How would I get a UNIX timestamp (number of seconds since 1970 GMT) from a Date object in a Rails app?

I know `Time#to_i` returns a timestamp, but doing `Date#to_time` and then getting the timestamp results in something that's off by about a month (not sure why...). 

Any help is appreciated, thanks!

Edit: OK, I think I figured it out- I was processing a date several times in a loop, and each time the date was moved a little because of a time zone mismatch, ultimately leading to my timestamp being a month off. Still, I'd be interested in knowing if there's any way to do this without relying on `Date#to_time`.