eyeofmidas.com/htdocs/js/star.js

function Star() {
	var x = 10, y = 10, diameter = 3, mindiameter = 0.1, maxdiameter = 3, height = 10;
	var pulse = 0.1;
	this.init = function(canvas) {
		x = Math.floor(canvas.width * Math.random());
		y = Math.floor(canvas.height * Math.random());
		diameter = 2 * Math.random() + 1;
		pulse = (10 * Math.random() + 1) / 1000;
		mindiameter = Math.random();
		maxdiameter = 2 * Math.random() + 1;
	};
	this.update = function(canvas) {
		diameter *= 1 + pulse;

		if(diameter > maxdiameter) {
			diameter = maxdiameter;
			pulse *= -1;
		}
		if(diameter < mindiameter) {
			diameter = mindiameter;
			pulse *= -1;
		}
	}, 

	this.draw = function(context, offset) {
		context.beginPath();
		context.arc(x + offset.x, y + offset.y, diameter, 0, 2 * Math.PI);
		context.fill();
	}
}