What ISO should I use ?

[cpper]

Hello

I own a Canon soap dish, model A590 IS. I want to photograph some shooting(falling)stars and satellites. Yes,I know, my camera isn't for that. But my question is: What ISO should I use to photograph them ?

I will attach 4 images, all taken 15sec. exposure time ,with ISO 100/200/400/800.

What ISO is the best to "catch" shooting stars and satellites considering the images ?

Please give me your advice,thanks in advance

ISO 100

ISO 200

ISO 400

ISO 800

[Leveye]

15 seconds either 400 or 800

[JKB]

2nd either 400 or 800 depending on the sky condition/light pollution etc.

Cheers

[bogdog]

for me.. i say the 200 is better picture

because of the pollution from the buildings lights the higher iso gave way more noise,would be better to have went to a dark place