Search Jewish Cosmology
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Main pages and glossary
- API documentation
- Jewish Calendar and Astronomy
- Animation library
- Hebrew Calendar
- Halachic Times
- Sun
- Moon
- Planets
- Seasons
- Eclipses
- About Jewish Cosmology
- Experimental Hebrew Calendar
- Calendar According to Sighting
- Calendar and Astronomy Glossary
- Molad
- Shkiyah
- Netz HaChamah
- Tekufah
- Shaot Zmaniyot
- Atmospheric refraction
- Solar declination
- World map
- Calendar statistics
- Celestial
- Three Stars
- Rambam’s Kiddush Hachodesh
- Daylight savings
- Cycles
- Historical dates
- Support Jewish Cosmology
- Hebrew calendar · month grid
- Hebrew calendar · month list
- Hebrew calendar · yearly view
Statistics and studies
- Deriving the leap-year structure
- Hebrew year spans · Rosh Hashanah shifts
- Year spans · all month counts together
- Rosh Hashanah shift · line graph
- Variation across the cycle · calculated evidence
- Rosh Hashanah shift · each starting year
- Rosh Hashanah · Hebrew, Gregorian and Julian drift
- Rosh Hashanah dates
- Pesach drift · tekufot and theoretical Pesach
- Hebrew birthdays on Shabbat · ages 13 and 83
- 19-year cycle
- Molad repetitions · mathematical and astronomical
- Monthly molads · clock comparison graph
- Astronomical · true molad repetitions
- Lunar invisibility · 0–0.9% illumination
- Mean and true molad · time windows
- Rav Adda and Shmuel
- True tekufot
- Tekufos and Pesach · comparison graph
- Tekufos and Pesach · counts and percentages
- Postponements · counting conventions
- Keviyos · Rosh Hashanah weekday and year length
- Mathematical · mean molad repetitions
- True molad to true molad · years 1–10,000
- Astronomical molad · axial tilt and orbital comparisons
- Birchas hachama · 28-year cycles
- Tein tal umatar · year-range comparison
- Tein tal umatar · three tekufa calculations
- Reading report · range and custom
- Holidays
- 19-year cycle lengths and keviyos
- Rosh Chodesh and month-start weekdays
- Solar transects · times, durations and directions · years 1–10,000
- Worldwide · sunrise and sunset durations · years 1–10,000
- Temple Mount · daylight hours · years 1–10,000
- Sunrise, sunset and twilight · location study
- Parshios and haftarahs
- Planetary hours · astronomical matches
- Precessional drift · years 1–10,000
- Calendar measures · summary
- Molados · average lunar month
- True molad and lunar visibility
- Sunrise, sunset and twilight
- True Tekufos · astronomical equinoxes and solstices
- Jewish year structure
- Leap-year studies
- The four dechiyos
- Rosh Hashanah weekdays
- Keviyos and calendar cycles
- Year spans
- Dates and drift
- Tekufos · Rav Adda, Shmuel
- Birchas hachama
- Tein tal umatar livvracha
- Birthdays
- Astronomical Calculations
- The Moon (Yarei’ach)
- The Sun (Shemesh)
- Planets (Nogah, Tzedek, etc.)
- Stars & Zodiac (Mazalos)
- The Jewish Calendar
- Fundamentals & The Lunar Month
- Year Structure & Intercalation
- Rules of the Fixed Calendar (Keviyos)
- Long-Term Cycles & Drift
- Solar Alignments in Halacha
- Shabbos Readings
- Practical Applications
- Calendar report · range and filters
- Astronomical report · calculations and filters
- Molad Zakein witnesses · visual comparison
- Mean molad and solar noon
- Rosh Chodesh weekday distribution
- Rosh Chodesh by keviyah
- Individual holidays and fasts
- Combined holiday and fast weekdays
- Readings in the inspected year · within the range
- Comparison · Shmuel, True and Rav Adda
- 28-year cycle comparisons
- Rav Adda · 28-year Saturn comparisons
- True tekufa · 28-year Saturn comparisons
- Calendar measures · summary and sources
- Mean lunar month and solar years
- Historical lunar months · comparison graph
- Mean lunar month · historical and NASA comparisons
- Selected year · calculated intervals and averages
- NASA · 2026 lunations and published mean
- Temple Mount · sunrise duration and sunset direction · years 1–10,000
- Molad Zakein · Rosh Hashanah comparison
- What is being counted?
- Rosh Hashanah differences · counts and percentages
- Birthday conventions · explanation
- Birthday on Shabbat · comparison graph
- Birthday on Shabbat · counts for every date
- · Age · Matching birth years
- Leap-year structure · offset graph
- Leap-year structure · full-cycle verification
- Leap-year structure · proportion graph
- Derivation · year-by-year steps
- Tekufah matches · same Jewish day
- Planetary hours · astronomical matches
- Precessional drift
- Earth’s obliquity · historical values
- Tishri conjunction · comparison graph
- Mean molad versus true conjunction · line graph
- Lunar windows · summary and percentages
- Lunar windows · durations and percentages
- Lunar windows · comparison over time
- Low-illumination window around true conjunction
- Counts and data · durations and percentages
- Molad time ranges · counts and percentages
- hours after true conjunction · selected windows
- Counts and percentages
- Individual conjunctions
- Before and after true molad · over time
- True lunations and annual means versus the traditional molad
- True obliquity · axial tilt at the sampled date
- Month length, obliquity and eccentricity · comparison
- The role of Earth’s axial tilt · measured correlations
- Solar, lunar and apparent sidereal clock readings
- Sidereal day length versus a 24-hour clock day
- Lunar apogee and perigee · Earth–Sun and Moon–Sun distances
- True lunations · Hebrew year
- Tekufot · dates and differences
- Rosh Hashanah weekdays
- Year lengths · all years
- Common year lengths
- Leap year lengths
- Cheshvan and Kislev
- Postponements applied
- Postponement combinations
- Leap and common years
- Rav Adda · Tekufas Nisan
- Birkas HaChama · occurrences
- Birkas HaChama · Hebrew dates
- Keviyos · all years
- Cycle position · 1
- Cycle position · 2
- Cycle position · 3
- Cycle position · 4
- Cycle position · 5
- Cycle position · 6
- Cycle position · 7
- Cycle position · 8
- Cycle position · 9
- Cycle position · 10
- Cycle position · 11
- Cycle position · 12
- Cycle position · 13
- Cycle position · 14
- Cycle position · 15
- Cycle position · 16
- Cycle position · 17
- Cycle position · 18
- Cycle position · 19
- Monthly molads · clock filters
- Molads by traditional hour
- Molads by chalakim within the hour
- Mean molad versus true conjunction
- True equinox versus Rav Adda
- True equinox versus Shmuel
- Pesach and the true equinox
- Day-29 evening · illumination and altitude
- Tishri conjunction · counterfactual postponements
- Tishri · Rav Adda versus true tekufah
- Tishri · Shmuel versus true tekufah
- Tevet · Rav Adda versus true tekufah
- Tevet · Shmuel versus true tekufah
- Nissan · Rav Adda versus true tekufah
- Nissan · Shmuel versus true tekufah
- Tammuz · Rav Adda versus true tekufah
- Tammuz · Shmuel versus true tekufah
- Regular and changed haftarahs by parsha
- Haftarah distribution
- Most- and least-read sefarim and perakim
- Parsha distribution
- Single and double parshios
- Rosh Chodesh and Machar Chodesh
- Haftarahs not recited in the range
- All 14 keviyos · parshios and haftarahs
- Readings in parsha order
- Single and double readings by keviyah
- Every Shabbos in the range
- Matching molads · year details
- Matching molads · year details
- Pesach I
- Chanukah I
- Purim
- Shushan Purim
- Shavuot I
- Sukkot I
- Yom Kippur
- Tisha B’Av
- 10 Tevet
- Fast of Esther
- 17 Tammuz
- Fast of Gedaliah
- Chanukah II
- Chanukah III
- Chanukah IV
- Chanukah V
- Chanukah VI
- Chanukah VII
- Chanukah VIII
- Pesach II
- Pesach III
- Pesach IV
- Pesach V
- Pesach VI
- Pesach VII
- Pesach VIII
- Sukkot II
- Sukkot III
- Sukkot IV
- Sukkot V
- Sukkot VI
- Sukkot VII · Hoshana Rabbah
- Shemini Atzeret
- Simchat Torah
- Tu BiShvat
- Pesach Sheni
- Lag BaOmer
- Tu B’Av
- Shavuot II
- Purim Katan
- Shushan Purim Katan
- Rosh Hashanah I
- Rosh Hashanah II
- Fast of the Firstborn
- Rosh Chodesh
- Yom Kippur Katan
- Be"hab
Tools and topics
- Solar noon
- The Sun and the horizon
- Atmospheric refraction
- Location
- Observer elevation
- City radius · Neitz & Shkiya
- Obstructions
- Adjust event date
- Location & clocks
- Pesach · Nisan
- V’tein tal umatar · Diaspora
- Birchas hachama · 28-year cycle
- Water at the tekufah
- Sun · sunrise, sunset and twilight
- World map · Datelines
- Combined · space and sky
- Combined · 500 bright stars and zodiac outlines
- Combined · coordinate systems and reference planes
- Combined · labels, visibility and selection
- Combined · body sizes and distance spacing
- Combined · rotation, tilt and zoom
- Combined · astronomical event jumps
- Combined · date, time and daylight saving
- Molad search
- Core dates
- Observer location
- Civil calendars
- Sefiras HaOmer
- Tein tal umatar
- Next month’s molad
- Day’s learning
- Convert a civil date
- Planet sequence for the year
- Mazal sequence for the year
- Leap-year cycle · 19 years
- 19-year machzor
- 28-year solar cycle
- True Nisan · Tuesday night and Saturn hour
- Planetary cycle · Pirkei deRabbi Eliezer
- Zodiac cycle · mazalos
- Comparison · Shmuel, True and Rav Adda
- 28-year cycle comparisons
- Rav Adda · 28-year Saturn comparisons
- True tekufa · 28-year Saturn comparisons
- AT THE SELECTED MOMENTSun Position and Events
- Exact tekufa time
- AT THE SELECTED MOMENTSun Position and Events
- Precise adjustments
- Conjunction & molad
- Conjunction & molad ·
- Conjunction & Molad Tishri
- Days from the Jewish molad
- Moon appearance
- Moon position and events
- Sun position and events
- Planets and orbits
- Comparison · Shmuel, True and Rav Adda
- 28-year cycle comparisons
- Rav Adda · 28-year Saturn comparisons
- True tekufa · 28-year Saturn comparisons
- Leap-year cycle · 19 years
- 19-year machzor
- 28-year solar cycle
- True Nisan · Tuesday night and Saturn hour
- Planetary cycle · Pirkei deRabbi Eliezer
- Zodiac cycle · mazalos
- Molad & lunation comparison
- Month calculation
- Month length rules
- Beis din · observation
- Custom tekufa
- Tekufas Nissan & Pesach
- Compare with the standard calendar
- Calendar constraints
- The four dechiyos
- Molad Zakein · experimental rules and history
- Molad Zakein · experimental rules and history
- What is being tested?
- Custom Molad Zakein experiment
- Calendar effects · counts and extrema
- Latest molad in each month · graph
- Every year · exact values and zoom
- Derive the bounds · integer arithmetic
- Mean versus true conjunction · stored statistics
- Visual comparison
- Mean molad and solar noon
- Leap-year experiment
- True Tekufas Nissan
- Observer location
- Starting declaration
- Sighting criterion
- Leap-year criterion
- Month-length factors
- Optional postponements
- Custom anchors
- Map layers
- Settings location
- Crescent sighting · arrival deadline
- Beis Din · journey circles
- Leap-year cycle · 19 years
- 19-year machzor
- 28-year solar cycle
- True Nisan · Tuesday night and Saturn hour
- Planetary cycle · Pirkei deRabbi Eliezer
- Zodiac cycle · mazalos
- Sections
- Adam HaRishon and the early generations
- Adam HaRishon
- Before the Mabul
- The Mabul
- After the Mabul · Babel
- Period of the Avos
- Avraham and Sarah
- Yitzchak and Rivkah
- Yaakov, Rachel and Leah
- Period of the Shevatim
- Births of the Shevatim
- Mitzrayim · descent to Exodus
- The 430, 400 and 210 years
- Descent into Mitzrayim
- Passing of the Shevatim
- Yetzias Mitzrayim
- Dor Deah · Exodus to entry into the Land
- Wandering in the desert
- Entry into Eretz Yisrael
- Settlement, Judges and Kings
- Entry into the Land to the Judges
- Judges to Kings
- Period of the Kings
- Batei Mikdash and exile
- Bayis Rishon
- Babylonian exile
- Bayis Sheini
- Roman exile and the Churban
- Later history and the chain of Torah
- Post-destruction antiquity
- Zugos
- Tannaim
- Amoraim
- Geonim
- Rishonim
- Achronim
- Poskim
- Later Poskim
- The Lunar-Solar Year
- The length
- The starting alignment
- 12 months, then 13
- Sun and Moon · successive periods
- Lunar and solar periods · true and mean
- Selected measurements · detailed table
- All solar measurements beside the same lunar total
- The full 19-year cycle
- Cumulative solar and lunar days
- Solar measures − Moon · days
- Monthly breakdown
- The solar return
- Successive true conjunctions
- The moving sky
- Every day of the cycle
- Longitude and elongation · degrees
- Right ascension · degrees
- Daylight and night · hours
- Apparent solar day · seconds above/below 24 hours
- Daily numerical results
- What is being measured
- The Moon
- Moon’s hidden interval
- Selected conjunction
- Witness journey
- Monthly hidden time · before, after and total
- Each monthly conjunction · durations in days
- True molad and hidden boundaries relative to the mean Jewish molad
- Saved monthly conjunctions
Explore related concepts
About Jewish Cosmology
Jewish Cosmology is an interactive research and educational web application connecting Hebrew dates, traditional Jewish calendar calculations and halachic concepts of time with the observable motions of the Sun, Moon and planets, astronomical seasons and eclipses.
Models, terminology and limitationsHalachic times are unverified, have no rabbinic approval, and must not be relied upon for practical halachic decisions unless and until an appropriate authority approves them.