First: what synastry even is
Synastry is what happens when you lay two birth charts on top of each other and look at the angles between the planets. Your Venus to their Mars. Your Moon to their Saturn. Those angles — called aspects — are the wiring of the connection. You're not reading one person; you're reading the current that runs between two.
The five aspects that carry the most weight
Ignore the noise and look for these. Sun–Moon (do you feel like home to each other). Venus–Mars (the raw attraction). Moon–Moon and Moon–Venus (emotional safety). Saturn touching a personal planet (the weight, the lessons, the 'why does this feel so serious'). Mercury–Mercury (whether you actually talk the same language). Five aspects will tell you more than a hundred.
Know your angles: the good, the spicy, the heavy
Trines and sextiles flow — easy, supportive, sometimes lazy. Squares and oppositions create tension — friction that's either chemistry or a recurring fight, depending on the planets. Conjunctions intensify whatever they touch. A square between Venus and Mars is electric and exhausting. A trine between Moons is a soft place to land. The aspect tells you the flavor; the planets tell you the topic.
Read the red flags on purpose
The hard aspects aren't reasons to run — they're the places the connection will ask the most of you. Saturn to the Moon can feel like love that also feels like homework. Mars square Mars is great sex and bad fights. Naming the hard aspect out loud is half of defusing it. The chart doesn't decide; it shows you the pattern so you stop being surprised by it.
The 60-second version
Find the Sun–Moon and Venus–Mars connections (chemistry and care). Note any Saturn aspects (weight). Check the Moons (safety). Glance at Mercury (communication). Then ask the only question that matters: does the chart describe a pattern you want to live inside? That's the whole read. House Seven does all of this for you and writes it in plain language — but now you can do the napkin version yourself.