Units of measurement
When we refer to various astronomical phenomena probably we touch in contact with problems related to the measurement of Time and Space, and the use of common units that we use in our daily lives can not be applicable to astronomical facts.For example, we could express in kilometers the distance between Pluto from the Sun (about 5.9 billion km on average), but this amount of kilometers so large makes us to be uncomfortable to work with this unit.
So is useful to use other kind of units of measurement.
As we can read in the wikipedia :
So is useful to use other kind of units of measurement.
As we can read in the wikipedia :
- An astronomical unit is a unit of length now defined as 149,597,870,700 metres. The astronomical unit was originally defined as the length of the semi-major axis of the Earth's elliptical orbit around the Sun, and its useful to refer to the distance between the planets in our solar system and the Sun
- A light-year, also light year or lightyear, is a unit of length equal to just under 10 trillion kilometres. As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in a vacuum in one year. The light-year is mostly used to measure distances to stars and other distances on a galactic scale, although the preferred unit in astrometry is the parsec (approximately 3.26 light-years), because it can be more easily derived from, and compared with, observational data. Note that the light-year is a measure of distance (rather than, as is sometimes misunderstood, a measure of time)