Twelve years ago, Marian Halperin of Vineyard Haven began reading and copying the private journal of someone she didn’t know. Then she read and copied the letters he wrote far from home and the account book his father kept on the Island while he was away. Now it’s all in a book — Your Affectionate Son, Charlie Mac: Civil War Diaries and Letters by a Soldier from Martha’s Vineyard — and as of Thursday afternoon, you’ll have the chance to meet a man whose life is the most extensively, personally, variously and creatively chronicled of any Islander we know of from the 19th century.

As a bonus, you’ll also get to meet the woman who’s introducing him to us.

At 5 p.m. Thursday, the Martha’s Vineyard Museum in Edgartown celebrates the publication of the wartime journals and letters of Charles Macreading Vincent, a wry, red-headed fellow from Edgartown who enlisted in a Massachusetts regiment in the late summer of 1862, when things were going badly for the Union forces, and mustered out a second lieutenant after being among the first company of Northern soldiers to enter Richmond in the spring of 1865. From the pages of his three journals and 60 letters home, you’ll discover a kid whose ability to write clean, confident, evocative prose at the age of 18 startles even today, but whose character after three years of warfare reveals itself to be more reserved, sardonic and open to doubtfulness than he might wish us to know.

In the summer of 1997, as Mrs. Halperin finished transcribing the Charlie Mac diaries at the museum, she said: “I think he’s trying hard to be one of the boys; that’s one of the things that’s interesting to think about. I’m not sure he really was one of the boys, and yet we get the sense that he feels very often as a private that he ought to try to be one.” Having finished the transcription and annotation of the full collection, and readying herself at the age of 84 to see her first book published this week — Mrs. Halperin will speak at the celebration at the museum on Thursday — she added a new thought about the sort of man he might have been: “I think he did an awful lot of bolstering himself [through] his patriotic writings. Do you feel that way? When he gets frightened, he writes about it, and then [tries to convince himself] it’s all worth it.”

Charlie Mac — the playful nickname he uses for himself — was born in Edgartown in 1843 to Samuel Gifford and Harriet Pease Vincent; both family names were among the most prominent in the civic, commercial and religious life of the Island. He apprenticed as a printer at the Vineyard Gazette and would serve as the third editor of the paper for five years, beginning in 1867 at the age of 24. He went on to edit several mainland sheets before he was appointed assistant managing editor of the Boston Globe, where he created Table Talk, a laconic column of gossip and observations of life around him. His first wife Sarah Smith Vincent died in 1878 after bearing four children, and he himself would die of diphtheria in January 1881, aged 37 and only eight weeks after marrying his second wife Mary Z. Roberts.

Mrs. Halperin, a former director of what is now the Martha’s Vineyard Museum, first came to the Island with her late husband Samuel in 1964. She has lived year-round near the Lagoon since 1971. After she completed the transcription of the Charlie Mac diaries and letters in 1997, she began to consider publishing them as a book to benefit the museum. But this meant taking on a vast new task, which occupied her on and off for the past 10 years: “I realized that a great many of the things that Charlie Mac mentions needed a little explanation: who was this person, what was the relationship and so forth.” As Mrs. Halperin began to annotate the journals and letters — including contextual information about nearby battles and concurrent events on the Vineyard — John Walter of the publishing company Vineyard Stories took on the assignment of editor and project director. “He turned out to be a Civil War buff, very enthusiastic,” she said. Nis Kildegaard, a freelance editor and former news editor of the Gazette, compiled a lengthy, useful index.

So what portrait of Charlie Mac emerges from his own hand? What do the parallax views from private diaries and letters home tell us of a youngster who came fully to manhood during a time of horrifying internal rebellion?

Well, the letters — especially the early ones — are often filled with boyish nonsense, including invented language, florid descriptions of affection for parents and siblings and demands for clothing and food (including a stuffed chicken, which is sent by mail and which he actually eats). His journals, though occasionally saucy about commanding officers (“Col. Burr Porter. . . has resigned. . . . [He] has been fairly bewitched all winter to get off to the front, where he was in hopes to get into a fight so that he could kill off a lot of his men and get a Brigadier General’s commission”), are more often written like newspaper accounts; they sometimes address an imagined reader or “you in the North” and rarely reveal anything visceral about the pretty girls he sometimes sees in a town or the fear he feels during a night of picket duty near the enemy. Throughout the diaries, there’s a sheen of official reportage, and of pride in the language he’s choosing, that keeps you reading Charlie Mac without quite knowing him.

For all his gifts as a journalist, Vincent is a man who writes without irony in one entry of a land “that has been and is still polluted by the curse of African Slavery” and casually uses epithets in the next. He tries — unsuccessfully — to get a commission as an officer in a Negro regiment, feeling that blacks fight hard and that it’s a road to personal advancement, but with fellow soldiers he blithely disassembles shanties, possibly still inhabited by black families, so that they can reinforce their own tents. In this, he is a man of his time, but Mrs. Halperin could never quite get away from the language he used and the conflicted views he held: “His attitude toward the blacks he meets makes you uncomfortable. I know it was common into my day, certainly. But it’s hard to justify his theoretical attitude in his comments. But his father was in a minstrel show on the Vineyard during the Civil War. Right in Edgartown! Lord!”

Still, there are moments when the reporting is sensational. He gives an account of a forced divisional assembly to witness the execution of a deserter (Accompanied by a dead march, “the doomed man walked with a firm step to his grave, the coffin was taken out and placed beside his grave. He took his seat upon the coffin. . . .”). And he writes of another man, who seems to have been old enough to recall the presidency of George Washington if not the Revolutionary War, and who stood by the tracks with his family and “broke down in tears, placing his hand on his heart, and then raised his hands clasped above his head, no doubt invoking God’s blessings upon us” as Charlie Mac and a trainload of his comrades in arms rolled by the ancient’s home in the loyalist Maryland countryside.

He is an educated man, his handwriting beautiful, the title page to the second journal showily inscribed Liber Segundus. That someone high up in the ranks catches the look of intelligence in his freckled face and makes him a quartermaster sergeant, responsible for writing dispatches, keeping accounts and looking after baggage, is no surprise. Charlie Mac can keep pace on successive 18-mile marches between Virginia encampments, but he’s a pragmatist too: When he contracts typhus and loses a third of the weight on his slender 145-pound frame in the first early winter of his enlistment, he’s quick to call for an uncle, Richard L. Pease of Edgartown (a great diarist in his own right), to come see if he can get him a furlough. Uncle Richard arrives, tries — and fails. In the fall of 1863, a year into his service, Charlie Mac can still report not a man lost in his own company, but at that moment, as the epidemic boils along, only 300 men out of the 850 in his regiment fit for duty.

The diaries end on May 20, 1864, four days after Rebel forces begin a series of attacks, killing 17 men in his own company and nearly 100 in the whole regiment at Drury’s Bluff in Virginia. He learns of wounded men left on the field to die, lists amputations and describes burying a young soldier by the side of a road and personally leaving behind “a rude headboard to his grave to mark his resting place.” Though he keeps writing letters home until his discharge in June, expressing gratitude that he was posted to the rear with the quartermaster’s property when the real fighting broke out, there are a few blank pages left at the end of Volume III. For a young man who filled up every inch of every diary he kept, those blank pages may say more than anything he might have written about what he was suddenly seeing and hearing in the field.

A party to celebrate the publication of Your Affectionate Son, Charlie Mac: Civil War Diaries and Letters by a Soldier from Martha’s Vineyard will be held Thursday at 5 p.m. on the grounds of the Martha’s Vineyard Museum at the corner of School and Cooke streets in Edgartown. Refreshments will be served.