More to the point for purposes of astronomy, the meter is awkwardly small for measuring distances within the Solar System. The meter is even more awkwardly small for measuring distances between stars. The distances between stars are much greater than the size of the Solar System. The basic unit of time in the metric system is the second . The other frequently used unit of time is the year , the time it takes the Earth to revolve once around the Sun.
Astronomers use seconds to measure short periods of time.
For instance, an Astronomy 161 lecture is 2880 seconds, or 48 minutes long. For longer periods of time, years are a more convenient unit. The basic unit of mass in the metric system is the kilogram , equal to the mass of water contained within a cube 0.1 meters on a side. A one-liter bottle of water has a mass of 1 kilogram. At the surface of the Earth, if I hold a 1-kilogram mass, gravity will pull it towards the Earth's surface with a force of 2.2 pounds, or 35 ounces.