Valentine's In Space

As far as romantic anniversaries go, I always liked the idea of celebrating prime-numbered months. One month is a bit soon to start celebrating, but thereafter you get quite frequent parties early in the relationship where a couple of months can make a difference to how serious it feels, then it tails off until they’re annual or less frequent, but still occasionally giving you two pretty close together. Instead, though, my girlfriend and I put the start of our relationship into nerdiversaries.com.

Nerdiversaries is a website built by Matt Parker. The idea is, you put your date and time of birth into the site, and it will spit out a calendar of alternative birthdays you may wish to celebrate: 69³ seconds, for example, or 333,333 minutes. I don’t think it was meant for romantic anniversaries, but there’s nothing much he can do to stop us using it that way.

According to the website, Monday would be our one-year anniversary if we lived on Venus. A Mercurian year is shorter still (around 88 days), and the next one is an Earth year with which I assume you’re familiar. This should not be a surprise: we can use Newtonian mechanics to derive an equation for the orbital period T of a body given the mass of, and distance from, the sun (M and r respectively). It’s called Kepler’s Third Law, and it comes out at:

T² = 4π²r³ ÷ GM where G is the gravitational constant.

Anyway, the point is that if the length of your relationship so far is T, this equation gives you the distance at which you would have to orbit the sun for today to be your first anniversary:

r = 1.819 × ∛T² where r is measured in millions of miles, and T in days

You can now think of your first anniversary as a spacecraft, which set out from the sun the day you got together. When you had been together for one year, it passed Earth. It passes Mars after 687 days, Jupiter after 12 years, and Uranus 72 years after that.

The furthest any man-made object has ever travelled from Earth is 119AU — this is Voyager I, but you would have to stay together for rather more than a millennium to pass that. It seems that the solar system is a practical limit on anniversaries, as well as spacecraft, but it’s not just romance we should celebrate, and the first anniversary of any event before November 713AD is further out than Voyager I.

To be honest, though, I quite like that your first anniversary will approach the edge of the solar system almost asymptotically. It’s a pretty way of visualising how well you’ve done.