The Pentagram
The Pentagram (or Pentangle) is a 5pointed star. You may think it has something to do with witchcraft, but in fact it is more famous as a magical symbol and is also a holy symbol in many religions. In fact, this simple figure is quite amazing. 
Inside a Pentagram is a Pentagon 
You can make a pentagram by first drawing a pentagon, then extending the edges.  
Or by drawing lines from corner to corner inside a pentagon. 
Ratios
But the pentagram has a special number hidden inside called the Golden Ratio, which equals approximately 1.618
When I drew this, I measured the 4 lengths and I got a=216, b=133, c=82, d=51. So let's check to see what the ratios are:
If I had drawn and measured more accurately, I would have been even closer! 

Why not have a go yourself:

Irregular PentagramSo far we have only been looking at the regular pentagram (all sides and angles equal), but there are also irregular pentagrams. 