It is the distance that light travels in a vacuum in one Earth-year, which equals 9.46 trillion kilometers (5.88 trillion miles). How far is a light-year?ĭespite its name, a light-year is a unit of distance, not a unit of time. For example, at their closest to the Earth, Mars and Jupiter are 0.37 AU and 3.9 AU away from it, respectively. The astronomical unit is commonly used to measure distances between objects within the Solar System or around other stars. As the Earth’s orbit is elliptical, our planet’s actual distance to the Sun varies by about 3% around the year – that’s why the average distance is used.
One astronomical unit (AU) is the average distance from the Earth to the Sun, which is about 150 million kilometers (93 million miles). For example, the asteroid 2001 FO32, which flew by the Earth in March 2021, was five lunar distances away from us. Lunar distance is mainly used to express the distance to near-Earth objects, like asteroids and comets.
At an average perigee (the closest point to the Earth), the Moon is 363,228 kilometers (225,700 miles) away from our planet, and at an average apogee (the farthest point from the Earth), it’s 405,400 kilometers (251,900 miles) away.
Why is the average distance used? As the Moon’s orbit is not perfectly circular, our natural satellite is not always the same distance from the Earth. For reference, this equals about 30 diameters of the Earth. In astronomy, lunar distance (LD) is the average distance from the center of the Earth to the center of the Moon, which is 384,400 kilometers (238,855 miles). What’s bigger: lunar distance, astronomical unit, or light-year? How are these units used? Check out our infographic to find these out! See Infographic What does lunar distance mean?