Whiro would not strike Earth. That was what they were calling it, after the Maori god of death. The International Astronomical Union had been slow to name it. Maybe they thought it would seem less threatening if it was just a number. Whatever their reason, they missed their chance. Some jokers on Reddit got tired of waiting and set up a poll to crowdsource a name. Deathy McDeathface had led the voting until an eleventh hour charge by a Kiwi sockpuppet brigade pushed Whiro over the top.
Anyway, that was the pronouncement from NASA and the IAU: the thing, whatever you wanted to call it, would not strike earth. After it's original maneuvers into its rendezvous orbit, the object had behaved like any mass under the influence of the sun's gravity. In time the human observers tracking it had determined that its orbit was not taking it directly toward earth, but a bit closer to the sun: its orbit would take it through the L1 Lagrange point of Earth's orbit instead.
Humanity shat itself with relief. Some people claimed that it had all been a mistake, that it wasn't an extra-terrestrial technology at all. It would pass us by, they said, and just become another near-earth object to be tracked. But the scientists observing it noted that the L1 point, the gravitational balance point on a direct line between Earth and the sun, was an ideal vantage point for Earth observation. The object could track the Earth from a "safe" distance of 1.5 million kilometers.
The cautiously optimistic suggested that it would take up station there and simply observe. For a while, it looked like they were right. The object parked itself, there between the Earth and the sun, and for two hundred and eleven days nothing happened. Then it started unfolding.
There was no announcement from any official agency on the day it started. Instead, there was an eruption of strange rumors on Twitter. Contacts at JPL say something strange happening with Whiro. Whiro activity sighted, expect IAU announcement! The tweets were redundant, echoing and echoing the same information. The only real common thread among them was repeated references to "unfolding" or "growing", but he couldn't tell at first what that might mean. One amateur astronomer further muddied the waters by saying things like events are unfolding at NASA, and new events unfolding with Whiro.
Soon the official silence became irrelevant. The truth was visible in the sky. Independent solar observers from around the world started posting pictures of the sun, a small, stark, black blot like dead pixel the center. As time went on, the blot got larger, and at high resolution, its edge showed a clearly artificial, geometric character. All the angles were exactly sixty or one hundred twenty degrees, as if it were made of packed equilateral triangles.
Measurements showed that the thing was growing geometrically, like a piece of paper being unfolded. And fast. The occluded area doubled about every three and a half hours.
He did the math. To completely block the sun from the entire earth, a disk centered at the L1 point would have to be as wide as the Earth, plus a big margin. How big? The ratio of the margin to the radius of the sun would be about the same as the ratio of the L1 distance and the solar distance.
He worked it out. The mass of Whiro was enough. Flattened out to the thickness and density of a piece of metallized mylar, it could easily shade the entire Earth. At that point it would be like a huge solar sail, and maybe, in the end, that was all it was, but since nobody knew how the thing had propelled itself to begin with, he didn't want to count on that.
The boys were at day camp and daycare. She was at work. He texted her, "It's time to go to the cabin. I'll get the big one. You get the little one. Meet me at home."
