Any planet in the eastern section of a horoscope is said to be ascending, i.e., moving toward the Midheaven. The term is usually reserved for those planets in the fourth quadrant rising from Ascendant to Midheaven.Due to the obliquity of the ecliptic, some signs rise over the horizon faster than others.
Here the Ascension is said to be long or short as the case may be. An 'Ascending planet' or 'rising planet' is one which is conjunct the ascendant. The 'ruling planet' is the planet which rules the sign of the Ascendant.
Planets can assume added importance in the birth chart due to their relationship to the ascendant.The planet that rules the astrological sign of the ascendant is called the chart ruler, and is said to be of particular importance. So for example, if the ascendant sign is Libra, Venus will be the chart ruler. Also the e planet nearest the ascendant in the first house is usually called the rising planet and has a particular importance in the chart. However, if a planet in the twelfth house is very close (within one or two degrees) to the ascendant, then it can be taken to be the rising planet instead. If a planet is actually in conjunction with the ascendant it then becomes vitally important in its effect on the personality.