![]() ![]() ![]() The Hipparcos satellite was able to measure distances to stars up to a few hundred parsecs (say, 1500 light years) away. With a base to the triangle of 3×10 11 m, given sufficient accuracy of measurement, objects that are extremely far away can have their distance accurately determined. The actual elliptical nature of the Earth's orbit must be taken into account, of course.Īt the distance (d) at which the angle γ becomes 1 arcsecond (1 degree = 3600 arcseconds), d is said to equal 1 parsec (roughly 3.26 light years.) Astronomers generally prefer to work with parsecs rather than working with light years. ![]() In this case ||A-B|| is the average distance between the Earth and the Sun this is one astronomical unit (AU), or roughly 146 million kilometers. Multiple measurements are made for two reasons: firstly, to allow the distance to be calculated more accurately and secondly to prove the star does not move radially, relative to our solar system (this is the case if the same distance is found every cycle.) Half a year after that a third measurement will be made, and this cycle is repeated at half-yearly intervals. The first measurement will be made on this day.Įxactly half a year later the second measurement will be made. First, one must choose a day on which the star- Sun-Earth angle is roughly ninety degrees. A star's motion relative to our solar system must be established by observing it at the same time each year. ![]()
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