October 9 is a shared birthday in the Lennon family. John Lennon was born on 9 October 1940 in Liverpool. His son Sean Lennon was born in Manhattan on October 9, 1975, which Sean's Wikipedia article notes was "his father's 35th birthday" (Sean Lennon, John Lennon).
People born on the same date are often called birthday twins. Astrologically, that's a much smaller overlap than it sounds. A birthday twin is not a chart twin. Here's what these two charts actually share, and where they part ways.
How the comparison was made
Both charts are date-only. John's profile has no birth time. Sean's stores one, but this comparison deliberately doesn't use it, so the two charts are treated the same way.
Each full local birthday was sampled every hour plus 23:59 with Lunara's central Swiss Ephemeris engine, in its own time zone: British time in 1940 Liverpool, Eastern time in 1975 New York. Only placements that hold across the whole day are compared. These are sampled ranges, not a continuous proof. There are no houses and no Rising sign, and no Moon is assigned from noon.
For closeness between the two charts, this article uses an 8° orb for conjunctions.
What a shared birthday gives you: the Sun
The Sun moves about one degree a day and returns to roughly the same place each year on the same date. So same-date birthdays nearly always share a Sun position.
- John: Sun at about 15½–16½° Libra
- Sean: Sun at about 15¼–16¼° Libra
Across the two days the Suns are within about 1¼° of each other. That's the part of the chart a birthday guarantees, and it's real.
A coincidence worth noticing: Venus
Venus doesn't follow the calendar the way the Sun does. On these two birthdays, though, it happens to land in nearly the same spot.
- John: Venus at about 2–3½° Virgo
- Sean: Venus at about 3–3½° Virgo
That's within about 1° all day for both. It's a genuine overlap, but it comes from Venus's own cycle, not from the shared date. Many people born on October 9 in other years won't have it.
Where the charts part ways
The planets that move fast or irregularly tell a different story:
- Moon: John's Moon left Capricorn for Aquarius at about 11:43 local time, so without a birth time it's Capricorn or Aquarius. Sean's Moon stays in Sagittarius all day, roughly 10–24°. Either way, different signs.
- Mercury: John's is in Scorpio, about 7½–9°. Sean's is in Libra, about 15–16°, and retrograde. They're more than 20° apart, in different signs.
- Mars: John's is at the start of Libra, about 2–3°. Sean's is at the end of Gemini, about 27½–28°.
Against the 8° conjunction orb, only the Sun pair and the Venus pair qualify. The two Mars positions are about 94–95° apart, and the two Mercury positions about 22–24° apart, so neither pair is a conjunction.
The slow outer planets differ completely too. Thirty-five years moves Jupiter through the zodiac roughly three times, and Saturn, Uranus, Neptune and Pluto into entirely different signs.
What that means symbolically
In astrology, the Sun is read as core identity and Venus as taste and what's valued. On those two points, the charts speak a similar language: a Libra Sun's attention to balance and proportion, and a Virgo Venus's eye for craft and detail.
The Moon (emotional needs), Mercury (thinking and voice) and Mars (drive) are where astrologers would expect two people to differ most. In these two charts, they do. The open Moon is worth a moment. A Capricorn Moon is read as steadiness and self-reliance, an Aquarius Moon as some distance and independence, and a Sagittarius Moon as a need for room and meaning. John's chart stays open between the first two; Sean's sits firmly in the third. Even with a matching Sun and a matching Venus, the overall pattern is not the same chart, and it isn't inherited.
None of this explains either person's public work. John Lennon is a founder of the Beatles and Sean Lennon is a musician, per their Wikipedia articles. The charts are a symbolic lens, not a family resemblance in disguise.
Check your own birthday twins
If you share a birthday with someone in your family, the comparison works the same way. Compare the Sun first, which will almost always match, and then look at the Moon, Mercury, Venus and Mars, which usually won't. The free natal chart calculator gives you all of these, and tells you if your Moon sign changes on your birth date.
Both profiles are here, each with its own clock notes: John Lennon's natal chart and Sean Lennon's natal chart.
Text written with AI assistance. The positions are calculated, not estimated.