Ally is an independent, nearly 13-year-old girl who has been homeschooled her entire life at a remote campsite in New England. She possesses a deep passion for astronomy, spending her nights operating telescopes and searching for an undiscovered comet. Content with her isolated life, she is devastated when she learns her parents plan to relocate the family to Chicago following a major solar eclipse.

Bree is a popular, style-conscious middle schooler who expects to become a wealthy supermodel in the near future. She highly values fashion and her status in her school's social hierarchy. When her parents receive a grant that requires the family to move to a remote campsite for three years, Bree views the relocation as a disaster for her career and social life.

Jack is a shy, overweight 13-year-old who struggles with low self-esteem and poor academic performance. Growing up in a chaotic household with a frequently remarrying mother, he isolates himself in fantasy worlds of his own creation. He reluctantly joins a scientific expedition to the Moon Shadow Campgrounds to avoid repeating his seventh-grade science class.

Kenny is Ally's younger brother. Like his sister, he has spent his life isolated at the campgrounds under the instruction of their scientist parents. He is an expert in bugs and frequently assists with electronic equipment and reading technical manuals.

Ally and Kenny's parents are dedicated scientists who have run the Moon Shadow Campgrounds for a decade. They created the camp to gather astronomical data without the interference of city light pollution. They plan to hand over the camp's operation to another family once the major eclipse passes.

Bree's parents are accomplished research physicists. They have recently received a major grant to study dark matter at the remote Moon Shadow Campgrounds. They expect their daughters to adapt quickly to the sudden, drastic change in lifestyle.

Bree's younger sister is part of the Holden family uprooted to the remote campsite. Unlike Bree, she adapts more readily to the move and eventually participates in the camp's activities with the other children.

Claire is Bree's best friend from the city. She acts as a follower to Bree, sharing her friend's intense interests in fashion, makeup, and maintaining popularity at their middle school.

Mr. Silver is Jack's seventh-grade science teacher. Rather than forcing Jack to fail, he recognizes the boy's creative mind and invites him to assist with a cutting-edge international astronomy experiment during the upcoming solar eclipse.

Ryan is a teenage boy who visits the Moon Shadow Campgrounds every summer with his grandparents. Recently focused on building muscle to try out for varsity football, his changing interests complicate his long-standing childhood friendship with Ally.

Pete is a six-year-old boy traveling with the large group of eclipse chasers. He has a severe peanut allergy and forms a trusting bond with Jack during their bus ride to the campsite.

Stella is an enthusiastic, elderly eclipse chaser who is traveling to witness her sixth solar eclipse. She acts as a gentle spiritual mentor to Jack, taking an immediate interest in his private sketchbook and encouraging him to engage with the world.

Stella's adult son acts as Mr. Silver's assistant for the student trip to the eclipse. He is described as surly and uncooperative, showing little interest in helping the kids with their scientific tasks.

Ryan's grandparents bring him to the campground every year. They are currently going through a divorce, a stressful family situation that weighs heavily on their grandson during his stay.

Jack's mother has remarried multiple times since her first husband left. She methodically cuts her ex-husband's face out of all family photographs, creating a tense emotional environment that causes Jack to retreat into his imagination.

Jack's biological father left the family when Jack was only four years old. Because his face has been cut out of all pictures, Jack does not know what he looks like, but he secretly keeps a stuffed bunny his father left behind.

Jack's older brother is a successful, highly active athlete. His status as a major jock makes Jack feel even more insecure about his own lack of coordination and pudgy physique.

An unnamed tourist from Egypt who has traveled extensively to the Moon Shadow Campgrounds specifically to view the rare solar eclipse. She interacts briefly with Bree, offering an international perspective on the astronomical event.