One Time for Every World - How I keep time across Earth and Mars, and the date I'm counting down to
If you've seen "Today is CSD ..." at the top of my posts and wondered what the number means, this is the guide. It's my own timekeeping system, Coordinated Stardate, or CSD. Here is how it took shape, in the order it happened.
What CSD is
The idea is simple. One number for a moment in time, and it's the same number wherever you are. Auckland, London, Texas or Arcadia Planitia, everyone reads the same figure.
It started out as just "Stardate". That name had a problem, because people hear it and think of Star Trek. TNG stardates were a writing tool, not a clock. Five digits, a season code, a decimal that means "sometime today, roughly." You can't take 41153.7 and get a real minute back out of it. So at the end of August (on CSD 3439.0622) I gave mine a proper name: Coordinated Stardate.
The word "Coordinated" is there on purpose, on the pattern of UTC and MTC. CSD is a single count from a fixed epoch, with no time zones. Earth UTC and Mars MTC sit under it as local views, not competing clocks.
Someone asked me a fair question: light takes minutes to travel between Earth and Mars, so how can one number mean the same moment on both? Pulsar Ticks handle it. A pulsar spins at the same rate wherever you see it from, so each observer just corrects for the light-travel delay from where they sit relative to the Solar System barycenter. Those are the standard Roemer, Shapiro and Einstein corrections pulsar timing already uses. That gives a shared coordinate time that works across the solar system, the same way GPS works. True simultaneity is still relative, but with those corrections CSD works as one number everywhere.
Why one number helps
Time zones are where plans go wrong. Someone says 7:15 CT and half the people reading it have to stop and work out what that means for them. A CSD skips that step. Set a time to call or catch up with someone, from anywhere on Earth or out of this world, and nobody gets the timezone wrong.
I use it for launch targets too. When Starship Flight 14 slipped to 28 September, 2026 at 07:15 CT, I posted the new target as Coordinated Stardate 3443.1135, with a link that opens it in your own local time.
It's also why my Flashbacks open with "Today is CSD ...". Anyone reading, anywhere, sees the same date stamp.
The CSD site
I built a small site for it with Grok Build: stardate.grok.me
Here's what it does:
- Shows the live Coordinated Stardate.
- Converts any date to a CSD, or a CSD back to a date, in your local time.
- Lets you add a CSD to your calendar.
- Has a simple REST style interface, so apps and tools like n8n can call it.
- Copies the number when you click it, with a small "Copied" notice showing it's ready to paste anywhere.
You can also link straight to a moment. The Flight 14 target, for example, is stardate.grok.me/?stardate=3443.1135, and it opens in the reader's own time.
The Mars clock
A day after the site went up, I added the time on Mars to the same page. A CSD doesn't care which planet you're on, so the Earth and Mars clocks can sit together on one page under the same number.
Local sol, HMS and CSD
Mars needs more than a shared clock. People living there will need their own calendar too. A Mars day (sol) is about 24 hours 39.5 minutes, and the scientific Mars Sol Date (MSD) is a running count of sols that began on 29 December 1873. That unbroken 150-year timeline is great for lining up telescope, Viking and rover records, but "Welcome to MSD 58,xxx" is an odd way to greet the first human residents of another world.
So in September I suggested keeping MSD for science and starting a parallel human-era count called HMS, Human Mars Sol:
- HMS uses years and sols, with no months.
- HMS 1.1 is the sol on which the first humans achieve a safe landing on Mars (touchdown with a viable habitat or vehicle, whether or not anyone steps outside that sol).
- Each new year begins on the anniversary of that landing sol, about every 668 or 669 sols, and time of day stays in MTC on a 24-hour clock (for example, HMS 1.1 10:00:00 MTC).
- Settlements still run on local solar time for daily life, the way astronomers use Julian Dates while the rest of us use the Gregorian calendar.
When someone asked me how time should work on Mars, I tried to fit all three layers into one reply. It came down to one line: local sol for daily life, HMS for the human era, CSD for anything across worlds.
My call: 21 November 2033
All of this comes together in one date. In September I called it: the first human landing on Mars, 21 November 2033, 01:00 UTC. That's CSD 3819.0300.
The reasoning comes from my Mars Independence series. Uncrewed proof first, then androids, then people. The 2030-31 window is for the androids, 27 000 Optimus ahead of any human. People ride the next wave, leaving Earth in early 2033 and landing in November at Arcadia Planitia, once pads, power and propellant already exist. The time of day matters too. On the ground that's Sunday 20 November at 8:00 pm Eastern (5:00 pm Pacific) in America and Monday 21 November at 2:00 pm in New Zealand, so both places can watch it live.
I also listed what would make me pull the pin: a failed or skipped 2028 cargo window, no working orbital refuel, a heat shield that can't take a Mars pulse even once, or Optimus production that never leaves the factory floor. Any one of those and 2033 becomes 2035.
Two days later the call still stood, and the countdown went live on the site.
Where to find it
The CSD entry, along with HMS, sits in my Space Lexicon, which I keep updating as new words come up.
The live clock, the converter and the landing countdown are all at stardate.grok.me. The landing countdown is at stardate.grok.me/?event=landing. Next time you set a call with someone in another time zone, try sending them a CSD instead.