Sin and Cos are a programmers best friend!  I was looking at other games for inspiration and I saw this image from r-type

A circle of aliens spins around the player and you have to shoot them from the inside.

To calculate the points of a circle is quite easy, the calculation is - 

    x=(radius*cos(angle))
    y=(radius*sin(angle))

Therefore I have an array of 10 objects which is calculated as follows - 

    cx=(230*cos(i*36))
    cy=(230*sin(i*36))

230 pixels from the 'origin' and I have 10 objects - 360/10=36. I is incremented by 1 each step.

I now have a nice circle of aliens, I can increase the number by reducing the number 36.  I can make the circle smaller or larger by increasing the radius.

The first level is more or less complete, with boss monster at the end.  On to the second level!