equilibrium temperature is the average temperature of the radiating layer, which is generally somewhere above the surface, in the colder part of the atmosphere. How high depends on the wavelength. In visible wavelengths, the outgoing radiation is from the visible surface—partly cloud tops (usually colder than the ground) and partly ground or ocean. Far more important is the fact that some of the gasses in our atmosphere—notably carbon dioxide, water vapor, and methane–are opaque in large parts of the thermal infrared. Most of the energy at temperatures we are comfortable at is radiated in the thermal infrared.
This is what is meant by the greenhouse effect, which actually has very little to do with why a greenhouse stays warm, especially during the day. The difference between the Earth’s equilibrium temperature and the actual temperature is a measure of the greenhouse effect with the current amounts of carbon dioxide, water vapor, methane and a few other radiatively active gasses in the atmosphere.
We are adding carbon dioxide to the atmosphere at an unprecedented rate. Further, the warming of the oceans is adding water vapor, a second important greenhouse gas, and agriculture, permafrost thawing and possibly the thawing of methane clathrates is adding methane as well. All of this means that the radiation the Earth is returning to space is coming from higher and higher in the atmosphere, and since the rate at which the air cools with elevation is unlikely to undergo major change, the surface gets hotter.
What does all this have to do with planet building? It suggests that the solar constant, proportional the luminosity of the star around which the fictional planet is circling divided by the square of the distance between the planet and its sun, had better be about the same as ours if the atmosphere and albedo are similar. If we make this assumption, we can say some things about the way the sun will look and the length of the year.
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