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Informations about the Birthday Moon Calculator

Moon Birthdays
The Birthday Moon Calculator calculates the moon phase at the specified birth day and the consecutive moon birthdays with the same moon phase on it. Since the moon's course is not synchronous with a solar year, the consecutive birthday moon phases do not match the birthday in the Gregorian lunisolar calendar (current calendar). Twelve lunar months are on average fewer days than twelve months in the solar calendar. To compensate to the Gregorian lunisolar calendar, leap moon months / leap lunations are inserted. Thus the moon birthdays always move around the birthday in the Gregorian lunisolar calendar.

Moon Leap Year
The Moon Birthday Calculator may not be a lunar calendar, but it uses lunar leap months for lunar leap years. However, these are not inserted directly in the month of February as in ancient times, but are generally added to a lunar year if the date of the consecutive lunar birthdays falls below a tolerance of half a lunar month to the birthday date in the lunisolar calendar. Thus, the continuous lunar birthdays move around the lunisolar calendar birthday date. If a lunar birthday date falls behind the lunisolar calendar birthday date and the next succeeding lunar birthday date falls before the lunisolar calendar birthday date, then there are 13 birthday lunar phases in that lunisolar life year. This can happen after a lunar leap year, but it does not have to.

Calculation of the moon birthdays
Calculation of the moon birthdays
If a lunar birthday falls below a tolerance of one average lunation, starting from the birthday date in the lunisolar calendar, then a lunar leap month is inserted. It is then a birthday lunar leap year. In the following lunar life year it is then possible that 13 birthday moon phases fall into this lunisolar calendar year.
1 moonyear of life = 12 lunation = ~355 days
1 moonleapyear of life = 1 moonyear + 1 moonmonth = 13 lunation (Don't confuse with 13 birthday-moonphases per one lunisolaryear of life)
1 lunisolaryear = 365 days
1 lunisolarleapyear = 366 days

Birthday moon phase
The Moon Birthday Calculator is based exclusively on lunations, starting from the birthday moon phase, and not on a lunar calendar. In the Moon Birthday Calculator a birthday lunar year has 12 or 13 lunar months with different lengths. The lengths of the birthday lunar months are not given and must be calculated by yourself. Also it is not considered whether in a lunisolar calendar 13 new moons occur in a solar year, or 13 birthday moon phases. The Moon Birthday Calculator is not based on the new moon, but exclusively on the birthday moon phase.

Click on the moon icon above for a list of all new moon dates from January 2000 to December 2100, indicating lunation variations, as well as indicating 13 new moons in a lunisolar calendar year.

New moon cycle with moon phases / lunar phases as light figures
Neumond-Zyklus mit Mondphasen. New moon cycle with illuminations.
New moon
Waxing crescent moon
First quarter moon
Waxing gibbous moon
Full moon
Waning gibbous moon
Last quarter moon
Waning crescent moon
New moon

Moon Age
A moon year / lunar year with 12 lunations / lunar months is shorter than a solar year with 12 lunisolar calendar months. A moon year / lunar year with a leap moon month, or a leap lunation, has 13 lunations / lunar months and compensates the difference to the Gregorian lunisolar calendar again. Without lunar leap months / leap lunations, the consecutive lunar birthdays in the Gregorian lunisolar calendar would move backward by ~10 days per year, passing through all months over time. A person's lunar age would thus be ~10 days shorter each year, and after 36 years, 1 year difference would be reached. In the Old Testament persons with an age of up to 1000 years are indicated. It is assumed that this did not mean moon years / lunar years or solar years, but lunar months / lunations. Methuselah died with 969 years. 969 lunations are 80 lunar years each with 12 lunar months / lunations as well as including 2 lunar leap years. In the Gregorian lunisolar calendar it is 78.2 years.

Formula to calculate the lunar month age:
Number of elapsed years of age * 12
+ Number of lunar switch years elapsed
+ Number of lunar months elapsed since last lunar birthday.
= Moon Month Age

Month names
The names of the months of a year have their origin in the moon. More precisely in the lunations of the earth moon. A lunation is a lunar cycle. During a lunation the moon orbits the earth once completely and passes through all moon phases. The moon phase is the illumination of the moon by the sun, which is visible from the earth. Today a lunation is counted from new moon to new moon. In earlier times the observation of a full moon was easier to see with the bare eye and a lunation was counted from full moon to full moon. 12 lunations have a length of ~355 days. The solar year has a length of 365.25 days, making it ~10 days longer on average than a lunar year. Ancient lunar calendars had a length of 354/355 days. The days missing from this calendar to the solar year were simply omitted. The lunar calendar of the Maya regarded the days missing to the solar year as days given by the gods, on which one was not allowed to work. With the adjustment of the lunar calendar to the solar year, the month of February was used to insert in it leap months every two years that lasted 22/23 days. In the course of time, the lunar calendar was adapted more and more to the solar year and thus became a lunisolar calendar.

The names of the months still valid today have partly a nature-related and agricultural meaning in the course of a solar year. In the Roman (lunar) calendar, the month of March was the first month of the year.

January: Janus, Roman god of the beginning and the end. Latin "ianua" (threshold). Hartung (hard/frozen), ice month/ice moon, transition month.

February: Februa, Byname of Juno (Hera), goddess of fertility. Latin "februare" (to cleanse). Hornung (antler shedding in red deer), melting month / melting moon.

[Mensis intercalaris: leap month. (until to year 44 before our era)]

March: Mars, God of vegetation, son of Juno. Latin "marte" (martial, concerning the forces of nature. lentus). Lent, Lenten, lent month / lent moon, sowing month.

April: Aphrodite (Venus), Goddess of love. Latin "aperire" (to open, concerning the opening buds). Mooding, grass moon, month of sprouting.

May: Maia, Goddess of maturity, nymph, daughter of Atlas. month of delight / moon of delight, bloom moon, flower moon.

Juny: Juno (Hera), Goddess of fertility. fallow month / fallow moon (breaking / plowing the field for winter sowing).

July: Julius Caesar, from the family of the Julians. Iulus, son of Aeneas, son of Aphrodite. Original (Latin) name of the month: Quintilis (Fifth). Hay month / hay moon.

August: Augustus, roman emperor, great-nephew of Julius Caesar. Original (Latin) name of month: Sextilis (Sixth). Harvesting, harvest month / harvest moon, ear month.

September: Latin "septem" (seven). Parting, parting month / parting moon (equinox).

October: Latin "octo" (eight). Wine month / wine moon.

November: Latin "novem" (nine). Fogginess, wind month / wind moon.

December: Latin "decem" (ten). Yule Moon (Yule, winter solstice), turning month / turning moon.


Lunar orbit – Lunation
A mean synodic lunation lasts ~29.5 days. Thereby fluctuations of ±10 hours occur. In ancient lunar calendars the months have 29 and 30 days.

The orbit of the Moon and the view of the Moon from Earth
The lunar orbit and the angle of view of the crescent moon
The orbit of the moon is not on the equator. The view of the crescent moon is different from the southern hemisphere and the northern hemisphere of the Earth. The moon is not always at the same altitude in the sky due to the inclination of the earth's axis and the inclination of the moon's orbit. Because of this, the moon rotates in the view from the earth moreover.

The lengths of the lunations / months vary. (Lunations from 01/2000 to 12/2030)
Fluctuations of Lunation Lengths. Duration of Lunation.
A mean synodic lunation of 29 days, 12 hours, 44 minutes, and 3 seconds was used as the mean (00:00).

Synodic Lunations with synodic lunation mean time lenght
Lunation From To Duration
134 06.11.2010 04:52 05.12.2010 17:36 29d12h44m
259 14.12.2020 16:17 13.01.2021 05:00 29d12h44m
289 19.05.2023 15:53 18.06.2023 04:37 29d12h44m
929 15.02.2075 06:41 16.03.2075 19:25 29d12h44m

A lunation, i.e. an orbit of the moon around the earth, is not linear in time. Since the earth moves around the sun at the same time, the moon must cover a longer distance on the side of the earth facing away from the sun and a shorter distance on the side of the earth facing the sun. Further fluctuations in time occur as the Earth moves on an ellipse around the Sun. When the Earth is closer to the Sun, it moves faster in its solar orbit and slower when it is farther from the Sun. In addition, the Earth rotates on its own axis. As a result, the Moon can never be seen from Earth in the same celestial orbit.

Representation of the orbits of the moon and the earth around the sun
Orbits of the moon and the earth around the sun
The orbit of the earth around the sun is an ellipse and moreover off center. When the Earth is closer to the Sun, it moves faster around the Sun. If the earth is more distant from the sun, then it moves slower around the sun.
The moon does not move around the earth linearly in time. The moon must keep up with the rotation of the earth around the sun. If the direction of motion of the moon is opposite to that of the earth around the sun, it is faster. If the direction of motion of the moon is equal to that of the earth around the sun, it is slower.
Aphel: farthest point from the sun (152 Mio. km)
Perihel: closest point to the sun (147 Mio. km)

Moon Phase & Moon Illumination
A "moon phase" is a complete lunation. A moon phase passes through two illumination phases. Illumination is defined as the illumination of the moon by the sun which is visible from the earth. The moon itself is like the earth always illuminated to 50% by the sun. The first illumination phase is from new moon to full moon. At new moon no illumination of the moon by the sun is visible from the earth. At full moon the complete illumination of the moon by the sun can be seen. The first illumination phase is the first half of the moon phase. The second illumination phase, from full moon to new moon, is the second half of the moon phase. At new moon, the moon is on the side of the earth facing the sun. At the full moon, the moon is on the side of the earth away from the sun. The reason the new moon and full moon can be seen from Earth is because the Earth's axis and the moon's orbit are tilted. During a solar eclipse, the Moon is exactly between the Earth and the Sun - the Sun is covered by the Moon, or the Moon casts its shadow on the Earth. In a lunar eclipse, the Earth is exactly between the Sun and the Moon - the Earth obscures the Moon, or the Earth casts its shadow on the Moon.

Illustration of the lighting (illumination) of the moon visible from the earth
Lighting illumination from the moon
The sun always illuminates a whole half of the moon's surface. From the earth this can be seen only at full moon. Due to the rotation of the moon around the earth, most of the time only a part of the moon's illumination can be seen from earth.
From the northern hemisphere, the illumination of the Moon visible from Earth moves from right to left. From the southern hemisphere, the illumination of the Moon visible from Earth moves from left to right.

The obliquity of the lunar orbit
The Moon's orbit deviates from the Earth's celestial equator from 18.4° (Lunar Minor) to 28.6° (Lunar Major) in a period of 18.6 years (in 9.3 years from 18.4° to 28.6°).
Obliquity of the lunar orbit - lunar orbit
The obliquity of the moon's orbit in relation to the earth's equator / celestial equator

Moon rotation from moonrise to moonset
Moon rotation from moonrise to moonset as optical illusion
The moon rotates from moonrise to moonset and with it its illumination. The magnitude of the moon's rotation depends on the observer's location on Earth. This moon rotation is an optical illusion. Not the moon rotates, but the earth. The rotation of the moon is caused by the rotation of the earth around its own axis.
The obliquity of the lunar orbit produces a maximum variation of the lunar maximum (upper culmination) of 57.2° (±;28.6°) in total. This is the reason why the moon cannot be seen from locations north of latitude 61.4 (90° - 28.6° = 61.4°) or south of latitude -61.4 at certain times on some days, because it does not come above the horizon there, or can be seen all the time, because it does not dip below the horizon. This is further the reason that at certain times on some days the moon can be seen in the southern sky at locations south of the equator to latitude -28.6, or can be seen in the northern sky at locations north of the equator to latitude 28.6. At these celestial phenomena at a location between latitude 28.6° and -28.6° the moon rotation from moonrise to moonset is especially large and especially fast when passing the moon's peak (upper culmination). If the own location is during a moon peak (upper culmination) exactly under the moon, or on the moon orbit, so the moon stands at its peak (culmination) exactly above the own location with 90° to the horizon, then the moon rotates from there together with illumination when wandering through its peak (culmination) in only a few minutes around 180°. If the own location is at certain times on the latitude 28.6 or -28.6, then the rotation of the moon can be 270° from moonrise to moonset. On the other hand, the moon rotates less and less, the more northern or southern the own location is as well as at north pole and south pole only minimally.

The following rule applies across the board (exceptions excluded):
If the moon rotates clockwise, the own location is north of the moon orbit.
If the moon rotates counterclockwise, the own location is south of the moon orbit.
If the moon rotates very slowly and gradually over the whole visible time above the own location, the own location is far away from the moon orbit. The slower and the less the moon rotates from the own location, the further the moon orbit is from the own location.
If the moon rotates over the own location only in a short time interval and in it very fast and far, the own location is very close to the moon orbit. The shorter the time period and the faster and farther the rotation, the closer is the moon orbit from the own location.

The following are views of the Moon from various locations including two special locations.

How many images from the image series can be seen from the own location on Earth depends on how far away the own location is from the lunar orbit. The outer images are considered if the own location on earth is on the moon orbit.

The lunar rotation from moonrise to moonset north of the lunar orbit and south of the equator
Moon rotation from moonrise to moonset north of lunar orbit
The two moons respectively on the right and on the left can appear if the own location is north of the equator and the moon orbit is south of the own location or even on the moon orbit.

The lunar rotation from moonrise to moonset south of the lunar orbit and north of the equator
Moon rotation from moonrise to moonset south of lunar orbit
The two moons respectively on the right and on the left can appear if the own location is south of the equator and the moon orbit is north of the own location or even on the moon orbit.

moonphase
Theoretical visualization






Moon pictures: NASA & Bdaymoon.com
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