Auden was a little hard on Tennyson. "In youth," says Wystan Hugh, "Tennyson looked like a gypsy; in age he was like a dirty old monk. He had the finest ear, perhaps, of any English poet, and yet he was also undoubtedly the stupidest." What livelier introduction could there be to a stanza written by this Alfred when already great, but not quite yet a Lord?
Consider the following:
We sleep and wake and sleep, but all things move;
The Sun flies forward to his brother Sun;
The dark Earth follows, wheel'd in her ellipse, And human things return upon themselves,
Thro' all the circle of the golden year,
and then address this fundamental question: what means this Tennysonian "circle of the golden year"?
There are several "years" to choose from, depending on how accurate one wants to be. As a first approximation a year is 12 months, or perhaps 3651/4 days. But to be more precise, one might think in terms of a side- real year, , the length of time it takes the Earth to orbit the sun and return to a position it occupied a "year" before with reference the background stars. By this reckoning, a year lasts 365.25636 mean solar days.
But if you want a calendar of practical utility, as distinct from one that works "with reference the background stars", it seems wise to define a "year" more carefully: it could be the time that elapses between the start of a particular season in one year and that season's subsequent commencement in the next. This, however, leads to complications.
The Earth's axis is tilted at an angle of about 23.5 degrees to the plane of its orbit around the sun. This axis, moreover, precesses like that of a spinning top; the direction in which the North Pole points in the sky revolves in a complete circle every 25,800 years, with a consequence that at present the astronomical seasons start ever so slightly earlier every year. If, therefore, you were to choose, say, yesterday's autumnal equinox as a starting point, you would find in due course that a year was 365.24201 days long.
The matter is further complicated by the fact that year length varies again depending on the chosen milestone in the cycle. Starting from the summer solstice, for example, the current year would be 365.24237 days in length; the vernal equinox gives 365.24219, and the December solstice 365.24274. In practice, the vernal equinox is our chosen reference point, and the tropical year, , on which our calendar is based, has a length of 365.24219 mean solar days.