![]() Note that all stars are further than one parsec from Earth, and Proxima Centauri – the nearest star to Earth – is around 1.3 parsecs away.Īn alternative way to picture this, is to imagine you are looking back at Earth from deep space. In other words, if there were a star located exactly one parsec from Earth, it would appear to shift in position around a fixed point against the distant background stars by two 3,600ths of a degree (two arcseconds), and back again, over the course of a year, due to the motion of the Earth around the Sun. The word parsec is a contraction of the words “parallax of one arcsecond”, since a parsec is defined as the distance from Earth that a star would need to be in order to exhibit an annual parallax of 1 arcsecond. ![]() The ParsecĪ parsec is a unit of distance used by astronomers, which is equivalent to around 3.26163344 light-years. The observable universe is about 91 billion light-years in diameter (534,943,482,710,000,000,000,000 miles), at the present time, although the size of the entire universe is unknown. Proxima Centauri our nearest star (other than the Sun), is approximately 4.243 light-years away. ![]() 5.87849981 x 10 12 miles, or roughly 6 trillion miles. Since light travels at a constant speed, in a vacuum, of around 3 x 10 8 metres per second (or, more precisely, around 299,792,458 metres per second), a light-year is around 9.4605284 x 10 12 kilometers – i.e. One light-year is the distance that light travels in a year, through the vacuum of space.
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