fictional moons

Fortnigh and Sevnigh

(česky: Týden a Čtrnáctdní)

Let us imagine a world, where the Earth has beside the Moon two more, in a 1 : 2 : 4 resonance, similarly to Jupiter's moons.

If our Moon has a orbital period of one month, then the name of the middle month will be Fortnigh and the inner Sevnigh.

In the Germanic languages, the name of the orbital period is not the same as the name of the month, but is derived from it by the suffix -t (after Grimm's law -þ): English Moon → month . Because the word fortnight (← forteen nights) also ends on the sound t (night ← PIE. nekʷt-), we can create a name Fortnigh by analogy by tearing it off. We have no such luck with the word week and as a solution I see replacing it with a neologism sevnight (← seven nights) and name the inner moon Sevnigh.

The sidereal periods of these moins will be half and a quarter of the sidereal period of the Moon, synodic periods are obtained by subtracting the frequency of the annual circulation from the frequency of the monthly circulation. The exact length of the year and month varies, for the current time, rounded values of 365.2422 and 29.5306 days are usually used. We will use the value 365.2421875 (= 365 + 1/4 - 1/128) for the length of the year .

These values were calculated as follows:

<script>
year = 365.25 - 1/128;
month = 29.5306;
sid_month = 1 / (1 / month + 1 / year) 
sid_fortnight = sid_month / 2; 
sid_sevnight = sid_month / 4; 
fortnight = 1 / (1 / sid_fortnight - 1 / year) 
sevnight = 1 / (1 / sid_sevnight - 1 / year) 
document.write(year
 + "<br/>\n" + sid_month
 + " " + sid_fortnight
 + " " + sid_sevnight
 + "<br/>\n" + month
 + " " + fortnight
 + " " + sevnight
 );
</script>

which gives:
365.2421875
27.321591770525725 13.660795885262862 6.830397942631431
29.5306 14.191590030429994 6.960567589428822

other fictional moons