Luke indicates that the ascension took place in Bethany.There are 10 kinds of atheists in the world*: there's the humble, friendly kind of atheist who simply does not believe in God, and then there's the kind who feels the need to frantically page through his parents' bible looking for contradictions**. This contradiction is actually a rather comical one, because it so cleverly combines a number of easily falsifiable assertions in a single-serving, ready to microwave package.
Acts says the ascension happened at the Mount of Olives, which it erroneously claims is a “Sabbath day’s journey” from Jerusalem one way. The Mount of Olives, which is still there today, is on the east side of Jerusalem and is a relatively short journey, even taking into account the boundaries of first-century Jerusalem...
The only two accounts we have of the event, which, ostensibly, were written by the same man, contradict each other on every important point...
The first error is in the assertion that there's some sort of contradiction between Bethany and the Mount of Olives. But a quick check of any map (here's the one from bibleatlas.org) will show that Bethany itself is right next to the Mount of Olives. In fact, it's so close that the Catholic Encyclopedia says that biblical (as opposed to modern) Bethany is "a village at the second milestone from Aelia [Jerusalem], on the slope of the Mount of Olives." Bethany is not only near the Mount of Olives, it's on the mount. So to complain that these two statements contradict each other is like saying a man could not have gone to Sacramento because he clearly says he went to California.
But for the record, Luke does not say that ascension took place "in Bethany," which would be rather odd for a private ascension party anyway, but "as far as," or as the Bible in Basic English*** aptly puts it, "near Bethany." So why doesn't Luke use the same word in both places? Luke likes to mix it up, I guess****. Besides, Luke said 5 chapters earlier that "And it came to pass, when he was come nigh to Bethphage and Bethany, at the mount called the mount of Olives..." Apparently he figured his readers were paying attention.
But the funny part is the author's assertion that Luke "erroneously claims" the mount is a Sabbath day's journey when, in fact, it is "a relatively short journey" from Jerusalem. This is why I seldom give atheist bible critics the benefit of the doubt: they take the Bible too literally. A "sabbath day's journey" is a figure of speech, which means just over a mile. That's a relatively short journey in my book. To take it literally is like asserting that "a hop, skip, and a jump" is about 8 feet, rather than the indeterminate but short distance that the phrase is used to denote.
Luke in both cases said they went up on the Mount of Olives toward Bethany, pretty close by Jerusalem, and there Jesus ascended. He didn't say it the same way twice - Luke seldom says anything the same way twice. But that's only a contradiction in the minds of those desperately searching for one.
* those who do binary and those who don't.
** Or more likely, loopholes.
*** A version that would certainly be burned by some folks in North Carolina.
**** If you don't get JSTOR, just know that it's an article from the Harvard Studies in Classical Philology that notes that while "the uniformity of [Luke's] style is one of its striking characteristics," this uniformity "is accompanied by great variety within the similar phrases, by a manifest fondness for change of expression, and by a notable copiousness of vocabulary in the terms used for things and actions often mentioned." I would add places to that list.