3 Mapping the night sky
With so many objects in the night sky, it will be useful to have a way of locating individual objects and describing where a particular object can be found.
This can be done using a coordinate system. You will probably be familiar with this idea when navigating on the ground where map coordinates or latitude and longitude can be used to specify a unique position on a map or on the Earth’s surface.
Celestial coordinate systems work on a similar principle, but also need to take account of the apparent motion of the night sky caused by the rotation and orbital motion of the Earth.
The apparent motion of the northern night sky seen above the PIRATE telescope. As the Earth turns on its axis the sky appears to rotate about the north pole star. This time-lapse sequence was shot over a period of three hours.