Asteroid visible during the day? In a story I'm working on, a huge, 20 by 14 kilometer, Ni-Fe asteroid attains a 1760 km. orbit around earth (why/how? Long story). I figure it has an H magnitude of ~12. Would this body be visible naked-eye from the surface during the day?
The key to answering your question is to know the albedo of the asteroid compared to the Moon. The Moon is rather dark (reflecting 7% to 12% of the light if I remember correctly, about as black as worn asphalt). I think, but do not know with certainty, that the asteroid would not be much darker.

For the dimensions that you give, the asteroid would be approximately the same apparent size as the moon: 0.45 x 0.65° compared to the Moon's 0.5°.

So both have approximately the same albedo and approximately the same size. Therefore I say that the asteroid would be visible in the daylight.

Also this is a sci-fi story, correct? If you can get the asteroid into that orbit, then anything is possible. :-)