Fast-moving objects near our earth have different paths in the sky. They are different with stars far away.

For telescopes, when we do not know an object's orbit, catching up with its orbit and not losing it is a problem ? How to figure out a new object's orbit parameters quickly before we lose it? For an old object with an irregular orbit, can a telescope track it?

The typical speed in the asteroid belt may be smaller than 1"/min? But there may be faster objects. Then the paths are not so simple and regular.


1 Answer 1


Specialty hardware will be able to do it, as might clever programming if you have a commercial, computerized mount and feel like hacking away. Either way, an ordinary mount will be able to follow targets in the asteroid belt easily -- their motion across our sky isn't actually very fast. What I'm about to write really only applies to NEOs.

With NEOs, the problem isn't just the apparent speed of the objects across our sky, it's that the objects are usually in irregular orbits while moving at that speed. This is in addition to the apparent motion due to the rotation of the earth.

To track these objects you'd have to project the position of the object onto our sky, using the object's ephemeris data as your starting point, then add the apparent motion due to the rotation of the earth. That position could be calculated by the mount or calculated by a computer tethered to it, which would send updated pointing directions to the mount. The specifics on how to do this depend on your hardware. It's not a small project.

  • $\begingroup$ Figure that the LX5 drives on Meade telescopes from the 80s had adjustable speeds. The dial controlling the speed had markings for solar, sidereal and lunar. But for all of those objects, the dominant motion wasn't the motion perpendicular to the ecliptic plane -- it was the rotation of the Earth. $\endgroup$ Dec 22, 2016 at 14:46
  • $\begingroup$ So, it is easy to lose a new NEO? The motion of our earth dominates, 1degree/4min. Hardwares can figure out the orbit type given several positions? $\endgroup$ Dec 22, 2016 at 14:54
  • $\begingroup$ Well, the hardware could figure it out if you reversed the process and tracked the object by hand, then fed those pointing positions to a computer. But why not let the JPL do it for you? :) ssd.jpl.nasa.gov/?ephemerides $\endgroup$ Dec 22, 2016 at 15:00
  • $\begingroup$ For new objects, how can we avoid to lose them? $\endgroup$ Dec 22, 2016 at 15:05
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    $\begingroup$ I think you might be asking a slightly different question than what I originally thought. Would you update your question so it's clearer? $\endgroup$ Dec 22, 2016 at 15:10

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