The Structure Of Star Of The Sea

Poul Anderson, Time Patrol (New York, 2006), pp. 467-640.

Large Roman numeral, I: mythological writing.
Small Arabic numerals, 1-10: the narrative.
Large Roman numeral, II: mythological writing.
Small Arabic numerals, 11-19, the narrative continued.
Large Roman numeral, III: legendary writing.
Small Arabic numeral, 20: the narrative concluded.
Large Roman numeral, IV: a Marian prayer.

I and II are imaginative reconstructions of earlier stages of Northern European mythology. In I, the sea goddess, Niaerdh, marries the agricultural god, Frae.

"'I will come to you on the rainbow,' Niaerdh plighted.
"So it was. So it is." (p. 469)

In II, they are Naerdha and Froh; and other gods and beings are involved.

Both mythological accounts explain why the divine couple are apart every winter but rejoined in spring.

In III, a hunter interacts with the sea goddess, Nehalennia, and becomes a sea trader.  

IV is a seafarers' prayer to Mary, named "Star of the Sea" after the goddess.

In later installments of the Time Patrol series, dates are used as section headings. This practice is observed for some chapters of "Star Of The Sea":
 
10    A.D. 60.
11    A.D. 49.
12    A.D. 43.
14    A.D. 43.
15    A.D. 70.

Two Patrol agents follow a trail back through time, then return to apply the knowledge they have gained.

Some chapters begin with indications of time or season:

2   "In the closing decades of the twentieth century..." (p. 477)
3   "Winter brought rain..." (p. 494)
5   "Wind rushed bitter..." (p. 518)
7   "Suddenly springtime billowed over the land." (p. 530)
9   "The months toiled on..." (p. 543)
15    "The sun was newly down..." (p. 15)
16    "Sleet hissed..." (p. 601)
17    "The early sunset smoldered..." (p. 610)
19    "New-fallen snow..." (p. 622)

Of these, 2 expresses the viewpoint of a Time Patrolman not yet embarked on a mission whereas the others reflect "...the mysteries of day and night, summer and winter..." which "...pervaded...the souls of the folk." (p. 539)