Imagine if you could hold your index finger a mile away from you, the difference between where your left and right eye would see it is tiny – much less than you just experienced.Ĭoming back to the definition of a parsec, instead of our left and right eyes, astronomers use the opposite sides of Earth’s orbit around the sun to measure the parallax angle. The further away the object is, the smaller its parallax angle. The difference between your finger’s first and second position is its parallax angle. Your finger has ‘jumped’ to the right and is no longer in line with the distant object you chose. Now, close your right eye and open your left. Line it up with something in the distance, like the edge of a door. Hold your index finger out at arm’s length with your left eye closed. You can experience a parallax angle for yourself right now. That’s not a useful, everyday description, so let’s decode it a little.įirst of all, think of the ‘parallax angle’ part. One parsec is the distance at which a star has a parallax angle of 1 degree. Since miles and kilometers are tiny and not useful for cosmic scales, astronomers defined two new measurements to help us out: the parsec and the light-year for this purpose.īoth measurements define distance, although parsec is usually used for objects within our galaxy while light-years define larger distances. So many zeros do not usefully convey the staggering distance because, beyond a billion, they are like white noise – they don’t mean anything to us on an emotional level. If we were to use the same measurements for cosmic distances, the zeros would overflow our pages!įor example, the Andromeda galaxy is 21,000,000,000,000,000,000 km away, and it is just the nearest galaxy. We use miles and kilometers to define distances on Earth. The Parallax Method of Measuring Star Distance.How Do We Measure the Distance of Stars?.
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