Monday, March 16, 2009

Stars of Other Worlds: HD 98618

Astronomy has always been an interest of mine, even though in my youth I was far too lazy and unmotivated to actually carry that $300 telescope outside when it could just gather dust in the basement. Among the books that shaped and informed my youth, one of the most important was Terence Dickinson's Nightwatch, a spiral-bound practical astronomy companion that contained twenty-odd pages of starcharts covering the northern celestial hemisphere. It taught me the Greek alphabet and it taught me the wonder of the stars, or at least those I could see on the fringes of a night-drowning bedroom community.

Now that I live in downtown Toronto, even when it's dark out I don't have much opportunity to stargaze. Every once in a while, I can make out a couple of constellations and a handful of bright stars, and aside from massive power outages, the rest of the sky is drowned. Still, they're old, familiar friends, and it's good to see them unchanging every time I look up. For example, consider Orion, perhaps the single most recognizable pattern of stars in the Northern Hemisphere apart from the Big Dipper.

Before the dawn of astronomy as a science, people believed the stars were fixed points in the sky and were sources of magical power. The essence of Capella could be captured in sapphires, mugwort contained the power of Regulus, and so on for all of the fifteen Behenian fixed stars. Today we know that they change over time, that five thousand years ago Thuban instead of Polaris was the North Star and that Gamma Cephei will take that mantle a thousand years from now. But the constellations themselves don't, barring supernovae, change in any time frame short of the geological.

At least, they don't change from our present perspective. Once you hop on one of those wonderful starships and head over to the verdant vistas of some other star system, they all fall into new, interesting, and inspiring patterns that may yet be filled with meaning by some other species, or by our own descendants living their lives under distant suns.

One such sun might be HD 98618. Located thirty-nine parsecs from Earth in the constellation of Ursa Major, toward the right-hand edge of the Big Dipper, it's come under some scrutiny recently because of its close correspondence to our own sun in terms of mass, luminosity, temperature, metallicity - except, apparently, a somewhat higher abundance of lithium - and the like. If you're going to be making a setting where Earth-like planets other than Earth exist, "solar twins" such as HD 98618 and 18 Scorpii are fairly natural places to put them, since we know it's already happened in those conditions once.

When you get thirty-nine parsecs away from home, the sky tends to rearrange itself. Thanks to the electronic planetarium Celestia, which no astro-fan with an internet connection should allow themselves to be without, I can travel to that distant vantage point and take a look at some old friends wearing new clothes. Here's a screenshot of a few in particular that should be familiar.

What, you don't recognize them? I didn't either, at first, but that pattern's unmistakable. Swords tend to have a purity of appearance to them. There are a handful of constellations in the sky that actually bear a passing resemblance to what they're supposed to be - Aquila, for one, as well as Crux and the Big Dipper, though that's more appropriately an asterism. Here's the same image, labeled with star names and constellation lines.

From a hypothetical inhabited planet orbiting HD 98618, it's a distinct possibility that this sword would be the single most striking constellation in the sky, as full of bright stars and mythological importance as Orion has been. There's a good reason for that beyond its shape - all of its stars, except for two, are the same ones that make up Orion.

You may recognize Betelgeuse, the bright red supergiant that gives the impression of a ruby buried in the hilt, as Orion's right shoulder. Alnitak, Alnilam, and Mintaka, which from HD 98618 form the sword's pommel and hilt, are the stars of Orion's belt. The Orion Nebula would likely figure into this constellation as well, but the version of Celestia I have does not include nebulas in its database - or if it does, I can't figure out how to display them.

It's the sort of constellation that stories about which stories would be told. Someday soon, when the stars are in the proper alignment, perhaps I will.

As for a name? That'd all depend on the background, history, and psychology of whatever sophonts are observing it. Should it be humans on that hypothetical world, though, I've been thinking something along the lines of "the Heavenly Scimitar."

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