3 ms·

Exactly, calculating trajectories (accurately) is very difficult. I did a summer project at JPL where we would take astrometric measurements of various minor p

by splat 13y ago

Exactly, calculating trajectories (accurately) is very difficult. I did a summer project at JPL where we would take astrometric measurements of various minor planets (including Pluto) and then update the trajectories. Even a big, well studied object like Pluto could easily be an arcsecond or two away from where it was "supposed" to be. (For reference, at Pluto's distance, that would be ~30,000 km off.) But it's also possible that it's right where it should be and is too faint to be detected. Asteroids are very hard to detect because they're faint and they move -- so you can't expose the image for a long time to detect a fainter image. All you would get would be a faint streak across the image.

ZoF 13y ago
Not if you moved the lens in time with the supposed trajectory.
- splat 13y ago
  Yes, tracking is one technique to get around this. It's generally difficult (though not impossible!) for a few reasons. The first is that most telescopes are set up to track the sky -- they can move pretty uniformly along with the rotation of the earth, but they're much jerkier when moving to other locations on the sky. In an alt-az telescope this doesn't matter, but most telescopes aren't built on alt-az mounts. The other reason this is difficult to do is because it's hard to guide the telescope. The bright guide stars you're using to correct for the small motions the telescope is making due to wind, etc. are now moving in your field of view and can't be used to guide the telescope. Finally, you have to know the trajectory pretty well to do this. You have to not only know how fast to move the telescope, but the right direction to move the telescope. This can be done for a well studied object where the uncertainty in the trajectory is pretty small. But if the object hasn't been observed for 14 years, you probably won't have very good knowledge of its trajectory.

by splat 13y ago

ZoF 13y ago

Not if you moved the lens in time with the supposed trajectory.

splat 13y ago
Yes, tracking is one technique to get around this. It's generally difficult (though not impossible!) for a few reasons. The first is that most telescopes are set up to track the sky -- they can move pretty uniformly along with the rotation of the earth, but they're much jerkier when moving to other locations on the sky. In an alt-az telescope this doesn't matter, but most telescopes aren't built on alt-az mounts. The other reason this is difficult to do is because it's hard to guide the telescope. The bright guide stars you're using to correct for the small motions the telescope is making due to wind, etc. are now moving in your field of view and can't be used to guide the telescope. Finally, you have to know the trajectory pretty well to do this. You have to not only know how fast to move the telescope, but the right direction to move the telescope. This can be done for a well studied object where the uncertainty in the trajectory is pretty small. But if the object hasn't been observed for 14 years, you probably won't have very good knowledge of its trajectory.