Sun-Sun Synastry: Two Suns Measured by Degree, Not Only by Sign

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A Sun-Sun contact is a major aspect between the Sun in one person's birth chart and the Sun in the other person's. Astrologers read the Sun as identity, purpose and the kind of life a person is trying to build, so comparing two Suns is usually read as a question of recognition: whether each person's sense of direction is familiar to the other, complements it or pulls against it. That is a theme to test against how the two people actually get on. It is not a measure of ego, a ranking of who leads, or a forecast that two people will compete.

Educational guide: Astrologist.com does not currently calculate synastry, inter-chart aspects, house overlays or composite charts. The compatibility tool provides a sign-level estimate based on the Sun, Moon and Rising signs; known birth times are required for that tool. The contacts discussed here must be identified separately from the two charts' actual positions.

Signs compared, or longitudes measured?

Most "Sun sign compatibility" reading compares two signs. The zodiac sign compatibility guides and pages such as Leo and Virgo compatibility describe how the qualities of two signs tend to combine. That is a sign-pair reading, and it is the layer the compatibility tool estimates.

Sun-Sun synastry asks something narrower: how many degrees separate the two Suns, and does that separation fall within orb of a conjunction, sextile, square, trine or opposition? The two layers often agree, because signs are measured in the same zodiac. They come apart near sign boundaries.

Here is an illustration with hypothetical positions, invented for this explanation and not taken from the calculator:

• A Sun at 2° Leo and a Sun at 28° Leo share a sign, but they are 26° apart. Under the 8° orb used on this site that is not a conjunction, and 26° is not within orb of any other major aspect either. A sign-pair reading would call these two "same sign"; a degree reading finds no Sun-Sun contact at all.
• A Sun at 27° Cancer and a Sun at 3° Leo sit in different signs, yet they are only 6° apart, which counts as a conjunction.

So a shared Sun sign does not establish a conjunction, and neither does a shared element for a trine. Only the measured separation does.

One separation, not two

A pair of charts has exactly one Sun-Sun separation. Measuring from A's Sun to B's or from B's Sun to A's gives the same number, so swapping the labels does not produce a second contact and does not give either person a different role. Mixed pairs such as Sun-Mars work differently, because there each direction uses different planets.

There is also no natal version of this page. One chart has one Sun, so "Sun conjunct Sun" or "Sun square Sun" cannot occur within a single birth chart. Every Sun-Sun aspect is an inter-chart measurement, and all five major aspects are possible between two charts.

What the five aspects are read as

These are common interpretive themes, offered as possibilities rather than findings:

• Conjunction. Two people whose sense of purpose points the same way. Astrologers often describe quick recognition, sometimes a feeling of being understood without explanation. The same closeness can mean both want the same kind of role, which is something to talk about, not a guarantee of rivalry.
• Sextile. Directions that differ but support each other. Each may find the other's aims easy to encourage.
• Square. Two sets of priorities that ask for different things at the same time. Read as friction to name and negotiate, not as incompatibility or a verdict on either person.
• Trine. Aims that tend to fit without much adjustment. If that ease is present, it can leave differences unexamined.
• Opposition. Each person's direction may stand for what the other has not chosen. That can widen both people's view or turn into a habit of taking opposite sides.

None of these says who is the stronger personality, who should lead, or whether a relationship will last.

Worked example: birthdays eight days apart

Two fictional people, with positions from the Astrologist.com natal calculator:

• Person A: 19 August 1979, 21:30, Bristol. British Summer Time (UT+1) applied, so the birth was at 20:30 UT. Sun 26°15' Leo.
• Person B: 27 August 1984, 04:10, Antwerp. Central European Summer Time (UT+2) applied, so the birth was at 02:10 UT on the same date. Sun 3°59' Virgo.

In zodiac longitude, 26°15' Leo is 146°15' and 3°59' Virgo is 153°59'. The difference is 153°59' minus 146°15', which is 7°44'. That is a conjunction 7°44' from exact, only 0°16' inside the 8° limit. The calculator's own longitudes, 146.26 and 153.99, give 7.73.

By sign, this is a Leo Sun and a Virgo Sun, a neighbouring-sign pairing. By degree, it is a conjunction. An astrologer might read both layers: Leo's wish to be seen and Virgo's wish to be useful, joined by a contact that suggests each recognises how the other is trying to make a mark.

Why the birthdays alone do not decide it

The Sun moves about one degree a day, so it is tempting to assume that birthdays about a week apart give a conjunction. This pair shows why that has to be checked. Each local birth date was recalculated at every whole minute from 00:00 to 23:59, using the time zone and summer time in force:

• Bristol, 19 August 1979 ran from 23:00 UT on 18 August to 22:59 UT on 19 August. A's Sun moved from 25°24' to 26°21' Leo.
• Antwerp, 27 August 1984 ran from 22:00 UT on 26 August to 21:59 UT on 27 August. B's Sun moved from 3°49' to 4°47' Virgo.

Neither Sun changed sign or direction during its date, so the extremes fall at the start and end of each day.

• If only A's time were unknown, the separation from B's known Sun ran from 8°35' at 00:00 down to 7°38' at 23:59. The calculator puts it at the 8.00 edge from 14:43 local time (13:43 UT). Before about 14:30 there is no conjunction, after about 15:00 there is, and in between the result sits inside the calculator's 0.01° rounding, since the Sun takes about 14 minutes to move 0.01°.
• If only B's time were unknown, the separation from A's known Sun ran from 7°34' at 00:00 to 8°32' at 23:59. It is in orb until 10:56 local time and outside from 10:57 (08:57 UT), with roughly 10:45 to 11:10 undecidable at that precision.
• With both times unknown, the 2,073,600 pairings of the two dates gave separations between 7°28' and 9°23'. Some pairings form a conjunction and others form nothing, so the contact holds only for part of the possible times. A share of those pairings would describe the grid, not a chance of the contact being real, so it is not quoted here.

The calendar adds its own drift. At noon in Bristol the calculator puts the Sun at 25°52' Leo on 19 August 1979 but at 26°36' Leo on 19 August 1980, because the leap-year cycle shifts where a given date falls. The same pair of birthdays can therefore give a different separation in different years. A close birthday is a reason to measure, not a result. Step-by-step measuring is covered in comparing two charts by degree, and boundary cases like this one in out-of-sign aspects.

Questions to talk through

• What is each of you trying to build at the moment, and where do those aims overlap?
• When you feel recognised by the other person, what are they actually noticing?
• Is there a role you both reach for, at home or at work, and how do you share it now?
• What does each of you want the other to take seriously about your plans?

The orb convention

This guide counts a conjunction, square, trine or opposition within 8° of exact and a sextile within 6°, with a value exactly on the limit counted as in orb. The natal calculator uses those orbs within one chart; here they serve only as a consistent convention for examples, and nothing on the site measures Sun-Sun contacts between two people. Many astrologers give the Sun a wider orb in synastry, which would change borderline pairs like the one above. This guide does not, and it draws no line between applying and separating aspects.

Next steps

Make a free birth chart for each person, one at a time, and read the Sun's degree and sign from each planet table. Convert both to longitude and take the shorter way round.

If a birth time is missing, keep in mind what the ordinary chart shows. The free chart still calculates from the birth date, but its planet table then uses local noon as a date reference, not the person's actual birth time, and it does not show the range the Sun covered over that day. To see that range, keep the same birth date and place, so the chart applies the same historical local clock rules, and enter hypothetical test times at the start and end of the local date. The Sun always moves forward, so those two ends give its full range for the day. Use those test charts only to read the Sun's position, and ignore the Ascendant, houses and other angles they produce, because they belong to the test time, not to the person. If both birth times are unknown, vary each person's test time independently, then compare the smallest and largest possible separation with the orb.

For the Sun against the other person's Moon, see Sun-Moon synastry. Two other same-planet comparisons are Mars-Mars synastry and Jupiter-Jupiter synastry.

Related articles

• Synastry Basics
• Sun-Moon Contacts in Synastry
• Sun-Mercury Synastry
• Moon-Moon Contacts in Synastry
• Zodiac Sign Compatibility
• Jupiter-Jupiter Synastry
• All compatibility guides