Why would you want to sling at night? Because it would make perfect conditions to see how your projectile flies. Don't call me crazy just yet. All this talk about the way a projectile spins and curves got me thinking about how hard it can be sometimes to truely see with the naked eye. At night the background is all one color; black. I was thinking you could paint stripes or dots on a tennis ball with glow in the dark paint. Then charge up the paint really bright with a flashlight. When the ball is slung only the dots or stripes would be visible. This would give you a good idea of what your projectile really does. Plus it would look cool. Sling it high enough and peolpe might report UFOs. I will give it a go if I find the time. Glow in the dark paint can be bought at most craft stores.

It should not be that hard to find cuz tennis balls don't go far and they glow in the dark. Use one ball and keep a flashlite with you to charge up the paint

I've tried doing this before.

A few things I learned the hard way, hope their useful

1) A solution that will easily bleed through the felt, or can be easily sprayed on (Use a lot) works best
2) Use a ice chest with a light within to charge the balls, you can easily destroy your night vision otherwise.
3) Keep in mind that the balls actually fade from view very quickly as it travels further away from you.
4) There is generally a lot of ambient light which can make it harder to detect the soft glow of a tennis ball: Moon, stars, city lights etc.
5) Sling into flat areas that don't have deep depressions, or underbrush. (you would think you's see it)

jope that helps

-Unsapien

those who live near the seaside or a big lake could also try throwing some incendiary glands - http://slinging.org/36.html - into the water so that they wouldn't burn anything