Where does Europe end?

This is either a very simple question or a very difficult
question -- depending on if we are talking about physical or cultural
borders.

Physically, there is no reason to call Europe a
separate continent (separate from Asia).  However, there is a commonly accepted
definition of Europe that says it is separated from Asia
by

readability="3.8903225806452">

the href="http://en.wikipedia.org/wiki/Water_divide">water divide of the title="Ural Mountains" href="http://en.wikipedia.org/wiki/Ural_Mountains">Ural
Mountains, the href="http://en.wikipedia.org/wiki/Ural_%28river%29">Ural River, the title="Caspian Sea" href="http://en.wikipedia.org/wiki/Caspian_Sea">Caspian
Sea, the href="http://en.wikipedia.org/wiki/Caucasus">Caucasus region ( title="Borders of the continents"
href="http://en.wikipedia.org/wiki/Borders_of_the_continents#Europe_and_Asia">Specification
of borders) and the href="http://en.wikipedia.org/wiki/Black_Sea">Black Sea to the
southeast.

Culturally,
it is much harder to define where Europe ends.  This is especially true in modern times
when the influence of Europe has spread so far and European peoples have colonized the
Americas and Australia and New Zealand.  There was a time when Europe was defined as
pretty much the same thing as Christendom, but Christendom and Europe are no longer
geographically the same thing (or anywhere near it).

I do
think that most people would still define Europe (culturally) as the lands that have
been Christian since before the Renaissance.  This means that Europe would include
Russia and Romania but also Iceland and England.  This is not a perfect definition, but
I think that it captures how most people think about Europe.