Light years to parsecs conversion example Of course, using our pc to ly converter above is much easier. See the example below for a detailed calculation. Knowing that 1 parsec equals 3.26 light-years, to convert from pc to ly one needs to divide the measurement in parsecs by 3.26 in order to get the light-years equivalent. It can be argued that the light year is therefore a more suitable unit for distances on the astronomical scale. ![]() On the other hand, light years express the distance covered by light in one year's time and while a year is an Earth-based time slice, it does not depend on other quantities except for the speed of light which is a universal constant. This makes it ill-suited as a universally applicable unit. One is the radius of our planet's orbit and the other is the choice to divide a circle in 360 degrees. The parsec is defined as the distance at which a star will show an annual parallax of one arcsecond, meaning it is based on two arbitrary quantities, characteristic of an Earth-based observer. Parsecs were historically used because distances between astronomical bodies were measured using the trigonometric parallax method. Difference between Parsecs and Light years The international symbol for light years is "ly" whereas for parsec it is "pc" so using this notation 1pc = 3.26ly. With accuracy to six decimal places, one parsec is equal to 3.261563 light years. Difference between Parsecs and Light yearsĪpproximately 3.26 light years equal one parsec.there are about 8.32 “light-minutes” in one Astronomical Unit. One Astronomical Unit (1 AU) is the mean distance from the centre of the Earth to the centre of the Sun. The nearest large galaxy – M32, the Andromeda galaxy – is around 752 kpc from Earth, and the entire observable universe is around 28 billion parsecs (28 gigaparsecs or 28 Gpc) in diameter. Our galaxy, the Milky Way, is estimated to be around 27,000 parsecs (i.e. ![]() (Note that the Earth would move two arcseconds over the course of the year, at this distance, as the radius and not the diameter of the Earth’s orbit is used to define the parsec.) The radius of Earth’s orbit around the Sun (1AU, see below) would appear to subtend an angle of one arcsecond if you were a distance of one parsec away. 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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