The geometry and how often it turns up
We allow seven degrees of orb for a trine. The Moon reaches a trine to any fixed point twice in each circuit, once on each side, so across a month there are two windows of roughly a day when the aspect is inside orb. Pluto is essentially stationary on that timescale, moving well under a degree in a day, so the Moon supplies all the movement.
Inside a one degree orb the window is a couple of hours. That difference is why two people born on the same date can have very different versions of the same listed aspect, and why the birth time matters more here than the birth date.
Trines also put the two bodies in signs of the same element in the usual case, which is where the older language about ease comes from. A trine that crosses a sign boundary breaks that, and it usually reads more weakly.
What the tradition reads into it
The Moon covers instinct, memory and the way a person settles. Pluto covers pressure, what is hidden and what will not be treated casually.
A trine connects two functions without friction. Applied here, the standard reading is that intensity is available rather than intrusive: a person who can sit with heavy material, who reads a room accurately, and who is not particularly frightened by other people's crises. It is often described as resilience, which is fair as long as it is not read as immunity.
The honest caveat about trines is that nothing forces you to use one. A square nags. A trine simply sits there, and the capacity it describes can go unnoticed for decades because it never presents itself as a problem to solve. That is the standard criticism of the aspect and it is a reasonable one.
Orb, house and the rest of the chart
Pluto stays in a sign for between twelve and thirty years, so the sign here is shared with an enormous number of people. The houses are what individualise it, and they need a birth time. A trine from the fourth to the eighth reads through family and inherited material. From the third to the eleventh it reads through the way a person talks and who they talk to.
Orb decides strength. Inside two degrees the trine tends to be recognisable. Beyond five it is faint, and a tight square from anything else to the Moon will usually be the louder feature.
Pluto is retrograde for close to half of each year, so a natal retrograde Pluto in this aspect is the common case, not a variant that needs its own paragraph.
What it does not tell you
A trine is not a guarantee and it is not a personality. It describes a route between two parts of a chart that has no obstacle in it, and whether anything travels along that route depends on the whole chart and on a life the chart cannot see.
Nor does it say anything about events. Aspects between a fast body and a slow one describe how a chart is wired, not what happens to the person carrying it, and the gap between those two claims is where most bad astrology lives.
It is also worth saying that an isolated Moon and Pluto trine, wide and unaspected by anything else, is minor. A page that turns that into a portrait is filling space.
The check above gives the orb, both houses, both signs and whether the aspect crosses an element boundary, which is where the general description stops and your chart starts.
Questions people ask about this
How many degrees apart is a trine?
A hundred and twenty degrees, a third of the circle. We treat it as active within seven degrees, so anywhere from about a hundred and thirteen to a hundred and twenty seven degrees counts.
Is Moon trine Pluto a lucky aspect?
The tradition calls trines easy rather than lucky, and it makes no claim about outcomes. What it describes is a connection with no friction in it, which can as easily be left unused as put to work.
How long does the Moon stay in trine to Pluto?
About a day per window, twice a month, because the Moon covers thirteen degrees a day and the seven degree orb gives a fourteen degree band on each side. A tight orb inside one degree lasts roughly two hours.
Do both bodies have to be in the same element?
Usually but not always. A trine near the edge of the orb can span two signs of different elements, and that version generally reads more weakly than one where the elements match.
Is this a generational aspect?
No. Pluto by sign is generational, but the Moon moves fast enough that the trine belongs to particular hours of a particular day rather than to everyone born in a period.
What makes the aspect stronger?
A tight orb, an angular house, and a third body completing a pattern such as a grand trine. Without any of those, a wide trine to Pluto is a background feature of the chart.