占星学专业领域中，所谓的相位（aspect）是指星盘中所显示出行星彼此之间所形成的一个角度（angle），同时也包含四大尖轴：上升点（ascendant / Asc）、天顶（midheaven / Mc）、下降点（descendant / Des）、天底（lower midheaven or Imum coeli / Ic），以及其他占星学所关注的交点。从地球上来看，相位是星空中的两个行星之间在黄道的度数与分钟上经由测量出的角距离。根据占星学的传统，祂们表示对于地球上人们生活及事务时机的转变与发展上的变化。

In astrology, an aspect is an angle the planets make to each other in the horoscope, and also to the ascendant, midheaven, descendant, lower midheaven, and other points of astrological interest. Aspects are measured by the angular distance in degrees and minutes of ecliptic longitude between two points, as viewed from Earth. According to astrological tradition, they indicate the timing of transitions and developmental changes in the lives of people and affairs relative to the Earth.