Astrometry is the astronomical measurement of positions (positional astronomy) and motions (dynamical astronomy). It is very important to know how objects in the universe are moving—or, conversely, not moving. Astrometry of near-Earth asteroids, for example, can help us determine if any objects in the solar system are likely to strike our planet. Astrometry of stars helps us understand how our solar system moves within the Milky Way galaxy. Furthermore, astrometry is very important in establishing reliable frames of reference, in time as well as space, for both scientific and everyday use. The United States Naval Observatory, for example, continually measures and records the movements of the Sun, Moon, planets, and stars; the data is passed on to the Nautical Almanac Office, which, together with the British government, publishes the Astronomical Almanac. This annual almanac is used as a daily reference for navigation, surveying, and science.