There's other religious calendars in use. None of them (including the secular "metric" ones) make much sense without further context. You want to measure the

There's other religious calendars in use. None of them (including the secular "metric" ones) make much sense without further context. You want to measure the seasons for planting? that's not the same thing as "where are we in the annual orbit", but there's a relationship. cf "easter". see also why land speed is measured differently than speed on water or in air. Though it looks, superficially, like you're measuring the same quantity, its actually more complicated than that. Finally, when the aliens land and we compare calendars, the biggest surprise will be the holiday celebrating Emperor Norton, which appears on all the greater Galactic event lists but is barely remembered here on his home world.