i know it measured 118,000 stars up to 1/1000 parsecs because it got above the blurring effect of the atmosphere, but how much farther away than earth could it probe these stars? and how?|||Hipparcos' mission was to determine the positions of selected stars as accurately as possible using trigonometric parallax. The orbit of the earth around the sun causes nearby stars to appear to shift back and forth against the background of more distant stars and galaxies, and the amount of shift is proportional to the star's distance from the earth. At a great enough distance, a star's parallax shift becomes much smaller than the apparent diameter of the star itself and cannot be accurately measured. The upcoming Gaia probe, scheduled for launch in 2011, is expected to measure the parallax of stars tens of thousands of light-years from earth.|||The Hipparcos (not Hipparchos) satellite has a pointing resolution of 0.001 arcsecond. It can "see" as far as any good professional telescope: 13 billion light years, more or less. That is to say, to the edge of the visible universe. But the main mission was not to see far, it was to see their positions accurately.
It takes very advanced methods for ground based instruments to get 0.01 arcsecond pointing. Hipparcos was 10 times better.
It's not that the "blurring" is so bad, its the twinkling the makes the star image move around.
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