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11 maj 2018 · The units of measurement we use to define distances on Earth prove inadequate to the task of reckoning distances in outer space. Standard astronomical measures include the astronomical unit and the parsec, with another unit, the light-year, is common in popular usage.
How do we know how far away objects are in space, and what units of measurements are used in astronomy for determining these distances?
To measure the distances between stars, astronomers often use light-years (abbreviated ly). A light-year is the distance that light travels in a vacuum in one year: 1 ly = 9.5 x 10 12 km = 63,240 AU. Proxima Centauri is the nearest star to Earth (other than the Sun) and is 4.2 light-years away.
Understand the importance of defining a standard distance unit; Explain how the meter was originally defined and how it has changed over time; Discuss how radar is used to measure distances to the other members of the solar system
Astronomical Unit, a measure of distance, based on the mean Sun-Earth distance. The International Astronomical Union defines the AU as the distance from the Sun at which a particle of negligible mass, in an unperturbed orbit, would have an orbital period of 365.2568983 days (a Gaussian year).
Light years. We need a different unit of measurement, because at these distances, kilometres are too small to be much use. One unit for measuring very big distances is the light year. This is the distance that light travels in a year, so 1 light year is about 9,500,000,000,000 km.
The most common measurement unit for astronomical distances is the light-year. The name often confuses people—remember that a light-year is a measurement of length/distance, not time. It means the distance that a photon of light can travel through the vacuum of space in one Earth year.
