The angle, the orb and how often it happens
A conjunction is two bodies at the same ecliptic longitude, and for a pair like this the working orb is eight degrees. The Moon covers about thirteen degrees a day, Jupiter about a twelfth of a degree, so the two close and separate at roughly the Moon's own speed.
That gives a window of a little over a day either side of the exact meeting, once every twenty seven or so days as the Moon laps Jupiter. Across a whole population it is not rare. What is unusual is a tight version: getting inside one degree takes a couple of hours, and those hours are fixed by where on Earth you were born as much as by the date.
Jupiter spends about a year in each sign, so the sign of the conjunction is shared by everyone born that year. The degree, the house and the exact orb are yours.
Worth separating two things that often get muddled. Jupiter's sign is a fact about the year you were born in, and it is shared by roughly a twelfth of everyone alive. The conjunction is a fact about the day, and a tight conjunction is a fact about the hour. Only the last of those describes a person.
What the tradition reads into the pair
The Moon in traditional practice is instinct, appetite, the reflex response before thought arrives. Jupiter is the principle of increase: whatever it touches gets more room, more confidence and less editing.
A conjunction fuses rather than balances, so the reading is an appetite with the brakes loosened. Older sources call it generous and describe a person whose first reaction to almost anything is to say yes and worry later. The same mechanism read less kindly is a reflex that overcommits, promises more than the week can hold, and treats a mood as a plan.
Neither description is a verdict. Jupiter enlarges the Moon it finds, so a cautious Moon in Virgo enlarged is still a Virgo Moon, just with a wider margin. The sign does more work here than the aspect does.
Why the birth time decides this one
Most contacts to Jupiter are shared by everyone born inside a stretch of weeks. This one is not, and that is worth stating plainly, because it is the difference between a personal placement and a background note.
An unknown or rounded birth time is the main risk. A chart cast for noon when the birth was at six in the morning moves the Moon by about three and a half degrees, which can turn a two degree conjunction into a six degree one, or the reverse. If you are working from an approximate time, treat the orb the widget above reports as approximate too.
Jupiter retrograde does not change the picture much here. It is retrograde for about four months a year, which only slows the closing slightly.
Orb, sign and house
Inside two degrees the description above tends to be recognisable to the person concerned. Between four and eight it is one note among many, and it is easily outweighed by a hard aspect from Saturn to the same Moon.
House placement is what makes two people with the identical conjunction live differently. In the second house the appetite attaches to money and comfort, in the ninth to travel and belief, in the fourth to home and family size. The sign sets the flavour and the house sets the subject.
The check above gives you the orb to the minute, the sign and, if you have a birth time, the house. That is the part a general description cannot supply.
Look also at whether the pair sits near an angle. A conjunction within a few degrees of the ascendant or midheaven is read as considerably more prominent than the same conjunction buried in the eighth house, and that difference is entirely a matter of the birth time.
Questions people ask about this
How often does Moon conjunct Jupiter occur?
The Moon passes Jupiter roughly once every twenty seven days, and the eight degree orb holds for a little over a day either side. So it happens monthly, but a tight orb of a degree or less lasts only about two hours.
Is Moon conjunct Jupiter a lucky aspect?
The tradition associates Jupiter with increase rather than with luck, and a conjunction enlarges whatever Moon it finds. Whether that reads as fortunate depends on the sign, the house and what else aspects the pair.
Does the birth time matter for this aspect?
More than for almost any Jupiter contact. The Moon moves about half a degree an hour, so a few hours of error can change the orb by several degrees or remove the aspect altogether.
What does Jupiter retrograde do to it?
Very little. Jupiter is retrograde for about four months of every year, so a natal retrograde Jupiter is ordinary. The Moon supplies nearly all of the relative motion in this pair either way.
Does everyone born that year have it?
No. Everyone born that year shares Jupiter's sign, but only those born during the monthly window when the Moon caught up have the conjunction, and only a small fraction have it tightly.
Which aspect is usually contrasted with it?
Moon opposite Jupiter, where the same two bodies sit across the chart from each other rather than merged. That version puts the appetite in dialogue with something instead of letting it run unchecked.