Posted by Martin Mobberley at 10:35 on 2013 Jun 21
Nick,>I suppose because these planetarium packages are not downloading data in real time at best all they can do is plot the path rather than give minute by minute positional data.<Downloading data in real time isn’t the issue when it comes to knowing where the NEO is. The first issue is the accuracy of the orbital elements used to calculate the NEO’s position. For brand new NEOs these elements will be very rough, but with more measurements of the NEO’s position, by observers such as Peter Birtwhistle, the orbital elements become far more accurate. Planetarium packages can easily calculate the position for each minute, but when the object is close to the Earth a number of traps lie in wait. If the object is so close that Earth’s gravity starts to play a major role it is better to use the MPC ephemeris position, set for your location on Earth. Planetarium packages work perfectly well until an object is extremely close to the Earth.If geocentric coordinates are used (that is, the observer is assumed to live at the Earth’s core) the object’s position will become increasingly inaccurate as the object closes in….. When CCD fields of view can be aquarter of a degree or smaller this can lead to an object being missed.But downloading data in real time is not the issue, just having accurate orbital elements (these are often updated daily for critical objects), stating your position on Earth accurately and, for the closest NEOs, having software that can cope with an object influenced by Earth’s gravity….for very close NEOs the MPC predictions will be the best.Martin