Combustion
A planet is combust when it sits within 8°30′ of the Sun, close enough that the Sun's light swallows it. It can't be seen and it can't act freely — though in the right chart that same closeness is the thing being asked for.
The fuller picture
Combustion is one grade of a three-step ladder measured from the Sun, and the ladder is easier to hold in mind than the individual terms. A planet more than seventeen degrees away is free of the Sun and behaves normally. Inside seventeen degrees it's under the beams — dimmed, working at a disadvantage. Inside eight degrees and thirty minutes it's combust, which is a serious affliction. And then, within seventeen arcminutes of the Sun's exact degree, it flips: that's cazimi, the single strongest fortification on the board. These three figures form William Lilly's own coherent ladder on Christian Astrology p.113, and they are the figures iHorary now uses.
What combustion does is hide a planet rather than destroy it. Think of a star lost in daylight — still there, still moving, invisible. Read on the person asking, it describes someone who can't see their own situation clearly and can't act freely within it; read on the thing asked about, it describes a matter obscured, overwhelmed, or hidden from view. It's routinely ranked with the worst things that can happen to a planet by position, alongside being retrograde and being stuck in one of the weak houses, and a planet that's combust and closing on the Sun is going from bad to worse.
Here's the distinction a short definition can't carry, and it's the one worth the page. Combustion isn't automatically bad news, because sometimes combustion is the answer. Take a love question with Aquarius rising: Saturn rules the ascendant and stands for the person asking, and the Sun rules the seventh and stands for the other party. If the Sun applies to Saturn, then the person asking is about to be made combust — and that combustion is itself the union perfecting. The very configuration that would ordinarily describe someone overwhelmed and unable to act is, in that chart, the thing they came to ask about arriving. Nothing in the mechanics changed; what changed is what the contact means once we know who each planet stands for.
Two more distinctions in the same family. Applying to combustion and separating from it are different states, and the difference matters: a planet moving out of the Sun's rays at nearly six degrees and widening has been through something, while a planet three degrees out and closing is walking into it. And the distance is measured properly — a planet at eight degrees and forty-five minutes from the Sun is under the beams, not combust, which sounds like pedantry until you notice it's the whole difference between a serious affliction and a mild one.
One last thing: combustion doesn't settle a chart by itself. It's grave testimony about the condition of one planet, and grave testimony still has to be read against everything else in the figure — the contacts, the receptions, the houses. Lists of afflictions that include combustion as one item among five are especially treacherous: they fire easily, and a careful astrologer will regularly read the chart the other way after looking at it whole. Combustion of the ruler of the person asking is the one classical caution genuinely worth leaning on, and even that's a strong inclination towards a negative outcome rather than a rule that decides the question before the chart has been read.
In your chart
Every planet's distance from the Sun is measured and labelled in the instrument — Free of the beams, Under the beams, Combust or Cazimi — with the exact separation in degrees and minutes beside it, so you can see how far a planet is from the next boundary rather than just which side of it it lands on. A combust planet also carries a Combust chip among its condition chips, with the score that condition contributed to its total, though the chip names the planet rather than the actor it stands for — for that, read the significator list, which says which planet carries you and which carries the matter. The radicality worksheet carries a dedicated check on whether the ruler of the ascendant is combust, and cazimi passes that check rather than failing it. Where a significator is combust, iHorary records it as critical evidence and will name it as the load-bearing testimony behind the answer it gives.
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