入相位和出相位是古典占星的重要概念，也是非常实用的解盘技术，尤其在主限法、行运、次限等推运技术当中有重要的运用，现代占星很难见到。
什么是入相位？
简单来说，行星沿着黄道十二星座按次序运行，运行周期快的行星会逐步接近（applying）运行周期慢的行星。仍在形成过程中的相位，也称为入相位(application)。
这意味着两颗行星中速度较快的（或ASC/MC等点）行星正在接近速度较慢的行星并最终形成精确相位。与之相反的是出相位(Separating)，即已经超过了精确度数的相位。在这种情况下，行星正在远离。
因此识别入相位和出相位，就需要清楚行星沿着黄道的运行速度，下表的行星运行周期需要熟读成诵：
月亮：29.53个地球日
水星：87.97个地球日
金星：224.7个地球日
太阳：1个地球年
火星：1.88个地球年
木星：11.86个地球年
土星：29.46个地球年
天王星：84.81个地球年
海王星：164.8个地球年
冥王星：248个地球年
入相位为什么这么重要？
我们来介绍下古典占星中关于入相位的一些规则：
1.入相位比出相位更强有力，更吉或更凶。
Applying configurations were thought to be more powerful than separating configurations, for better or worse.
2.入相位表示将来会发生的事件和情况，出相位表示过去已经发生的事情。因为入相位持续形成并趋向精确度数相位，而出相位已经形成并驱离精确度数相位。
Applying configurations were thought to indicate events and circumstances that will develop in the future, while separating configurations indicate things that have already occurred in the past. This is because applying aspects are planetary configurations that are still forming or moving towards being exact by degree, while separating aspects represent configurations that have already completed and are now moving away from the exact, degree-based alignment.
3.月亮等重要星体与吉星形成入相位时是积极的，而月亮等重要星体与凶星形成入相位则是消极的。
This leads to the concrete interpretative principle that the outcome of any inception that is initiated when important planets like the Moon are applying to benefic planets will be positive, whereas if the Moon is applying to malefics the outcome will be negative.
4. 行星越接近精确度数相位，则他们的关系将更强烈或尖锐。因此入相位和出相位适用于行运(transits)。除了月球是13度外，行星之间以度数相位最重要或最强烈的范围是在3度以内。
The closer that the planets get to an exact, degree-based aspect, the more intense or acute their relationship becomes.This also applies to transits, as a transit begins as soon as the planets become configured by sign, but grows more intense the closer the transiting aspect gets to completion. Applying within three degrees is the most important or intense range for degree-based aspects between planets, except for the Moon, which is thirteen degrees.
Tips：入相位在古典占星中频繁用到，因此一定要练习入相位的识别，熟练到一眼看出星盘中哪些相位是入相位的程度！