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    Re: Cel nav in space
    From: Frank Reed CT
    Date: 2005 Jan 5, 17:52 EST
    Chas wrote:
    "Two Voyager space probes launched during the 70's are still on the JPL
    active mission list and NASA schedules regular communications sessions with
    them.  They currently are well past the orbit of Pluto and may be considered
    to be in intersteller space."
    The two Pioneers are out there, also, but JPL no longer attempts to contact them.
    "I have been considering asking the space navigators at NASA if they have
    noticed any anomolities in their trajectories as the gravitational influence
    of the sun deminishes. According to Einstein, space can actually be shaped
    by gravity fields."
    There are observed tiny anomalies in the trajectories of the Pioneer probes. Here's a link to an article: http://www.space.com/scienceastronomy/mystery_monday_041018.html
    "Maybe we might have enough knowledge navigate about our Milky Way galaxy
    but heading out to explore another galaxy who be a greatest venture into the
    unknown since Columbus sailed over the 'edge of the earth'."
    Ya know, it's a funny thing really, but we can map *other* galaxies much more easily than we can map our own. The large-scale structure of the nearest galaxies are known in considerable detail and there is no limit in principle to extending those maps. But the overall structure of own galaxy is still largely unknown. For example, there was solid evidence of black holes at the centers of other galaxies years before evidence was available of a large black hole at the center of the Milky Way (there is now solid evidence of that, too). It's so difficult to map the Milky Way because we're in the middle of all the dust. When we look at the night sky and the visible Milky Way, we're seeing only a few percent of the whole thing. With most other galaxies, we can see just about everything.
    "We would need to travel there at light speed, if that's possible. Would
    sightings need to be corrected for relativistic effects? "
    We do already! Aberration of star light is pre-computed in the star tables in the Nautical Almanac (see my post from 12-30-2004 on sextant science). If you were travelling at 90% of the speed of light towards Orion's belt, for example, the angle between Polaris and the belt would be only 26 degrees (it's usually 90!) due to aberration.
    "How will we correct sightings for light being bent around black holes?"
    You have to get really close to a black hole before this is an issue. But astronomers can and do correct for gravitational deflection of light on a routine basis when they need to. The European Hipparcos mission carefully measured the exact positions of thousands of stars. Deflection of starlight by the Sun's gravitation was an issue at angles up to 90 degrees away from the Sun and even the deflection by Jupiter's much weaker gravitational field had to be taken into account. But gravity, even relativistic gravity, is really very simple and predictable. Lucky for us.
    42.0N 87.7W, or 41.4N 72.1W.
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