"tropical year" is a correct and usable phrase in written English.
It is defined as the period of time it takes for the Sun to return to the same position relative to the stars in the sky, which is about 365.24 days. For example, "By observing the cycles of the seasons, the ancient Babylonians were able to calculate the length of a tropical year."
The tropical year and the synodic month are incommensurable, 12 synodic months amounting to 354.36706 days, almost 11 days shorter than the tropical year.
Such heliacal risings could, therefore, be used to determine the seasons and the tropical year.
And the solar calendar presented an even more fundamental problem that of finding the precise length of the tropical year.
The most significant of all the early attempts to provide some commensurability between a religious lunar calendar and the tropical year was the Metonic cycle.
An unwitting approximation to the tropical year may also be obtained by intercalation, using a simple lunar calendar and observations of animal behaviour.
Calendrically, it was an important discovery because the tropical year is measured with reference to the equinoxes, and precession reduced the value accepted by Callippus.
Climate: Tropical year-round, ranging from 21C to 32C.
Thus the Callippic cycle fitted 940 lunar months precisely to 76 tropical years of 365.25 days.
The error with respect to the 365-day year and the heliacal risings of Sirius amounted to one day every four tropical years, or one whole Egyptian calendar year every 1,460 tropical years (4 × 365), which was equivalent to 1,461 Egyptian calendar years.
But the greatest advantage of this cycle was that it laid down a lunar calendar that possessed a definite rule for inserting intercalary months and kept in step with a cycle of the tropical years.
But what's perhaps most satisfying about recreational snorkeling is that its joys are the same for those who do it on vacation once every few years as for those who live in tropical locales year round.
