The angle and how the orb works
A square is a quarter of the circle, ninety degrees, with a working orb of seven. The Moon makes two squares to Jupiter in each circuit of the zodiac, one waxing and one waning, so this shows up about twice a month.
At thirteen degrees a day the Moon crosses the fourteen degree band in a little over twenty four hours. A square inside one degree occupies under two hours of that. So while the aspect itself is common, the tight version depends on a recorded birth time in a way that Jupiter's sign never does.
Squares fall between signs of the same mode, cardinal with cardinal, fixed with fixed, mutable with mutable. That shared mode tells you how the friction behaves: cardinal starts things, fixed digs in, mutable keeps changing tack.
Appetite meeting a limit
The Moon is the reflex, the need that arrives before you have thought about it. Jupiter enlarges what it touches and rarely suggests that anything is sufficient.
At ninety degrees the two do not merge and cannot simply look at each other across the chart. They interrupt each other. The classic reading is overindulgence followed by a reckoning, promises made in a good mood and honoured with difficulty, an emotional scale set slightly too large for the circumstances. Read more usefully, it is a person who keeps discovering their own limits by walking into them, and who therefore learns where they actually are.
Older texts call this aspect immoderate. That is a description of a mechanism and not a character verdict, and the sign does at least as much work as the angle.
The waxing and waning versions are sometimes distinguished. A square made while the Moon is separating from its conjunction with Jupiter is read as the appetite pushing outward, while the closing square is read as it running up against a result. Not every practitioner uses the distinction, but it is a real difference in the geometry.
What changes it
Saturn is the first thing to look for. A Saturn contact to either body supplies the restraint the square lacks, and a chart with both often reads as disciplined generosity rather than excess.
Mode matters next. A cardinal square acts fast and moves on. A fixed square holds the same appetite for years. A mutable one scatters it.
Houses give it a subject. Second against fifth is money against pleasure. Fourth against seventh is family against partnership. The same ninety degrees produces quite different lives depending on which pair of houses it crosses, which is why the reading needs a birth time rather than just a birth date.
Also worth checking is whether the Moon rules an angle. A Moon ruling the ascendant carries far more of the chart than a Moon tucked into a cadent house, and the same square then describes much more of the person.
Frequency, retrogrades and proportion
Jupiter circles the zodiac in about twelve years and spends around four months of each year retrograde, so a natal retrograde Jupiter here is entirely ordinary and not a hidden signature.
Because the Moon supplies nearly all of the relative motion, this is a personal aspect. Everyone born in the same fortnight shares Jupiter's degree, but only those born in the right day or so have the square.
Keep it in proportion. A seven degree square that touches nothing else is a minor note, while a one degree square to a Moon that also rules an angle is a defining feature. The widget above gives you the orb and the houses so you can tell which of those you have.
Questions people ask about this
Is Moon square Jupiter a bad aspect?
The tradition reads squares as friction rather than harm. This one describes an appetite that keeps meeting its limits, and whether that produces overreach or good judgement depends on the rest of the chart.
What orb is used for a square?
Seven degrees. Inside two degrees the aspect is prominent and usually recognisable. Between five and seven it is a background note that a tighter aspect elsewhere will easily outweigh.
How often does it happen?
Twice per lunar circuit, so about twice a month, each pass lasting a little over a day within orb. It is one of the more frequently occurring aspects in any population.
Does Saturn change the reading?
Often decisively. A Saturn aspect to the Moon or to Jupiter supplies the restraint this square lacks, and charts with both tend to read as measured rather than excessive.
Are the two signs always the same mode?
Yes for an exact square, since ninety degrees is three signs. A wide square that crosses a sign boundary breaks that rule and is generally read as weaker.
Which aspect is the natural comparison?
Moon trine Jupiter, where the same two bodies cooperate instead of interrupting each other. Comparing the two is the clearest way to see what the angle itself contributes.