Sixty degrees and a narrow window
A sextile is sixty degrees with an orb of about five, the tightest allowance of the five major aspects. The Moon passes through both sextiles to the Sun each lunar month, one waxing at the crescent stage and one waning, but the narrow orb means each window is open for well under a day.
That makes this less common at birth than the square or the trine even though the Moon makes the same number of passes. Orb, not geometry, is doing the filtering. It is also why a sextile is easier to miss when scanning a chart quickly.
The waxing sextile puts the Moon in the crescent that you see in the west just after sunset. The waning one is the crescent visible before dawn. Both are recognisable in the sky, which is more than can be said for the trine.
An offer rather than a fact
The Sun is intention, the Moon is the default setting underneath it. Where a trine says the default already serves the intention, a sextile says it can if you route it that way. The signs involved are two apart and share a polarity but not an element, fire with air or earth with water, so they are compatible without being the same.
The practical description is a workable relationship between what you want and what you are comfortable doing, provided you notice it. Nothing here is forced. There is no friction to make you act and no automatic support to carry you, which is why the sextile is the aspect most often read as latent.
People with this contact frequently report that they can settle themselves down when they choose to, and that they do not always choose to. That is a fair paraphrase of what the tradition claims for the aspect, and it is deliberately modest.
What the pairing of elements does
Fire and air sextiles between the lights read as an easy match between drive and articulation. What you want you can usually say, and saying it tends to help. Earth and water sextiles read as an easy match between practicality and instinct, where a feeling about a situation and a sensible response to it arrive together.
House placement narrows it further. A sextile from a fifth house Sun to a third house Moon is a different resource from one between a tenth house Sun and an eighth house Moon. The general reading is thin enough that the specifics carry most of the weight, which is not true of the harder aspects.
Orb, and knowing when to drop it
Five degrees is the standard maximum here and many astrologers work tighter, at three or four, precisely because a wide sextile does almost nothing. If yours is at four and a half degrees, it is reasonable to note it and move on to the aspects that are actually shaping the chart.
The Moon's speed makes birth time matter. Thirteen degrees a day means an hour of error moves the Moon by roughly half a degree, so a sextile reported at four point eight degrees on an uncertain birth time might be no sextile at all. Where the time is rounded to the nearest hour, treat the reported orb as approximate.
The check above gives the exact separation as calculated, along with both signs and houses. If the figure comes back tight, this is worth reading properly. If it comes back near the limit, the honest answer is that it is a minor feature.
Questions people ask about this
What is the orb for Sun sextile Moon?
About five degrees, and many astrologers use less. It is the narrowest allowance of the five major aspects, which is why sextiles are less commonly found in charts than squares or trines despite occurring just as often in the sky.
Is a sextile weaker than a trine?
In the usual ranking, yes. Both are read as easy contacts, but the trine is treated as automatic and the sextile as available on request. The narrower orb reinforces that, since a sextile has less room to be tight.
Which moon phase gives a sextile?
The crescent stages, waxing or waning, when the Moon is sixty degrees from the Sun. That is the thin crescent low in the west after sunset, or the matching one in the east before dawn.
What elements do the signs share?
None, but they share a polarity. Sextiles pair fire with air or earth with water, so the two bodies are compatible without being alike. That mixture is what the tradition reads as cooperation rather than agreement.
Does an imprecise birth time affect this?
More than for slower pairs. The Moon covers about thirteen degrees a day, so an hour of uncertainty is roughly half a degree of orb. Near the five degree limit that can decide whether the aspect is counted at all.
Should I read anything into a five degree sextile?
Very little on its own. At the edge of orb the aspect is a background note. It becomes worth attention when the orb is tight, or when the same two bodies are also involved in stronger configurations elsewhere in the chart.