Mercury in a chart covers thinking, speech, learning and the way information gets processed. But before the meanings, one astronomical fact is worth understanding, because nearly everything else follows from it: Mercury is tied to the Sun and cannot get away.
A maximum distance of 27.79 degrees
We computed daily positions of the Sun and Mercury across 90 years, from 1936 to 2025, which is 32,873 points. The greatest separation over that whole span was 27.79 degrees, on 31 March 1967. The average separation is 14.66 degrees.
For comparison, Venus reached 47.19 degrees over the same period. Mercury stays almost twice as close to the Sun, because its orbit is smaller.
The consequence is simple and checkable: Mercury can only be in the Sun's sign, the one before it, or the one after. There is no fourth option. If a site shows you the Sun in Aries and Mercury in Leo, the date or the time zone is wrong.
How the three options divide up
- Mercury in the Sun's sign: 51.1%
- In the previous sign: 24.4%
- In the next sign: 24.4%
So slightly more than half of people have Mercury where the Sun is, and for them the solar description matches the way they think. For the other half the thinking runs in a different sign from the character, and that is where the feeling of "I am nothing like my sign" often comes from.
Mercury retrograde at birth
By the same calculation Mercury is retrograde on 19.2% of days. Roughly one person in five is born with Mercury retrograde, which makes it not a rarity but the normal condition for a fifth of everyone.
In practice it means a different order of processing, not a worse quality of it. Such people come back to what was said, rephrase and check, and their outward reaction speed is lower. They often handle transiting retrogrades more easily than everyone else, because that is their default mode.
A separate figure: Mercury retrograde and in the Sun's sign at once occurs in 12.8% of charts.
Cazimi: the rare conjunction
In traditional astrology a planet is cazimi when it sits closer than 17 arcminutes to the Sun. That is not combustion but its opposite, a strengthening.
- Cazimi, within 17 minutes: 0.80% of days
- Within 1 degree: 2.87%
- Within 3 degrees: 8.61%
- Within 8 degrees (the traditional combustion limit): 23.45%
Mercury cazimi turns up in roughly one person in a hundred and twenty-five. Combust, meaning closer than 8 degrees but outside cazimi, in nearly one in four.
Morning star and evening star
Mercury ahead of the Sun in longitude is called the evening star, behind it the morning star. Tradition assigns them different mental tempos: the morning Mercury formulates faster, the evening one deliberates longer.
The split turned out even to within a tenth: 50.1% ahead, 49.9% behind. Neither is rare, so building a claim of distinctiveness on it does not hold up.
What to look at in the chart
- Mercury's sign. The way of thinking and phrasing. Do not confuse it with the Sun sign: for half of people they differ.
- The house. The area where a person talks, learns and exchanges information most.
- The distance from the Sun. Under 3 degrees means thinking is fused with the personality: such a person rarely looks at their own thoughts from outside.
- Retrograde motion. An internal processing order instead of an external one.
- Aspects. Saturn slows and sharpens, Uranus accelerates and interrupts, Neptune blurs the wording.
The exact degrees of Mercury and the Sun come from a natal chart for your birth date. The birth time matters less here than it does for houses: Mercury moves up to two degrees a day, so the sign is almost always unambiguous even without the exact hour.
In short
Mercury does not stray further than 27.79 degrees from the Sun across 90 years of measurement, so it sits in one of three signs only: the Sun's (51.1%), the previous one (24.4%) or the next one (24.4%). It is retrograde at birth for 19.2% of people and cazimi for 0.8%.
Try calculating your chart for free on AstroWay and see how far your Mercury has moved from the Sun.