[ithkuil]

that's right.

another metric that affects the ... impact ... of such an event is also the speed of the asteroid. Unlike size, I suspect higher speeds would make it harder to spot (and once spotted there would be less time to take action)

[BurningFrog]

Asteroids are just as visible at any speed.

Though warning times will be shorter the higher the relative speed is.

[bumby]

I think the OPs point was:

If we are only surveying a portion of the sky at a time and a faster asteroid spends less time traversing that portion, the likelihood of detection is lower.

[AnimalMuppet]

Faster asteroids leave longer streaks.

[krisoft]

I'm not sure if you are joking.

Assuming you are not. What kind of "streak" you are thinking about? Are you thinking about comets with their tails? Or motion blur?

Because if motion blur I would expect an asteroid on a collision course to have none. (at least in the short timeframe before the collision) Because "Constant bearing, decreasing range" is how a collision looks like from a first person perspective.

[AnimalMuppet]

Your last paragraph is correct, but only very close to the collision. Things in orbit around the sun don't move in straight lines, even if their paths are going to intersect. The earlier you see it, the less it's moving straight at you.

(Of course, if it's going to hit you, the faster it's going, the more straight at you its path is at the same distance. But for the same amount of "not straight at you", faster leaves a bigger streak.)

[ithkuil]

Yeah given that were talking about objects that are colliding with the earth, the faster they will come closer to us the less time we'll have to spot them