Easy methods to inform time on Mars

by Alex Innanen

One in every of my favorite issues to examine are completely different calendars and strategies of timekeeping. Right here on Earth, there are all kinds of various calendars – the Gregorian, which you’re seemingly conversant in, the Julian calendar, and varied lunar, photo voltaic or mixture calendars. We additionally hold time inside a single day in numerous methods – the usual now could be a 24-hour clock, however at varied occasions folks have tried to introduce decimal time, the place every day may need ten hours divided into 100 minutes. And that is simply on our personal planet, the place typically the obvious motion of the solar and moon within the sky can provide you a way of when issues are occurring.

Unsurprisingly, while you transfer to completely different planets issues begin to get extra difficult.

Let’s take Mars as an example. Mars’ day (known as a sol) is about 40 minutes longer than an earth day. If you wish to use a 24 hour clock you both must have a sneaky not-quite-an-hour-long twenty fifth hour, or it’s a must to make each hour a bit longer. Which is what the Mars clock that’s used for mission planning does. However wait, does that imply every hour has greater than 60 minutes? Properly, probably not, in case you make every minute a bit longer than an earth minute, and you are able to do that, not by including additional seconds, however by making every ‘Mars second’ a bit longer than an Earth second. This fashion you’ll be able to nonetheless use a well-known 24 hour clock.

This doesn’t imply that there’s some intrinsic ‘Martian second’ that’s longer than an Earth second. Whereas the second is an SI unit, it’s pretty arbitrary, as is splitting up a day into 24 hours. It’s simply what we’re used to a second being.

One factor about spherical planets is that native midday – when the solar is straight overhead – occurs at completely different occasions in other places. That is the rationale that folks on Earth invented time zones, in order that native midday may line up – roughly – with midday on the clock. In actuality, there’s a good quantity of variation even inside a time zone. For instance, there’s a few 20 minute of distinction between native midday in Toronto and Montreal simply due to their distinction in longitude, despite the fact that they use the identical time zone.

There are not any official time zones on Mars and missions have a tendency to make use of native imply photo voltaic time (LMST), which is predicated on the typical­ size of the sol, break up into 24 hours. (There’s additionally native true photo voltaic time [LTST], which is referenced across the native midday, however drifts from 12:00 LMST all year long.) There’s a typically accepted time normal for Mars, known as Ethereal Imply Time (AMT) or Coordinated Mars Time (MTC) (akin to Earth’s Greenwich Imply Time (GMT)/Coordinated Common Time (UTC)) which check with the imply photo voltaic time at Mars’ prime meridian, the crater Ethereal-1.

The opposite factor about Mars is its yr is nearly twice so long as an Earth yr, about 668 sols or 687 Earth days. There may be some familiarity, although, as a result of Mars, like earth, has seasons! However Mars’ orbit is extra eccentric than earth’s – that’s to say, the trail it travels across the solar is barely extra rectangular. Earth additionally travels in an ellipse, and we do see the results of not orbiting in an ideal circle on Earth seasons – the northern summer season is about 94 days lengthy, whereas the northern winter is simply round 89 days – however to not so nice an extent as on Mars. There the northern spring is 194 sols whereas the northern autumn is simply 142 sols, a distinction of 52 sols.

So what if we wish to know what time of yr it’s? We are able to really use the place of Mars (or any planet) in its orbit to inform this – particularly a parameter known as photo voltaic longitude, shortened as Ls. We are able to begin the yr at a Ls of 0 levels, the northern vernal equinox (the beginning of northern spring). Every subsequent season then begins at intervals of 90 levels for a full 360 diploma orbit. This conference is utilized in most scientific contexts as a result of it will probably pretty simply inform you if occasions are occurring at across the similar time yr after yr. It additionally avoids having to cope with issues like leap years or leap seconds, as a result of Mars’ orbit will at all times be 360 levels – that’s simply how geometry works.

All of that is what’s used presently to orient ourselves in time on Mars, however there have additionally been quite a lot of makes an attempt to create calendars and timekeeping techniques that could possibly be utilized by folks dwelling on Mars itself by everybody from scientists to fiction writers. The calendars divide the Martian yr into months – which range of their size, and in what number of months there are in a yr – and weeks – once more, various in size and amount. Some calendars use acquainted names for months and days of the week, and a few make up new names, or new variations of the earth names. Stepping into all of them would in all probability take an entire sequence of blogposts, however it’s a very enjoyable rabbit gap to vanish down.