Two Calendars, One Sky
In Japan, the year doesn’t have just four seasons. It has twenty-four.
They are called the 24 solar terms, or nijūshi sekki (二十四節気). For more than two thousand years, they have told farmers when to plant, poets what to write about, and families when to change their wardrobes.
Here is the surprise: these 24 seasons are measured with the exact same ruler Western astrologers use for the zodiac. Both systems track one thing — the Sun’s journey through the sky. Once you see the connection, you’ll never look at your Sun sign, or the calendar, the same way again.
What Are the 24 Solar Terms?
The 24 solar terms are a seasonal calendar that splits the year into 24 periods of roughly 15 days each. Each term has a poetic name that describes what is happening in nature — Grain Rain, Insects Awaken, Cold Dew, Frost Descends.
Where they come from
The system was developed in ancient China, around the Yellow River basin, to guide agriculture. A complete list of all 24 terms already appears in the Huainanzi, a text from the 2nd century BCE. The calendar later traveled to Japan, where it blended into daily life and seasonal culture. In 2016, UNESCO added the 24 solar terms to its list of Intangible Cultural Heritage.
How they are calculated
This is the key detail. The solar terms are not based on the Moon. They are based on the Sun’s position along the ecliptic — the apparent path the Sun traces across the sky over one year.
The ecliptic is a 360° circle. Divide it into 24 equal slices, and each slice is 15°. Every time the Sun crosses one of those 15° marks, a new solar term begins. Japan has used this precise, Sun-position method (teiki-hō, 定気法) since the Tenpō calendar reform of 1844.
Why they still matter in Japan
You’ll still hear the solar terms on Japanese weather forecasts and see them on calendars. Haiku poets use them as seasonal words. Shops change displays for Risshun (the start of spring) and families eat pumpkin on Tōji (the winter solstice). They are a living way of tuning into the season.
The Surprising Common Ground: The Same 360° Circle
Western astrology’s zodiac is also the ecliptic, divided into 12 signs of 30° each. Your Sun sign is simply the 30° slice the Sun was passing through on the day you were born.
So the two systems measure the same circle:
- Zodiac: 360° ÷ 12 signs = 30° per sign
- Solar terms: 360° ÷ 24 terms = 15° per term
That means every zodiac sign contains exactly two solar terms. One begins at 0° of the sign, the moment the Sun enters it. The other begins at 15°, the exact midpoint of the sign.
In the traditional East Asian calendar, these two types even have names. The term at 0° of a sign is a chūki (中気, “principal term”). The term at 15° is a sekki (節気, “sectional term”). In other words, an ancient Chinese calendar quietly marked every zodiac sign ingress for two thousand years.
There’s one more twist. The old lunisolar calendar named its months by which chūki fell inside them. A lunar month with no chūki became the leap month. Put in astrology terms, a month in which the Sun changed signs was a normal month — and a month in which it didn’t was the extra one.
The Complete Map: 24 Solar Terms and the 12 Zodiac Signs
The table starts at the spring equinox, 0° Aries, where the Western zodiac begins. Dates shift by a day or so from year to year.
| Solar term | Meaning | Approx. date | Sun’s longitude | Zodiac position |
|---|---|---|---|---|
| Shunbun (春分) | Spring Equinox | Mar 20–21 | 0° | Sun enters Aries |
| Seimei (清明) | Clear and Bright | Apr 4–5 | 15° | Mid-Aries |
| Kokuu (穀雨) | Grain Rain | Apr 19–20 | 30° | Sun enters Taurus |
| Rikka (立夏) | Start of Summer | May 5–6 | 45° | Mid-Taurus |
| Shōman (小満) | Lesser Fullness | May 20–21 | 60° | Sun enters Gemini |
| Bōshu (芒種) | Grain in Ear | Jun 5–6 | 75° | Mid-Gemini |
| Geshi (夏至) | Summer Solstice | Jun 21 | 90° | Sun enters Cancer |
| Shōsho (小暑) | Minor Heat | Jul 7 | 105° | Mid-Cancer |
| Taisho (大暑) | Major Heat | Jul 22–23 | 120° | Sun enters Leo |
| Risshū (立秋) | Start of Autumn | Aug 7–8 | 135° | Mid-Leo |
| Shosho (処暑) | End of Heat | Aug 23 | 150° | Sun enters Virgo |
| Hakuro (白露) | White Dew | Sep 7–8 | 165° | Mid-Virgo |
| Shūbun (秋分) | Autumn Equinox | Sep 22–23 | 180° | Sun enters Libra |
| Kanro (寒露) | Cold Dew | Oct 8 | 195° | Mid-Libra |
| Sōkō (霜降) | Frost Descends | Oct 23 | 210° | Sun enters Scorpio |
| Rittō (立冬) | Start of Winter | Nov 7 | 225° | Mid-Scorpio |
| Shōsetsu (小雪) | Lesser Snow | Nov 22 | 240° | Sun enters Sagittarius |
| Taisetsu (大雪) | Greater Snow | Dec 7 | 255° | Mid-Sagittarius |
| Tōji (冬至) | Winter Solstice | Dec 21–22 | 270° | Sun enters Capricorn |
| Shōkan (小寒) | Lesser Cold | Jan 5–6 | 285° | Mid-Capricorn |
| Daikan (大寒) | Greater Cold | Jan 20 | 300° | Sun enters Aquarius |
| Risshun (立春) | Start of Spring | Feb 3–4 | 315° | Mid-Aquarius |
| Usui (雨水) | Rain Water | Feb 18–19 | 330° | Sun enters Pisces |
| Keichitsu (啓蟄) | Insects Awaken | Mar 5–6 | 345° | Mid-Pisces |
Tip: when you see a horoscope headline like “the Sun enters Taurus,” you can say “Grain Rain begins” — and be equally correct.
Three Overlaps Every Astrology Lover Should Know
1. Equinoxes and solstices = the cardinal signs
The four great turning points of the solar year sit at 0° of the four cardinal signs — Aries, Cancer, Libra and Capricorn. In the solar terms, they are Shunbun, Geshi, Shūbun and Tōji. Both traditions treat these as the year’s most powerful moments.
2. “Start of the season” = the heart of the fixed signs
Risshun, Rikka, Risshū and Rittō — the four “starts” of spring, summer, autumn and winter — arrive when the Sun reaches 15° of Aquarius, Taurus, Leo and Scorpio: the exact middle of the four fixed signs. These points fall roughly midway between the solstices and equinoxes — the same part of the year as the Celtic seasonal festivals of Imbolc, Beltane, Lughnasadh and Samhain, which are traditionally celebrated on fixed calendar dates a few days earlier. It’s a striking echo: cultures far apart both marked this midpoint of each season.
3. East and West start the seasons at different times
Here the two systems disagree in a beautiful way. Western astrology says spring begins when the Sun enters Aries. The solar terms say spring begins at Risshun, about 45 days earlier, in mid-Aquarius.
In the Eastern view, the equinoxes and solstices are the peak of each season, not the start. Western astrology reads the season by its active, cardinal launch. The solar terms read it by the first quiet signs of change in nature. Holding both views gives you a richer sense of timing.
Season by Season: Where Nature and the Zodiac Agree
The poetic names of the solar terms often echo the personality of the sign the Sun is passing through.
Spring: Aries, Taurus, Gemini
Seimei (Clear and Bright) arrives in mid-Aries, matching the sign’s fresh, fearless energy. Kokuu (Grain Rain) opens Taurus with nourishing rain for crops — fitting for the earthy sign of abundance. Shōman (Lesser Fullness) begins Gemini as plants grow fast and the world feels busy.
Summer: Cancer, Leo, Virgo
Geshi, the longest day, opens Cancer, the sign of home and nurture. Taisho (Major Heat) begins Leo — the Sun’s own sign arrives with the hottest days of the year. Shosho (End of Heat) opens Virgo, when the air cools and it’s time to sort, tidy and prepare.
Autumn: Libra, Scorpio, Sagittarius
Shūbun balances day and night as the Sun enters Libra, the sign of the scales. Sōkō (Frost Descends) opens Scorpio as the year turns toward endings and depth. Shōsetsu (Lesser Snow) begins Sagittarius, a time to look ahead to the long journey of winter.
Winter: Capricorn, Aquarius, Pisces
Tōji, the darkest day, opens Capricorn — the sign of patient, steady building. Daikan (Greater Cold) begins Aquarius, yet Risshun, the first breath of spring, arrives in the middle of that same sign. Usui (Rain Water) opens Pisces as snow melts into water, perfect for the sign of flowing emotion.
How to Use the Solar Terms in Your Astrology Practice
- Check in twice a month. Treat each sign ingress (0°) as a time to set an intention, and each mid-sign term (15°) as a check-in on how that intention is growing.
- Mark the fixed-sign midpoints. Risshun, Rikka, Risshū and Rittō are ideal moments for seasonal resets — decluttering, journaling or starting a new routine.
- Find your birth term. Look up which solar term was active on your birthday. A Taurus born in early May shares their birth window with Rikka, the start of summer, while a late-April Taurus was born under Kokuu. It adds a seasonal layer to your Sun sign.
- Let nature be your cue. The term names describe real weather and growth. When Hakuro (White Dew) brings dew to the grass in mid-Virgo, notice it. Grounding your astrology in the physical season makes it feel more alive.
- Eat with the season. Japanese tradition pairs many terms with seasonal foods — such as pumpkin and a yuzu bath on Tōji. Small rituals help you feel each Sun shift in your body.
Right Now: Cold Dew and Frost Descends
In October, we are moving through two terms that capture autumn’s turn inward.
- Kanro (寒露, Cold Dew) — around October 8, mid-Libra. Morning dew turns chilly. Libra season reaches its midpoint, a good moment to review your relationships and restore balance before the deeper months.
- Sōkō (霜降, Frost Descends) — around October 23, Sun enters Scorpio. The first frost appears in Japan’s mountains and the leaves begin to turn. Scorpio’s intensity arrives with nature’s quiet letting-go — a perfect time for release and transformation.
Two weeks later, around November 7, Rittō marks the start of winter at mid-Scorpio — the same point as Samhain.
FAQ
Are the 24 solar terms based on the Moon?
No. Even though they came from a lunisolar calendar, the solar terms follow only the Sun’s position. That’s why their dates barely change on the Western calendar.
Why do solar term dates change by a day each year?
The Sun crosses each 15° mark at a slightly different time each year, because a calendar year doesn’t match the solar year exactly. Leap years also shift dates. The same is true for the exact day the Sun changes zodiac signs.
Is the zodiac used here the same one in my horoscope?
Yes. Most Western astrologers use the tropical zodiac, which starts at the spring equinox. The solar terms are measured from the same starting point, so the two line up perfectly.
Are the 24 solar terms the same as Chinese astrology?
Not exactly. Chinese astrology’s animal signs follow a 12-year cycle. However, the solar terms do define the months in some Eastern systems — for example, Risshun is often used as the start of the year in Four Pillars of Destiny.
What are the 72 microseasons?
Each solar term is divided into three smaller periods of about five days, creating 72 kō (七十二候). Each has an even more detailed nature name, like “Swallows return.”
Conclusion: One Sun, Two Beautiful Languages
The 24 solar terms and the Western zodiac grew up worlds apart, yet they read the very same sky. Every zodiac sign holds two solar terms. The equinoxes and solstices anchor both systems. And the “start of the season” terms land exactly where Europe’s ancient festivals did — at the heart of the fixed signs.
Next time the Sun changes signs, look up its solar term too. You’ll find your horoscope has a second voice, one that speaks in dew, frost, rain and blossoms.
Want to follow the Sun’s journey all year? Subscribe to AstroVibes Journal for monthly horoscopes and seasonal astrology guides, and save this post to come back at every new solar term.
