Darian calendar

The Darian Calendar is a system of time-keeping designed to serve the needs of any possible future human settlers on the planet Mars. It was created by aerospace engineer and political scientist Thomas Gangale in 1985 and named by him after his son Darius.

Contents

1 Year Length and Intercalation 2 Calendar layout 3 Start of Year 4 Disputed points 5 Martiana Calendar 6 Other Darian Calendars 7 See also 8 External links

Year Length and Intercalation

The basic time periods from which the calendar is constructed are the Martian solar day (sometimes called a sol) and the Martian vernal equinox year, which is slightly different from the tropical year. The sol is 39 minutes 35.244 seconds longer than the Terrestrial solar day and the Martian vernal equinox year is 668.5907 sols in length. The basic intercalation formula therefore allocates six 669-sol years and four 668-sol years to each Martian decade. The former (still called leap years even though they are more common than non-leap years) are years that are either odd (not evenly divisible by 2) or else are evenly divisible by 10.

Calendar layout

The year is divided into 24 months. The first 5 months in each quarter have 28 sols. The final month has only 27 sols unless it is the final month of a leap year when it contains the leap sol as its final sol.

The calendar maintains a seven-sol week, but the week is restarted from its first sol at the start of each month. If a month has 27 sols, this causes the final sol of the week to be omitted. This is partly for tidiness. It can also be rationalised as making the average length of the Martian week close to the average length of the Terrestrial week, although it must be remembered that 28 Earth days is roughly equal to 27+1/4 Martian sols and not 27+5/6 Martian sols.

In the following table, the days of the week are Sol, Luna, Mars, Mercurius, Jupiter, Venus, Saturnus.

Sagittarius								Dhanus								Capricornus
So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa
1	2	3	4	5	6	7		1	2	3	4	5	6	7		1	2	3	4	5	6	7
8	9	10	11	12	13	14		8	9	10	11	12	13	14		8	9	10	11	12	13	14
15	16	17	18	19	20	21		15	16	17	18	19	20	21		15	16	17	18	19	20	21
22	23	24	25	26	27	28		22	23	24	25	26	27	28		22	23	24	25	26	27	28
Makara								Aquarius								Kumbha
So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa
1	2	3	4	5	6	7		1	2	3	4	5	6	7		1	2	3	4	5	6	7
8	9	10	11	12	13	14		8	9	10	11	12	13	14		8	9	10	11	12	13	14
15	16	17	18	19	20	21		15	16	17	18	19	20	21		15	16	17	18	19	20	21
22	23	24	25	26	27	28		22	23	24	25	26	27	28		22	23	24	25	26	27
Pisces								Mina								Aries
So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa
1	2	3	4	5	6	7		1	2	3	4	5	6	7		1	2	3	4	5	6	7
8	9	10	11	12	13	14		8	9	10	11	12	13	14		8	9	10	11	12	13	14
15	16	17	18	19	20	21		15	16	17	18	19	20	21		15	16	17	18	19	20	21
22	23	24	25	26	27	28		22	23	24	25	26	27	28		22	23	24	25	26	27	28
Mesha								Taurus								Rishabha
So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa
1	2	3	4	5	6	7		1	2	3	4	5	6	7		1	2	3	4	5	6	7
8	9	10	11	12	13	14		8	9	10	11	12	13	14		8	9	10	11	12	13	14
15	16	17	18	19	20	21		15	16	17	18	19	20	21		15	16	17	18	19	20	21
22	23	24	25	26	27	28		22	23	24	25	26	27	28		22	23	24	25	26	27
Gemini								Mithuna								Cancer
So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa
1	2	3	4	5	6	7		1	2	3	4	5	6	7		1	2	3	4	5	6	7
8	9	10	11	12	13	14		8	9	10	11	12	13	14		8	9	10	11	12	13	14
15	16	17	18	19	20	21		15	16	17	18	19	20	21		15	16	17	18	19	20	21
22	23	24	25	26	27	28		22	23	24	25	26	27	28		22	23	24	25	26	27	28
Karka								Leo								Simha
So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa
1	2	3	4	5	6	7		1	2	3	4	5	6	7		1	2	3	4	5	6	7
8	9	10	11	12	13	14		8	9	10	11	12	13	14		8	9	10	11	12	13	14
15	16	17	18	19	20	21		15	16	17	18	19	20	21		15	16	17	18	19	20	21
22	23	24	25	26	27	28		22	23	24	25	26	27	28		22	23	24	25	26	27
Virgo								Kanya								Libra
So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa
1	2	3	4	5	6	7		1	2	3	4	5	6	7		1	2	3	4	5	6	7
8	9	10	11	12	13	14		8	9	10	11	12	13	14		8	9	10	11	12	13	14
15	16	17	18	19	20	21		15	16	17	18	19	20	21		15	16	17	18	19	20	21
22	23	24	25	26	27	28		22	23	24	25	26	27	28		22	23	24	25	26	27	28
Tula								Scorpius								Vrishika
So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa		So	Lu	Ma	Me	Jo	Ve	Sa
1	2	3	4	5	6	7		1	2	3	4	5	6	7		1	2	3	4	5	6	7
8	9	10	11	12	13	14		8	9	10	11	12	13	14		8	9	10	11	12	13	14
15	16	17	18	19	20	21		15	16	17	18	19	20	21		15	16	17	18	19	20	21
22	23	24	25	26	27	28		22	23	24	25	26	27	28		22	23	24	25	26	27	28

The last day of Vrishika is an intercalary day that does not occur in every year.

Start of Year

The Martian year is treated as beginning near the equinox marking spring in the northern hemisphere of the planet. Mars currently has an axial inclination similar to that of the Earth, so the Martian seasons are perceptible, though the greater eccentricity of Mars' orbit about the Sun compared with that of the Earth means that their significance is strongly amplified in one hemisphere and masked in the other. The most sophisticated calculations of the Darian calendar extend to the point of making allowance for the slight increase in the length of the Martian vernal equinox year over several thousand years. These prescribe a more complicated intercalation formula (for details see the link cited below).

Disputed points

Certain details of the Darian calendar have been the subject of dispute. The greatest of these disputes surrounded the selection of the Martian epoch. Originally this was chosen as late 1975 in recognition of the American Viking program as the first fully successful soft landing mission to Mars. This selection came to be seen as excessively parochial, and also resulted in the many telescopic observations of Mars over the past 400 years being relegated to negative dates. The currently favoured epoch, first suggested by Peter Kokh, is in 1609 in recognition of Johannes Kepler's use of Tycho Brahe's observations of Mars to elucidate the laws of planetary motion, and also Galileo Galilei's first observations of Mars with a telescope.

Nomenclature has also been a subject of dispute, although with somewhat less rancor. The names of the 24 months were provisionally chosen by Gangale as the Latin names of constellations of the zodiac and their Sanskrit equivalents in alternation. The 7 sols of the week, similarly, were provisionally named after the Sun, Moon and the 5 brightest planets as seen from Mars - including the Earth. These choices were also criticized as parochial. As a result, several alternate calendars, identical in design but differing in nomenclature, have been proposed. The Darian Defrost Calendar, for instance, creates new names for the Martian months out of patterns relating letter choice and name length to month order and season. The Utopian Calendar, devised by the Mars Time Group in 2001, has additional suggestions for nomenclature modification.

The calendar does not preserve the cycle of the days of the week. This would be unacceptable for members of religions that include the seven-day week in their beliefs. It was these religious grounds that prevented the adoption of the World Calendar. It would also be unacceptable for secular people accustomed to a two-day weekend, because the omitted day is always the Martian equivalent of Saturday.

Martiana Calendar

In 2002 Gangale devised a variant of the Darian calendar that reconciles the months and the sols of the week in a repeating pattern and removes the need to omit days of the week. In the Martiana variant, all the months in a given quarter begin on the same sol of the week, but the sol that begins each month shifts from one quarter to the next.

The following table shows the sol of the week on which each month in the quarter begins. The first quarter corresponds to spring in the Martian northern hemisphere and autumn in the Martian southern hemisphere.

	First quarter	Second quarter	Third quarter	Last quarter
Even-numbered years	Sol Solis	Sol Saturni	Sol Veneris	Sol Jovis
Odd-numbered years	Sol Mercurii	Sol Martis	Sol Lunae	Sol Solis

The leap sol occurs at the end of odd-numbered years as in the original Darian calendar. Since the last month of odd-numbered years contains 28 sols, the following year also begins on Sol Solis, resulting in a two-year cycle over which the relationship of the sols of the week to the months repeats. The sol that is added every tenth year is epagomenal (not counted as part of the week), thus the two-year rotation of the sols of the week is not disrupted. The Martiana scheme avoids the Darian calendar's need to shorten the week to six sols three to four times per year. The disadvantage is that the scheme results in a two-year cycle for reconciling the sols of the week and the months, whereas the Darian calendar is repeatable from month to month.

Other Darian Calendars

In 1998, Gangale adapted the Darian calendar for use on the four Galilean moons of Jupiter discovered by Galileo in 1610: Io, Europa, Ganymede, and Callisto. In 2003, he created a variant of the calendar for Titan.

See also

• Astronomy on Mars
• Timekeeping on Mars

External links

• The Darian Calendar (http://www.martiana.org/mars/mst/darifrm.htm)
• The Calendars of Jupiter (http://www.martiana.org/mars/jupiter/jupifrm.htm)
• The Darian Calendar for Titan (http://www.martiana.org/mars/saturn/Darian_Titan_frm.htm)

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