![]() "The distance at which an object has a parallax of one arc second."Īn arcsecond is equivalent to 1/3600 of a degree, that is an angle of one second of arc (") is equal to one sixtieth of one minute of arc ('), and one minute of arc equals one sixtieth of a degree.ġ parsec = 3.26 light years = 3.09 x 10 13 km = 206 265 AU Since stars are distant, the parallax angle is very small and is usually measured in arc seconds (fractions of a degree) rather than degrees. The Tycho Catalogue - detailed distribution and data map of a further 1.2 million stars.The Hipparcos Catalogue - 120 000 stars to a precision 200 times better than any previous observations.As a result of the mission two catalogues of observations were produced: Launched in 1989 the ESA Hipparcos mission used the parallax method to observe positions of stars within the galaxy. Astronomers use this effect to measure the distance to stars by determining the angle between the lines of sight of a star from two different positions of the observer. This apparent movement is known as parallax. ![]() If you hold one finger at arm's length in front of your face and close each eye in turn, you will see that the finger appears to move compared to distant objects behind it. Astronomers use many different ways to determine just how far away a star is. Furthermore, how bright a star appears is ultimately no indication as to how close it is to us. ![]() Although the stars we see with the naked eye look similar in size, they vary enormously in their distance from the Earth. On a clear, dark night we may be able to see a few thousand stars in the sky, a tiny proportion of the billions of stars that are thought to exist in the Milky Way alone. ![]()
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