The phrase "astronomical year" is correct and usable in written English.
It can be used when discussing time periods in relation to astronomical phenomena, such as the time it takes for the Earth to complete one orbit around the Sun.
Example: "The astronomical year is approximately 365.25 days long, which is why we have a leap year every four years."
Alternatives: "solar year" or "orbital year".
The reason there are 366 days every four years instead of the standard 365 is to remain in sync with the true astronomical year.
Every four years, we need to add a day to try and keep the calendar year in step with the astronomical year.
Naturally, this makes it the social event of the astronomical year, and parties are always better when they have themes (this is why Halloween parties are so much more fun than New Year's).
But the Gregorian version, which, when averaged over 400 years produces 365.2425 days per calendar year -- a very close approximation of the actual astronomical year -- has been more or less accepted worldwide as the de-facto secular calendar for conducting business.
We used the meteorological year, starting at December 1st, which groups the 3 coldest weeks of the year into winter (in the northern hemisphere) and the warmest into summer, in contrast to the astronomical year (starting Dec 21st).
For a more detailed explanation, see the Wikipedia article entitled "Astronomical year numbering": http://en.wikipedia.org/wiki/Astronomical_year_numbering.org/wiki/Astronomical_year_numbering
In 2013, that number rose to over 30,000 and this fiscal year, we've already seen 47,000 youth cross into the United States, a number that threatens to topple the already astronomical fiscal year projection of 60,000 apprehensions before September 30 of this year.
That is especially true after Philadelphia could not sign defenseman Shea Weber away from the Nashville Predators, despite an astronomical 14-year offer that would have paid Weber $27 million in salaries and bonuses in 2012-13.
And the cost is astronomical — $98,000 a year, Barry said.
The project will accumulate 6 million gigabytes of astronomical data every year.
Ikeda, M. & Tada, R. A 70 million year astronomical time scale for the deep-sea bedded chert sequence (Inuyama, Japan): Implications for Triassic–Jurassic geochronology.
