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You are at the section Calendar History

Lining Up Julian Period Day Between Earth and Mars

While the creation of a calendar for Mars has been in discussion, one thing that needs to be agreed on is to create a Mars version of a Julian Period Day, or what I call the Martian Period of Mars Day.

So I decided to line up the Martian Period of Mars Day of 0.00000 with the exact Julian Period Day of 0.00000 when it was 12pm on January 1, 4713 B.C. and from that point are where both periods begin counting up forwards.

The question remains on what basis would the Martian Period of Mars Day would increment? To make it change on the same date as the Julian Period Day would be redundant, so instead, I would increment it by 1.0 for every 1.02749125170 Earth days since the Martian Day (or Sol) is longer than Earth's by 39 minutes and 35.244147 seconds.

Determining Martian Period of Mars Days

Like the Julian Period Dating, the Martain Period Dating is independent of year, month and week. It doesn't care how many revolutions around the sun it achieved.

The Martian Period of Mars Day will reflect the time on their version of the Greenwich Meridian Time at zero degrees longtitude, whereever that may be. We don't know but that's not important for our purpose.

For each Julian Period Day on Earth, note that the new day begins at noon local time. We'll say that the numbers converted to the Martian Period of Mars Day will be at noon on Earth time.

Julian Period Day 0.000 began at noon on January 1, 4713 B.C Julian-1 calendar, or January 1, -4712 Julian-1 year decimalized.

Converting between Julian Period Day, Julian Period Year, Martian Period of Mars Day and Martian Period of Earth Year

CAUTION: The Julian-1 year is NOT the Julian Period Year!

To convert from the Julian Period Day to the Martian Period of Mars Day...

Julian Period Day ÷ 1.02749125170 (the length of the Martian sol in Earth Days)

MPMD = JPD / 1.02749125170

For example, January 1, 2016 Julian-1 Date (or January 14, 2016 Gregorian Date) corresponds to Julian Period Day 2457402. To get the Martian Period of Mars Day, divide 1.02749125170 into 2457402 and you get 2391652.479701594.

A recap: To convert from the Julian Period Day to the Julian Period Year...

Julian Period Day ÷ 365.25

JPY = JPD / 365.25

To convert from the Julian Period Day to the Martian Calendar of Earth Year, which is the same thing as the Martian Synodic Year...

Julian Period Day ÷ 686.97258

MCEY = JPD / 686.97258

This formula below should give the same result:

To convert from the Martian Period of Mars Day to the Martian Period of Mars Year, which is the same thing as the Martian Synodic Year...

Martian Period of Mars Day ÷ 668.592018

MPMY = MPMD / 668.592018

With this formula, Julian Period Day 687 would be Martian Period of Earth Year 1.00003991425684

January 1, 2016 Julian-1 Date (or January 14, 2016 Gregorian Date) corresponds to Julian Period Day 2457402.

To get the Martian Period of Earth Year, divide 686.97258 into 2457402 and you get 3577.147140283241.

To get the Julian Period Year, divide 365.25 into 2457402 and you get 6728. To get the Julian-1 Year, subtract 4712 from 6728 to get 2016.


  1. Days
    1. The Length of Martian day is called a sol.
    2. Its sidereal day is 24 hours 37 minutes and 22.663 seconds. (corresponds to Earth with 23 hours 56 minutes and 4.0916 seconds)
    3. Its synodic day is 24 hours 39 minutes and 35.244147 seconds. (corresponds to Earth with 24 hours 00 minutes and 00.002 seconds)
    4. One Martian Sol (day) equals 1.02749125170 Earth days
  2. Years
    1. The length of Martian year is 686.97258 Earth synodic days or 668.592018 Martian synodic sols.
    2. One Earth synodic year equals approximately 365.24218967
    3. One Martian synodic year equals approximately 1.880876030835017 Earth synodic years.
Calendar History Main Page Calendar 1: The Romulus Calendar I Calendar 2: The Republican Calendar I Calendar 3: The Republican Calendar II Calendar 4: The Republican Transitional Calendar Calendar 5: The Julian-Roman-Actual-1 Calendar Calendar 6: The Julian-Roman-Transitional-1 Calendar Calendar 7: The Julian-Roman-1 Calendar Calendar 8: The Julian-Kalends-1 Calendar Calendar 9: The Julian-1 Calendar Calendar 10: The Gregorian Calendar Dual Dating Date Confusion Definition of Days on the Calendars Definition of Calendars: Others Old, New and Unknown Styles Leap Year Error on the Julian-Roman-Actual-1 Calendar What Calendars Each Country Was Using Gregorian-Julian Differences By Century New Years Days Addenda Day and Year Measurements Calendar Varieties-Gregorian Calendar Varieties-Julian Calendar Varieties-Other Years Converted From Julian Period Day Lining Up Julian Dates Between Earth and Mars The Martian Calendar of Earth Converting From the Julian Period Date Creating a Julian Period Day Database File Truncating Answers Conversion Between Julian-1 and Gregorian Calendars Create a Calendar Leap Year Day Comparisons Swedish Calendar 1700-1712 Fractions of Years, Etc.
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