[dard]

I actually work on NEO Surveyor telescope (surveying for dangerous asteroids), writing the simulation code use to track expected performance. So simulating +20 million asteroids and what will be visible during the mission. Motion is how we determine if there is an asteroid or just some static sky source (IE: star).

However your comment is not correct, everything moves, even in the days leading up to a potential impact things are constantly in motion. The only asteroids which appear stationary actually tend to be quite far away and just happen to be moving at just the right speed.

Things which are close to us, even impactors tend to have large angular velocities, very VERY few things come directly radially in. A part of this is that the Earth is rotating, if you are familiar with the parallax effect then the Earths rotation causes parallactic motion of the asteroids when close. IE, take a photo, wait 4 hours, and you, an observer on Earth, has now moved. The geometry has to be just right for close objects to be stationary, and a different observing position on Earth (or space) will see the object moving even if you see it stationary.

[phkahler]

Earth is about 8000mi across. The moon is about 239000mi away. Looking at it from opposite sides would be about 0.016 degrees of angular displacement. And that's a couple days from impact.

>> So simulating +20 million asteroids and what will be visible during the mission.

How many impacts do you simulate? These are the ones we care most about, and I still think they will be the hardest to detect.

[dard]

Here is a simulation I did in response to your comment, this is ~6 million impactors and their on sky velocity as they approach Earth. Dotted black line is our expected detectability limit, anything to the right of that is detectable. On sky velocity is measured in degrees / day.

https://www.dardahlen.com/6m_impactor_vel.png