What film speed should I use ?

In astrophotography I use a 3 inch refractor scope...a camera adaptor...a SLR camera. What film speed and camera speed and aperature should I use.

TMAX 400 is moderately fine grain and reasonably fast. (Black and White) ASA 400. You can push it to ASA 800 by giving it an extra 2 mins in developer. Exposure times depend on the object and the efective focal ratio of the rig.
Leave the camera lens wide open. Stopping it douwn will just reduce the field.
You can get a pretty good idea of the effective fr as follows:
Assuming 3 inch clear arpt. Take a picture of the moon. Doesn't need to be exposed well...Just so you can measure the disk image = d in inches:

fr = dX96/3 = 32d

working from the fr and the object look up optimal exposure times from the web.

There are a few answers:
1. The film speed is called its ISO or ASA. This is a number (100, 200, or 400) usually. The lower (100) number will have better results, but you'll need a longer exposure time or the picture will be darker. The higher (400) number won't look quite as good, but you'll be able to take your shot faster. I'd recommend trying 200 since it's in the middle and decide for yourself if speed or quality is more important.
2. The exposure time in seconds needs to be long enough to get a good picture. At low magnification, you might try starting out with a sixty second exposure and see what happens.

it depends on your camera and telescope, but I'd say a long term exposer, at least on the order of minutes, would be a good speed.

try difrent films

really fast film has bad reciprosity