Full Idea
Subjective probability measures a person's strength of belief in the truth of a proposition; objective probability concerns the chance a certain sort of event has of happening, independently of whether anyone thinks it is likely to occur or not.
Gist of Idea
Subjective probability measures personal beliefs; objective probability measures the chance of an event happening
Source
Alexander Bird (Philosophy of Science [1998], Ch.6)
Book Reference
Bird,Alexander: 'Philosophy of Science' [UCL Press 2000], p.188
A Reaction
The challenge to the second one is that God would know for certain whether a meteor will hit the Earth next week. The impact looks like 'bad luck' to us, but necessary to one who really knows.