Step 1
Grab the Polygon Tool (in the Rectangle Tool sub-menu - hold click over the Rectangle Tool) and click-and-drag on your canvas - don't release click yet! Now press the "Down" Arrow key to reduce the number of sides. Press until you get a triangle. Now hold the SHIFT key to make it in an orthogonal position. It should look like below.
Step 2
Let's fill it. Press SHIFT+X to switch the Stroke with Fill.
Step 3
Let's rotate it 90 degrees.
Grab the Selection Tool (V), select the triangle, then go near a corner transformation control until you see two arrows. Click and rotate it while holding the SHIFT key. Make it look like below.
Step 4
We'll resize it and stretch one of its corners.
Make it a lot smaller using the Selection Tool (V). Now grab the Direct Selection Tool (A) and select the right anchorpoint. Drag it to the left, then hold SHIFT key to do it horizontally. Use the Selection Tool (V) to resize it to fit your canvas: hold SHIFT key and drag the mid-point control.
Now duplicate this command by pressing CTRL+D.
Step 5
So far we've done a ray. For what we're about to do, we need a symmetric shape. First, let's use our canvas as reference, because the edges are "magnetic". Align our shape on horizontal axis with the canvas using the button below the menus.
Now copy it (CTRL+C) and paste it to front (CTRL+F). Go to Object > Transform > Reflect (CTRL+SHIFT+T) and set it to Vertical at a 90 degrees Angle.
Step 6
Align this shape on the horizontal axis with the canvas. Now drag it horizontally using Selection Tool (V) and holding SHIFT key until the thick sides of the shapes are aligned. It should look like below.
Step 7
Now we will merge the shapes together.
Select both shapes using the Selection Tool (V). Now go the Pathfinder window (Window > Pathfinder) and click the "Merge" button.
Step 8
Let's make this smaller.
Grab the Selection Tool (V), drag one of the mid-point controls and hold SHIFT key while dragging. Now open the Brushes window (F5) and drag our shape into it. Make it a "New Art Brush".
Step 9
So far we created a simple brush for our rays. Now we'll create the actual rays.
Select the Line Segment Tool (). Now your dexterity will come in handy. Hold the ALT+SHIFT+Tilda (`) keys and click-and-drag a desired distance. Then release the SHIFT key and draw a rounded shape/spiral with your mouse. Do not even try to make it perfect. Try to vary the speed of your mouse cursor. Then click the brush you just created. Use the Selection Tool (V) to select the extra ones and delete them. It should look something similar to the image below. Select all (CTRL+A). Go to Object > Expand, then Object > Path > Clean Up.
Step 10
Now we need to fit it into a nice shape. Draw a regular shape: square, rectangle, oval, circle, hexagon.., your choice and place it over our shape. We'll use it as a clipping mask.
Remove the Stroke and the Fill. Now select all (CTRL+A) and right-click > Make clipping mask. And that's it!
