Episode 96. You know what aspects are. They're the angles the planets make to each other and can impact how they interact. For example, two planets that are 90º apart are in a square - and this indicates tension. So what are astrologers talking about when they mention applying and separating aspects?
An aspect is applying when the faster-moving planet is heading toward the slower-moving planet and closing in toward the exact orb. It's intense. I liken it to "crowning" - the period before the baby is born. You can feel it, you know it's coming, and you have to brace yourself. It's the buildup before the grand finale.  For applying aspects, the tendencies are magnified. 
Separating aspects occur when the faster-moving planet is moving away from the exact orb of the aspect made to that slower-moving planet. The energy here is like the birth has happened, now we're adjusting to our new life, and perhaps feel a sense of relief.
Learn more in this short episode.