The one word substitution is Constellation.Orbit : an area of activity, interest, or influence.Solar system : the collection of eight planets and their moons in orbit round the sun, together with smaller bodies in the form of asteroids, meteoroids, and comets.Comet : a celestial object consisting of a nucleus of ice and dust and, when near the sun, a 'tail' of gas and dust particles pointing away from the sun.Constellation : Group of stars.