Every year Pi () day is celebrated on the 14^{th of} March, allowing people throughout the world to throw a party for this superstar number. The reason that Pi Day falls on the 14^{th} of March is because the date of (3.14) can be written as the first three digits of Pi when following the U.S. convention of (month/date). If you want to celebrate by decorating your classroom, office or even living room, then make this super easy Pi Day Sphere Bunting.

## How To Make a Pi Day Sphere

Watch the video or read through the steps below.

### Step 1

Draw 10 identical circles by using a pair of compasses or by drawing round a circular object. Alternatively print off this Pi Day Sphere Worksheet which can be used in the classroom or at home. The sphere in the worksheet has a diameter of around 5cm, but you can make your spheres as big as you like. Decorate the circles to celebrate Pi Day. Your imagination is the only limit!

### Step 2

Cut out the decorated circles.

### Step 3

Fold each circle in half, with your design on the inside of the fold.

### Step 4

Take a circle and put glue on one half of the undecorated side. Stick this glued half to an undecorated half of a different circle. (You are never putting glue on your decorated sides!)

Continue gluing the undecorated halves of different circles together, creating a fan effect. Do this until you only need to glue one final side.

### Step 5

At this stage add a string down the middle of your sphere and glue the final sides together. Your Pi Day Sphere is complete! If you are a teacher with a class of 30 pupils, you should now have enough spheres to string together to make some impressive looking bunting.

## Other Ideas for Your Pi Day Sphere Craft

- You don’t have to use 10 circles; you could combine different numbers of circles and see what works best.
- Experiment using different colours of paper.
- Use your paper sphere as a handy revision guide – write a key fact on each circle and then leaf through it like a book.
- Keep your Pi Day sphere to hang on your Christmas tree.

## Handy Facts About the Sphere

Here are 10 handy facts about spheres to think about while you are making your Pi Day Sphere craft.

- A sphere is the set of points that are the same distance from a point (known as the centre) in 3-dimensional space.
- The volume of a sphere with radius is .
- The surface area of a sphere with radius is , a formula which was first found by Archimedes.
- The sphere has the lowest surface area to volume ratio of any solid shape. This means that for a given volume, a sphere has the least amount of surface area possible.
- This special surface area property means that lots of spheres appear in nature – bubbles are spherical because they need the smallest possible surface area to get the lowest amount of surface tension.
- A hemisphere is exactly half of a sphere.
- A sphere only has one surface and no edges or vertices.
- A sphere with centre and radius has the equation .
- Planet Earth is a Spheroid, which means that it is not quite a sphere.
- Here is a picture of Einstein reflected in one of the most accurate spheres ever made. It only differed from being a perfect sphere by the size of 40 atoms.

Article by Hazel Lewis