NB: The latitude of a location can change the dates of the equinox and the new moons.
How to construct God's Calendar and determine dates for the Holy Days:
One: God says that the heavenly lights were given to determine seasons, days and years. These are heavenly objects which are observable without the need for any complicated instrumentation or technology.
Gen 1:14 Then God said, Let there be lights in the firmament of the heavens to divide the day from the night; and let them be for signs <226>, and seasons <4150>, and for days and years; [NKJV].
Using Strong's Complete Word Study and given the context, this second part of verse 14 would be better rendered as follows:
and let them be for signs <226>, and for seasons, the appointed feasts <4150>, and for days, and years:
1. All four signs mentioned in Gen 1:14 are, in fact, cycles and it is the intention of the Calendar to use this information to determine when the appointed Feast cycles of God begin each year and when each Festival occurs during that cycle. This language is most easily seen in reference to the Feast of Tabernacles (Feast of Ingathering/Final Harvest in Ex 23:16, Ex 34:22 and Deut 16:13) where most translations render the word "Shaneh" (Strong's 8138) as "year". This word is from "shanah" which means to repeat or do again a cycle if you will. Rendering "shaneh" as year makes no sense as the year, which is a complete annual cycle, will will not end until the next March equinox. However, it is the end of the crop harvesting season, which is a cycle, and it is at the end of the Biblical Holy Day season, another cycle in the year. The NLT correctly renders this phrase as "at the end of the harvest season", which refers to an independent cycle within the annual cycle.
2. SIGNS: Signals or markers, such as the March Equinox. This is the solar boundary between the end of winter and the start of summer (Psa 74:17) in the northern hemisphere.
3. DAY: One complete rotation of Earth on its axis, which is one complete cycle of Earth's rotation. A day starts in the evening and ends when the next day starts the following evening. One full day, rotation of Earth, being 24 hours, where the light part of the day is 12 hours and the dark part is 12 hours (John 11:9-10).
4. WEEK: The word translated as "week" (shabuwa, Strong's 7620) means a period of seven and whether the word refers to days or years is determined by the context. In determining the Sabbath (Gen 2:2-3) it is clear from the context that a week is a cycle of seven days seven full periods of dark and light, or seven full rotations of Earth, then the weekly cycle starts again.
5. MONTH: One full revolution of the moon around Earth, then the cycle starts again.
6. YEAR: More accurately translated as "cycle", which is the cycle from one point in the year to the same point in the next year. Biblically, the beginning of the year starts and ends with an equinox, as revealed by God in Psa 74:17 (also see point 1 above)..
NOTE: Nowhere in the Bible does it say that crops are to be used for the determination of seasons! God says that the lights in the heaven (sun and moon in particular) are to be used for the determination of the seasons the instruction is very specific and there is no mention of crops. The early Hebrew calendar was faithful to this instruction, but the Jewish calendar, introduced by Hillel the II in the third century A.D., incorrectly also uses crops as a determinant for calculating 1 Abib. Also, nowhere in the Bible does it state that the first day of the first month has to coincide with the first day of the summer season. This means that both the annual and monthly cycles must end before a new cycle of months can be declared.
Two: Biblically, the year is divided into two parts summer and winter (spring and autumn being added by man as transition periods) with the March and September equinoxes marking the boundaries between these two major seasons (Psa 74:17). During an astronomical equinox, when the geometric centre of the sun is directly above Earths equator, the length of day and night can be significantly different. However, with an observed equinox the length of day and night are almost the same (equinox meaning equal night) and therefore can be determined easily by using a simple sundial. The Biblical evidence shows that simple solar and lunar observation is to be the method used in calculating the Hebrew Calendar dates and therefore it is the "observable equinox" that is to be used as the method of measurement, not the "calculated equinox". When day and night are approximately the same length, using the appearance and disappearance of the solar disk, we have an equinox. The exact day on which the new year is to begin is the first new moon after the equinox, as explained in point 4 below.
Three: Each month is to begin with the sighting of the first crescent of the new moon by the unaided eye the Hebrew for month is "chodesh", with the root meaning of new thing. Remembering here that God says the "Lights" in heaven are to be used to determine seasons, days and years, NOT the "darkness" or when the moon cannot be seen such as in a lunar conjunction. Using this method of actually sighting the new crescent moon, it is a simple thing to determine the 1st day of the 1st month (1 Abib Ex 12:2). Modern astronomy has taken on the practise of calling the lunar conjunction the new moon, when it is darkest, but a dark moon cannot be seen (it is not observable) and therefore has not yet become something new as well as it not being a heavenly "light" at this time. God says that the lights in heaven are to be used for the determination of seasons and times, NOT the darkness. The month of Abib means "green ears" of grain and therefore it is the first new moon after the March equinox (northern hemisphere) which starts the Biblical cycle of months.
Four: Each new year begins on the first sighting of the new moon (small crescent) after the March equinox. The equinox indicates when a new cycle of months is about to begin, with the exact 1st day of the new cycle being given by the first new moon after the equinox after completion of the previous year. The first new moon will always be after the equinox, because even if the new moon is that very evening, then Biblically it will be the next day because Biblical days start at evening (not midnight). There are some who begin the new year with the new moon closest to the March equinox even though it may be before the equinox. However, it is neither reasonable nor Biblical (see "Equinox" below) to have the first month of the year begin before winter of the previous yearly cycle) has ended.
Five: Each Biblical day begins at evening, not at midnight (Gregorian Calendar) and accordingly when a Roman day is cited, the intent is that the Biblical day commences the evening before. For example, the Roman day of 10 January will commence (Biblically) at sunset (evening) on 9 January.
Six: Sunrise and sunset are when the top of the solar disk first appears above the horizon to start the day and when the top of the solar disk disappears below the horizon to start the night. As official equinox times are calculated using the geometric centre of the solar disk as it passes over the equator, rather than using equal length of day and night, there can be a difference of several days between an astronomical equinox and an observed equinox.
Seven: Currently, some elements associated with festival observance in Jerusalem are done through convenience rather than correct observance of the Word of God and therefore festival observances are not always on the correct days. Until the restoration of all things (including setting the cosmological clock in order) upon the return of Christ, all times should be determined through local observations, not coordinated with observed Jerusalem times. God began to reveal His Holy Days to Israel while they were still in Egypt. Moses did not use Jerusalem time and for forty years we can be sure Israel did not use Jerusalem time. Moses used local time. Jerusalem did not become of any significance until the time of King David, yet the Holy Days were being observed well before he was born. In fact there is no command in the Bible specifying that Jerusalem time should be used. Since God is constant in all things it is reasonable to conclude that He expects His people to observe seasons and appointed times properly in this present day as they apply locally. Those observations do not include coordination with solar or lunar sightings in another country half way around the world. At the return of Christ, the restoration of all things will take place and part of that restoration will be correcting the orbits of both Earth and the Moon to form the basis of a correct calendar.
Eight Constellations: While the sun and moon were responsible for determination of the Hebrew Calendar and therefore responsible for determination of the annual Holy Days, in Job 38:31 there is evidence that the constellations played a role in identifying the type and duration of certain physical seasons of the year. The Pleiades appears to be mentioned in connection with the spring or vernal season, while Orion is mentioned in connection with the colder and less fruitful months of the cycle (year) in the northern hemisphere Orion may be seen in the morning, towards the end of October and is visible through November, December and January. The full meaning and use of constellations in agriculture, animal husbandry, fishing and hunting is not now clear, but it seems that they were intended to guide man in his physical survival activities throughout the yearly cycle. For example, the appearance of certain constellations would coincide with deer and bird migrations, while others coincided with the run of different species of fish, both sea and river. This reality is a perfect type of the angels as stars, whose primary duty is to be ministering spirits to the heirs of salvation (helpers in the everyday lives of humans).
The following Table from http://www.timeanddate.com/astronomy/equinox-not-equal.html shows how latitude affects the date on which an equinox falls, thereby showing the importance of local observations of time when determining the start of the first month of the Biblical year, which is the first new moon (first visible crescent after the equinox). Even if day and night arent exactly equal on the day of the equinox, there are days when day and night are both very close to 12 hours. However, this date depends on the latitude, and can vary by as much as several weeks from place to place. The Table below shows approximate dates for when day and night are as similar as possible according to latitude. On the equator, the day and night stay approximately the same length all year round. Sunrise is defined as the instant when the upper edge of the sun's disk becomes visible above the horizon not when the centre of the sun is visible. In the same sense, sunset refers to the moment the upper edge disappears below the horizon.
Sunrise and sunset times were obtained from the World Clock at http://www.timeanddate.com/worldclock/, where the sunrise and sunset times are in accordance with the appearance and disappearance of the solar disk, not the sun's geometric centre. The equinox dates are therefore based on observation, not calculation.
Also referenced was the Astronomical Institute / Utrecht University via http://www.astro.uu.nl/~strous/AA/en/antwoorden/zonpositie.html
Phases of the moon were obtained from the University of Texas McDonald Observatory via
1. "Gods Perfect Calendar" by Evidence of Truth
2. Is 1 Abib the first Crescent Moon on or after the Equinox? by The Congregation of Yahweh
Links to other sundial sites:
http://www.nmm.ac.uk/make-your-own/sundial (Good demonstration and templates)
http://solar.physics.montana.edu/ypop/Classroom/Lessons/Sundials/sundials.html (Recommended site - make a sundial necklace/keychain).
The equinox is mentioned in Psa 74:17 as one of theborders of Earth set by God. Also, it is being obedient to God's command to base all calendar calculations on the heavenly lights (Gen 1:14), which makes the calendar accurate for the whole year including setting the right time of the year for the seventh month the Feast of Ingathering season.
Then God said, Let there be lights in the firmament of the heavens to divide the day from the night; and let them be for signs, and seasons, and for days and years; [NKJV].
"...Thine is the day, also Thine is the night, Thou hast prepared a light giver the sun. Thou hast set up (all the) borders of earth, summer and winter Thou hast formed them..." [YLT]
Note that summer and winter are mentioned in direct context with"borders of earth" God has set. Although God has set ALL the borders of earth, the only borders being spoken of here are in connection with summer and winter and those borders are the equinoxes. These borders for the seasons are determined by the great heavenly light (the sun) and this is in accordance with the decree in Gen 1:14 that the lights in heaven determine the seasons and years.
There are still many who rely on the Jewish calendar, which is bases the beginning of the year on crops rather than God's clear command in Gen 1:14, that all calendar calculations shall be based on the heavenly lights (sun, moon and stars). The equinoxes are the natural dividers between the two great seasons of summer and winter they are the God-given sign of season division by the sun. If we are to base calendar calculations on when certain crops mature in March, then it is not only disobedience to God's clear command, a crop based calendar will always have the year starting in spring (northern hemisphere), but when this method causes the year to begin before the March equinox (as in 2013) the festival of ingathering season, which starts with the Feast of Trumpets, will commence before the ingathering of all crops has taken place. The ingathering is supposed to be completed before festival time so the people could travel to the festival site and enjoy the fruits of the land with which God had blessed them. However, an early false start to the year before the March equinox would result in the crops being left in the field while the people were attending the "Feast". It would still be summer, the crops would be ready to harvest, but nobody to do the harvesting. There would be little with which to celebrate at the Feast of ingathering and the people would be concerned about their crops instead of enjoying the festival of God.
"... Finally, celebrate the Festival of the Final Harvest at the end of the harvest season, when you have harvested all the crops from your fields."
"... and celebrate the Festival of the Final Harvest at the end of the harvest season.
Deut 16:13 (NLT)
"You must observe the Festival of Shelters for seven days at the end of the harvest season, after the grain has been threshed and the grapes have been pressed."
It is therefore crucial for the calendar to be applicable for the whole year, not just the beginning and the only way it is assured always to be applicable for the whole year is for the start of the year to be determined by the lights in heaven, NOT crops the year must commence on or after the March equinox, not before.