Observing the Night Sky

Navigating the Sky

When observing the night sky, you need to know how to navigate…

You need a map, in this case a star map...

The Constellations

The ‘patterns’ on the night sky that we use to navigate are known as Constellations.

There are 88 constellations, covering the complete sky. Most of the constellations in the northern hemisphere were named by the ancient Greeks matching characters from their mythology...

2D to 3D Constellations

We see the stars on the ‘flat’ sky above us, but these stars are actually spread throughout 3 dimensional Space.

The video below shows the constellation of Orion in 3D:-

Distance Scales

We can use ‘scale factors’ to represent relative distances in Space, for example:-

1 AU : 1 cm


1,000 ly : 1cm

The table below shows some example scaled distances that could be used to create a 3D model of the constellations of Ursa Major and Orion:-

The Apparent Motion of Stars

As the stars appear to move across the night sky as the Earth rotates, we need to find a fixed point to navigate from.

The image below is of a long exposure image, taken over several hours, showing the apparent motion of the stars:-

There is, however, one fixed point in the night sky, the Celestial North Pole. If you take a long exposure image, looking North. you can see that all the stars appear to rotate around this fixed point. The Star at the centre is the North Star - Polaris.

If you can find Polaris, you will be facing North and can navigate the night sky.

How to find the Celestial North Pole

From the edge of the ‘bowl’ of the big dipper, follow their line until you reach the ‘North Star’:-

Augmented Reality Planetarium

Obviously, it is not possible to observe the night sky during the day, but we can use augmented reality in order to 'see' the night sky. The following free app is very useful in doing this:-

How to use Star Walk 2

Click the Compass to start A.R.

Find Polaris then click for more information

Click on the plotting compass for data information

The video below shows a planetarium tour of the night sky:-