A gigameter (Gm) is a unit of length in the metric system, equal to one billion meters. It is often used in scientific contexts to measure large distances, such as those found in astronomy. For example, the distance between celestial bodies can be expressed in gigameters to simplify calculations. In terms of scale, one gigameter is equivalent to 1,000 kilometers or about 621 miles. This makes it useful for expressing distances within our solar system, such as the distance from the Earth to the Sun or between planets like Mars and Jupiter.