I found this wonderful definition on Wikipedia:
"Because the Earth's axis (see axial tilt) is tilted relative to the ecliptic, the twelve signs do not take the same amount of time to cross the eastern horizon. At the equator, there is very little difference (Pisces, Aries, Virgo and Libra take slightly less time than the other signs) but as one moves from the equator, larger and larger differences emerge.
In the northern hemisphere, the signs of Aquarius, Pisces, Aries, Taurus and Gemini take much less time than the theoretical two hours to cross the eastern horizon, whilst the signs of Cancer, Leo, Virgo, Libra, Scorpio and Sagittarius take much longer than two hours to do so. For example, at the latitude of Paris, France:
Pisces, Aries and Gemini take only about fifty-five minutes to cross the eastern horizon (this is referred to as the length of ascension or simply as the sign's ascension)
Aquarius and Taurus have an ascension of only about seventy minutes
Cancer and Sagittarius have an ascension of around two and a half hours
Leo, Virgo, Libra and Scorpio have ascensions of around two hours and forty-five minutes
At higher latitudes, these differences become even more marked. At the latitude of St. Petersburg, Russia:
Pisces and Aries ascend in only thirty minutes
Aquarius and Taurus ascend in only forty-five minutes
Capricorn and Gemini ascend in an hour and a half
actually individual degrees near Sagittarius or Cancer ascend twice as slowly as those near Aquarius or Taurus
Sagittarius and Cancer ascend in two hours and forty minutes
Leo, Virgo, Libra and Scorpio take as much as three hours and fifteen minutes to ascend."