Prohowich Martian Calendar
The complete Mars calendar, MY −0199 to MY 1500: built for accuracy, not fiction.
Prohowich Martian Calendar converts any Earth date to its precise Mars equivalent using the Mars Solar Date (MSD) system: no guessing, no approximation.
What It Does
- Shows the current Mars date, time (AMT: Airy Mean Time), and sol count in real time
- Browse any Mars Year from MY −0199 to MY 1500
- 24-month Martian calendar with fixed month lengths per century, recalculated each century to account for Mars orbital precession
- Season tracking: Northern and Southern hemisphere views
- Lₛ×15° milestone table: every orbital checkpoint with AMT time
- Full year view with orbital events: equinoxes, solstices, Aphelion, Perihelion
- Earth↔Mars time converter
- Complete Mars Year table with MNYD, MSD, sol counts, and all seasonal markers
- Three day-of-week naming systems: Earth, Numerical (Greek ordinals), Mars Planetary
- Home-screen widget: Earth UTC and Mars AMT side by side, tap to cycle notation
- Full-screen screensaver: a live Mars clock, calendar and sky
- Runs on phones, tablets and Android TV, driveable entirely by remote
The Screensaver
A full-screen live view: the Mars clock, the current month’s calendar, and a Martian sky rendered from the real solar geometry at Airy Crater. Sunrise, sunset, the blue glow around the setting sun that Mars actually has, and a star field projected from a real catalog in Mars’s own rotating frame. Phobos and Deimos cross it at their own periods; Phobos rises in the west, because it laps the planet.
A speed control drives time forward or back across the whole MY −0199 to MY 1500 range on a continuous logarithmic scale, from real time up to three million times faster, a Martian month every second, and stops cleanly at either end of the table rather than running off it. On a television the remote’s own transport keys drive it: Play and Pause stop and resume the clock, Rewind and Fast Forward step the speed, and Now returns you to live.
Browse to any date in the app and the screensaver opens there. It also takes a
date on its own address, so a link can land on a moment:
?my=39&mo=1&sol=1 opens on the first sol of Mars Year 39,
which began 2026-09-30T05:59:21 UTC.
The Ephemeris
Solar longitude, Lₛ, is what actually defines where the months fall. It is computed from JPL DE441, the ephemeris the planetary community uses, rather than from a published series approximation.
It is fitted as four 800-year blocks against the Mars barycenter and the IAU 2000/2009 Mars pole, to 1.2 × 10⁻³ degrees RMS. Every one of the 40,800 Lₛ×15° crossings was verified to fall inside its correct month. The app, the home-screen widget and the screensaver all evaluate the same generated series instead of separate transcriptions of it.
Where the Year Starts
A Mars year begins at the northward equinox, solar longitude Lₛ = 0°. This calendar dates each year from the 00:00:00 AMT immediately preceding that crossing, so a year always starts on a sol boundary.
The convention is NASA’s: its Planetary Data System dictionary states that the year number “is incremented by 1 for each Martian spring equinox (solar longitude 0 degrees)”, with Mars Year 1 beginning on April 11, 1955. This calendar uses the same epoch, and its Mars Year 0 begins 24 May 1953, matching Piqueux et al. (2015), the paper that extended the numbering backwards and gave the negative years this app covers.
Accessibility
- Every interactive control meets the 44 px touch-target minimum
- Text contrast is above 4.5:1 throughout
- The whole app is reachable by keyboard, D-pad or TV remote, with no touch required
- Press ? for every key, button and D-pad control in one list
- The screensaver’s sky is damped at high playback speeds so it cannot flash more than three times a second, the WCAG 2.3.1 limit for photosensitive seizure risk
Date Notation
A Mars date joins to a Mars time with M, an Earth date to an Earth time with T:
MY0039-01-01M00:22:37 AMT
2026-09-30T06:22:36 UTC
T is doing double duty: it is ISO 8601’s date-time separator, and it is Terra.
M is not invented either. NASA’s Mars Science Laboratory flight products write
timestamps as Sol-00307M13:02:09.505, and that M is the only
Mars-time marker in real operational use. Below a sol there is no accepted
abbreviation for a Mars hour, minute or second anywhere, so this calendar
invents none: durations are given in sols, which state fractionally.
The app writes any date at ten levels of detail, L0 to L9, from
39Α01#5 to the full astronomical form. Tap the date under the
clock to cycle them.
The Printable Sheets
Alongside the app, each published Mars year is rendered offline as an 11×17 sheet: all 24 months in a single spread, the Lₛ×15° milestones with their AMT times, the ephemeris block for the year, and on the second page every sol of that year with its month, Lₛ and sol start in UTC.
They are generated by a separate tool reading the same DE441 series the app does, so the same data is laid out twice by two different renderers. Each sheet names the build it came from. They are produced for the project’s own use and are not distributed with the app.
The Calendar System
Month lengths are fixed within each Martian Century (~100 Mars years, ~188 Earth years), then recalculated for the next century using actual Lₛ crossing times. Regular years = 668 sols; augmented (leap) years = 669 sols, with the extra sol added to Month 24.
The Icon
38χ marks when the app became viable: Mars Year 0038, Month 22 (Χ: Charmē). The background is Mars. The ring shows all 24 months by season color, sized by sols per month.
Privacy
Does the app collect any personal data?
No. There are no ads, no accounts, no analytics and no data collected, and the app makes no network requests. It saves your day-of-week name system and hemisphere view to your device; if you add the home-screen widget, it also saves whether that widget is expanded and which notation level you last chose. None of it leaves your device. See the full Privacy Policy.
No ads. No accounts. No data collected. Nothing leaves your device. See the full Privacy Policy.
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