Editing Faster-than-light (section)

===Daily sky motion===
For an earth-bound observer, objects in the sky complete one revolution around the Earth in one day. [[Proxima Centauri]], the nearest star outside the [[Solar System]], is about four and a half [[light-year]]s away.<ref name="A2 Student Book">
{{cite book
|author=University of York Science Education Group
|year=2001
|title=Salter Horners Advanced Physics A2 Student Book
|publisher=Heinemann
|pages=302–303
|isbn=978-0435628925
}}</ref> In this frame of reference, in which Proxima Centauri is perceived to be moving in a circular trajectory with a radius of four light years, it could be described as having a speed many times greater than ''c'' as the rim speed of an object moving in a circle is a product of the radius and angular speed.<ref name="A2 Student Book"/> It is also possible on a [[geostatic orbit|geostatic]] view, for objects such as comets to vary their speed from subluminal to superluminal and vice versa simply because the distance from the Earth varies. Comets may have orbits which take them out to more than 1000 [[astronomical unit|AU]].<ref>
{{cite web
|date=15 April 1996
|title=The Furthest Object in the Solar System
|url=http://www.oarval.org/furthest.htm
|work=Information Leaflet No. 55
|publisher=Royal Greenwich Observatory
}}</ref> The circumference of a circle with a radius of 1000 AU is greater than one light day. In other words, a comet at such a distance is superluminal in a geostatic, and therefore non-inertial, frame.