A page from the "Calendars" exhibit...

Some Future Calendars

Modern schemes for reform?

The current calendar is not without defects, and reforms are still being proposed. Astronomically, it really calls for no improvement, but the seven-day week and the different lengths of months are unsatisfactory to some. Clearly, if the calendar could have all festivals and all rest days fixed on the same dates every year, as in the original Julian calendar, this arrangement would be more convenient, and two general schemes have been put forward–the International Fixed Calendar and the World Calendar.

The International Fixed Calendar is essentially a perpetual Gregorian calendar, in which the year is divided into 13 months, each of 28 days, with an additional day at the end. Present month names are retained, but a new month named Sol is intercalated between June and July. The additional day follows December 28 and bears no designation of month date or weekday name, while the same would be true of the day intercalated in a leap year after June 28. In this calendar, every month begins on a Sunday and ends on a Saturday.

It is claimed that the proposed International Fixed Calendar does not conveniently divide into quarters for business reckoning; and the World Calendar is designed to remedy this deficiency, being divided into four quarters of 91 days each, with an additional day at the end of the year. In each quarter, the first month is of 31 days and the second and third of 30 days each. The extra day comes after December 30 and bears no month or weekday designation, nor does the intercalated leap year day that follows June 30. In the World Calendar January 1, April 1, July 1, and October 1 are all Sundays. Critics point out that each month extends over part of five weeks, and each month within a given quarter begins on a different day. Nevertheless, both these proposed reforms seem to be improvements over the present system that contains so many variables.

Other planets

What is the length of the day and the year on other planets? If astronauts from our planet were to colonize Mars or Venus, what would be the basis for their calendar? Following is basic information about the other planets in our Solar System.

PlanetHow much sun?How different are summer and winter?How long is the year?How long is the day?
Average distance from Sun (in AU)Obliquity (tilt of axis in degrees)Revolution period (length of year in Earth time)Rotation period (length of day in Earth time)
Mercury0.387087.97 days58.65 days
Venus0.723178224.7 days243.0 days (retrograde)
Earth123.4365.26 days23.93 hours
Mars1.52425686.98 days1.026 days
Jupiter5.2033.0811.86 years9.8 hours
Saturn9.53926.729.46 years10.2 hours
Uranus19.1897.984 years17.9 hours
Neptune30.0629.6164.8 years19.1 hours
Pluto39.53122.5247.7 years6.39 days

Note: Revolution periods are sidereal periods

The obliquity (the magnitude of the axial tilt) controls the degree of seasonality, that is, the difference between summer and winter temperatures in on hemisphere. It is defined as the angle between the celestial equator and the ecliptic. The larger the tilt, the greater the seasonality. Changes in axial tilt are reflected in the size of the polar regions, the regions wherein the Sun is below the horizon for at least one full day each winter and above the horizon for at least one full day each summer. A larger axial tile means a larger polar region. A larger polar region will generally have colder temperatures toward the center of the region.

Following are details about a proposed calendar for Mars.

Mars Lander

Mars Lander 1 Site

Big Joe, the large rock just left of center is about 2 m (7 ft) wide. The top of the rock is covered with red soil. Those portions of the rock not covered are similar in color to basaltic rocks on Earth. This rock may be a fragment of a lava flow that was later ejected by an impact crater. The red color of the rocks and soil is due to an abundance of oxidized iron in the eroded material.


What should be the calendar for the planet Mars? How will future human inhabitants organize their lives? Some futurists have suggested that the Martian calendar be inspired by the common Gregorian calendar. This is their proposal.

On Earth, calendars indicate when to expect a change in seasons; helping farmers to plant, and priests to prepare festivals. Similarly, mankind on Mars will have seasons. In fact, seasonal changes on the red planet are much more severe than on Earth. By comparing Gregorian and Martian Calendars, explorers and settlers can celebrate special days, whether civil or ceremonial, at the same time as they are being observed on the home planet. Planning for the future is extremely critical for Martian endeavors in order to ensure that needed provisions will be on hand in a timely manner.

Because features of the Martian Calendar match those of the Gregorian, it is easy to compare time intervals between the two planets. One way this similarity has been provided is that we use the same words for generic units of Martian time measurement as we do for comparable earthly periods. We speak of a Martian year, quarter, month, week and day rather than using terminology that is unique to Mars. Also, days on both planets are divided into hours, minutes and seconds. Many of these time periods are further divided into the same number of parts on both Earth and Mars. Their actual lengths, of course, are not identical.

Another aid to understanding correspondence between the two calendars is because they are formed with the same structure. A red planet day is very close in length to Earth’s day. Therefore, the seven-day Mars week is very close in length to a terrestrial week. But both the beginning and extent of these short-term periods is different because the two planet’s natural days are not synchronized.

One of the Gregorian Calendar’s most rational features is its division of the year into 12 months. Because the number of months totals 12, a Gregorian year can be divided into two halves of six months and/or four quarters of three months each for planning purposes.

A natural year on Mars is almost twice the length of one on Earth. Therefore, a twelve-month Martian calendar would have resulted in month lengths of almost twice as many days as calendars have on Earth. This would have made comparisons between terrestrial and Martian months misleading at best.

An easy resolution of this problem resulted from assigning 24 months to the Martian calendar, giving them lengths of mostly 28 days—very comparable to months on Earth. Further, this 24-month calendar lends itself to division into equal periods of not only halves and quarters, but also eighths. Incidentally, an eighth of the Martian calendar is very close in elapsed time to an Earth year’s quarter.

Martian Calendar years are kept in synchronization with nature simply by beginning each new calendar year on the day of the vernal equinox, regardless of how early or late its hour might be. Most Martian Calendar years have 669 days but others have 668.

Because a prior year’s length is terminated at the start of a new solar year, leap year rules are not required. For all practical purposes, the length of any Martian Calendar year, either past or future, can be calculated from Mar’s year length and the day and time of any recent Martian vernal equinox.

To prevent confusion between various expressions of what might be either a terrestrial or Martian Calendar date, names for specific Martian days and months as well as numbers for their years are different from those used on Earth. However, days of the Martian week are named after solar system members just as they are on the home planet.

Martian days were named with these heavenly objects in mind: Sun, Phobos, Deimos, Earth, Venus, Jupiter and Saturn. Actual names of most of the seven are borrowed from roots of these object’s names in various languages (and combined with the English suffix"day.") These names are not likely to be confused with those of an Earth day.

Month’s were named to honor individuals who either participated in early space exploration or who contributed to mankind’s understanding of science. Two of the 26 alphabet letters had to be omitted, as were names of many individuals who deserved to be remembered this way.

Martian months are named in alpha sequence from Aldrin thru Zubrin as an aid for those who might find it difficult remembering the order of all 24 months. A fairly good idea of each month’s location in the year can be had by envisioning where the first letter of its name fits within the alphabet.

Listed in the following table is the length in days of all Martian Calendar months. It is not intended to serve as a calendar, but rather illustrates lengths of major subdivisions of the year. Most calendar years have month lengths as shown. Of those that don’t, the only difference from values given is that their year ends after the 27th day of the 24th month.

How many days in a Martian month?
1st Quarter2nd Quarter3rd Quarter4th Quarter
Month NumberNumber of DaysMonth NumberNumber of DaysMonth NumberNumber of DaysMonth NumberNumber of Days

Note that the length of all major divisions of the Martian Calendar year including the month, eighth, quarter and half, are either identical to, or within a day of, that of any other comparable time period. This congruence is critical to the use of accumulated Martian statistics for planning future red planet activities



A harsh desert world orbiting the twin suns Tatoo I and Tatoo II, this arid planet is covered with sodium-rich deserts, deep rocky canyons, and endless dunes.

Coruscant (Star Wars)


Tatooine is famous in Star Wars for being a planet with two suns on which young Anakin Skywalker was a young boy.

Located at the edge of the galaxy, Tatooine is a nexus of hyperspace shipping routes, making the planet’s spaceport Mos Eisley a way station for traders. Far from the watchful eyes of the Empire, Tatooine also serves as a haven for frontiersmen such as smugglers, mercenaries, and bounty hunters, as well as the crime lord Jabba the Hutt. Only a few small human settlements and moisture farming communities (such as Anchorhead and Bestine) dot the barren surface of the planet. The deep deserts and wastelands are left to the native Jawas, the nomadic Sand People, and the strange life forms inhabiting remote areas.

Each day is 23 hours long, and the year has 304 days. In Tatooine, "First Dawn" refers to the time period between when the first and second suns rise. "First Twilight" is the time period between when the first and second suns set.


Anakin on Tatooine.

Mistakes on film: One shadow, but there are two suns.

Tatooine is the primary planet in the Tatoo system, this desert world is located in the Arkanis Sector of the Outer Rim Territories near Piroket and Ryloth. It is close enough to a major hyperspace nexus to make it easy to get to such worlds as Coruscant and Corellia, but its environment makes it one of the most inhosptiable places in the galaxy. The planet’s twin suns mercilessly heat the planet, keeping the sodium-rich deserts alive. The planet has a single, natural satellite.

Several decades before the Battle of Yavin, settlers arrived to colonize this first world in what was then called the J11.9 system. They coined the name Tatooine from the Jawa name for the planet, Tah doo Een e. The settlers established strongholds on the planet, and many smugglers and criminals have set up operational bases in its wastelands. The settlers there are primarily moisture farmers, extracting what little water they can from the atmosphere for survival. Its location on the galactic fringes makes it a perfect base for smugglers, mercenaries, and bounty hunters. The planet, despite its hostile ecology, supports human life was well as the native races of Jawas, krayt dragons, and Tusken Raiders. The planet’s remote location appealed to Owen Lars and his wife Beru, and they lived there with Luke Skywalker for many years. Tatooine’s average day lasts 23 standard hours, and its year consumes 304 local days. Note that the Star Wars Journal: Anakin Skywalker claims Tatooine is located not only near several hyperspace routes, but also near other galaxies.

It is interesting to imagine some of the possibilities of a planet with two suns. Are both suns on the same orbit, but simply in different points of that orbit? Or are they on separate orbits that cross paths? What if the two orbits were perpendicular or parallel to each other? How do their orbits relate to Tatooine’s orbit? What would things look like on Tatooine if the two suns crossed, were at the same or opposite sides of Tatooine, or any other arrangement of the three planets you can imagine? What would the shadows on Tatooine look like? What about the length of day, night, or the seasons?

Standard time

The standard hour and year are marked by Coruscant’s local hour and year. A standard minute consists of 60 seconds; an hour consists of 60 minutes; a day consists of 24 hours. A standard week consists of 5 days; a month consists of seven weeks. A standard year is 368 days, including ten months, three fete weeks and three other holidays.

According to Rebellion, Coruscant is located in Sesswenna Sector. Coruscant Standard Time is the galactic standard time reference, and was used to indicate the current time on the planet Coruscant, no matter where a being was in the galaxy. Many planets provided two time measurements: local time and Coruscant Standard Time. The dating systems of the Galactic Republic and Galactic Empire are unknown.


Air buses, Imperial City in Coruscant

The vast population of Imperial City uses many means of transportation, including ocean-liner sized air buses which dock at dizzying heights above ground level.


The seat of galactic government for as long as records have existed, Coruscant is the jewel of the Core Worlds and the center of the known universe. Nearly all of the planet’s land is covered by an unending, multileveled megalopolis whose foundations were laid at the beginning of the Old Republic, more than a thousand generations ago.

Coruscant is located at galactic coordinates (0,0,0), this planet in the Core Worlds was home to the Old Republic. It was renamed Imperial Center by Emperor Palpatine. When the New Republic was born, the planet was renamed to Coruscant. It has two moons, and orbits a small white sun.

The planet’s entire landmass has been covered (over the thousands of generations spanning galactic history) by multiple levels of the buildings that make up Imperial City. This means that there is little land available for growing food, and no natural rivers or lakes to provide water. To solve the dilemma of feeding and watering millions of inhabitants, many of Coruscant’s architects build self-contained ecosystems into their buildings. Engineers have developed a series of huge pipes through which polar ice water is pumped to the cities. Nearly everything on the planet is recyclable, from clothing to packaging and machinery. It was the center of all the Old Republic’s activities, and helped describe Galactic Standard time.

The Imperial Senate was convened there. When Palpatine assumed control of the Senate and the rest of the government, he established that Coruscant would remain the center of his Empire. He began a massive work effort to shape Coruscant to his desires, including installing a large number of surveillance systems. Following the Battle of Endor, Mon Mothma moved the New Republic onto Coruscant and again re-established the center of the Republic there. This came after the planet was liberated from Ysanne Isard, and the New Republic overcame the threat of the Krytos virus. Unbeknownst to all, Isard’s infamous Lusankya prison facility was hidden in the Super-class Star Destroyer Lusankya, which was buried beneath Imperial City. Following the death of Grand Admiral Thrawn, the Imperial Inner Circle began attacking Coruscant in an effort to regain the center of the galaxy for the Empire. This attack was driven back just before the Emperor was reborn as a clone, but the damage to the planet’s resources was horrendous. Also, the immediate space surrounding the planet was littered with starship wreckage for many years to follow. Once the reborn Emperor was destroyed, the New Republic began cleaning up the planet to make it more presentable as the center of the galaxy.

Days & months

Most of Star Wars uses a five day week, and a ten month year. Following are the days and the months in the Tapani Sector, which correspond almost directly to the Coruscant local calendar. The Tapani Sector is an area of the Colonies region of the galaxy which is considered a respected part of the Core Worlds, due to its proximity and wealth.

Days of the week:
first dayAtunda
second dayKatunda
third daySatunda
fourth dayDatunda
fifth dayNatunda

Months of year:
first monthElona
second monthKelona
third monthSelona
fourth monthTelona
fifth monthNelona
sixth monthHelona
seventh monthMelona
eighth monthYelona
ninth monthRelona
tenth monthWelona

Various Star Wars holidays

Expansion Weeka holiday celebrated throughout Tapani Sector, Expansion Week comes just before the upper class Capital Season. It fell between the months of Selona and Telona. (LE, PGT)
Harvest Daya holiday celebrated in Tapani Sector, it was first observed by the original settlers of the sector. The exact origins of the holiday are have been lost over time, but it is believed that the settlers traditionally commemorated the time of harvesting their crops on this day. In modern times, it is simply a day off from work. Harvest Day fell between the months of Yelona and Relona on the Tapani local calendar.
Mofata Polneyi month or season. Platt Mallar reported that the Yevethan attack on Polneye took place on the 40th day of Mofat.
Month of Plentythis Weequay holy season honored the moon god Quay. Temples on the planet Sriluur which were dedicated to Quay had an open skylight in their roof which allowed Weequay priests to track the moon’s progress during this month.
Productivity Daythis Tapani Sector holiday fell between the months of Nelona and Helona.
Shelova Weekthis traditional Herglic holiday celebrates commerce and family, two things which are interrelated to the Herglic race. A prominent holiday in the Tapani Sector, Shelova Week is a time to exchange gifts, make new business alliances, discuss trade arrangements, and spend time with family members. As the human population of the sector began interacting with the Herglics, they too began celebrating the holiday, although many humans simply take vacation instead of also developing business partnetships. On the Tapani local calendar, Shelova Week fell between the months of Helona and Melona.
Tapani Daythis holiday, celebrated in Tapani Sector, was held annually just after the month of Kelona, and before the month of Selona.
Thulpinthis is the name of the summer growing season on the planet Draenell’s Point. It lasts about 14 standard months, making up about a fourth of the planet’s long year.
Winter Fetethis is a holiday observed in Tapani Sector, and originally marked the winter equinox on the planet Pelagon. The settlers there were the first to celebrate Winter Fete, and when they began settling other planets in the sector, the holiday went with them. Over time, the holiday was modified to coincide with Coruscant’s Fete Week. In the current Tapani local calendar, Winter Fete falls on the very last week of the year, following the month of Welona.

Months on other planets

Two other planets are Ithull (Stenness system), the homeworld of the Colossus Wasp and the Ithullan race. The Ithullans were wiped out by the Mandalorians. A year on the planet lasted 25 standard months. Also, Tiss'sharl, which is a mild planet is the homeworld of the Tiss'shar race. It is covered with perilous, humid jungles. The average year on Tiss'sharl lasts 11 standard months.