Usual Astronomical Measure Units

The Light-Year. 1 light-year is 5,880,000,000,000 miles, 5,880 billion miles or 5.9 trillion miles (9,463 billion km). One light-year is the distance the light scours during one year. The speed of light is 186,000 miles per second -300,000 km per second- (671 million miles per hour). This measure unit gives somehow an historical view about the Universe: when a star is said located at 300 light-years, this means that it is seen as it was 300 years ago, i.e. about the year 1700; when a galaxy is at 4 million years, it is seen it as it was 4 million years ago, at the time when first men appeared

The Astronomical Unit (AU). 1 astronomical unit is the mean Sun-Earth distance, 149,597,870 kilometers (92,960,116 miles). One light-year is 63,240 AU

The Parsec. The parsec is the distance of an object having a parallax of 1 arc second: 3.26 light-year; 1 kiloparsec (kpc) is 1,000 parsecs; 1 megaparsec (Mpc) is 1 million parsecs. 1 light-year is 0.3069 parsec