Read Online The Movement of Stars by Amy Brill - Free Book Online
Authors: Amy Brill
Tags: Historical
Ads: Link
immodest, for one. And vain. Worse, thinking about her body led to the desire to touch, and the few times that Hannah had ventured in that direction, in the dark under her quilt, she’d been too ashamed to even enjoy the sensation. An ailing elder cousin had once confided on her deathbed that she was grateful her husband had never seen her naked, and Hannah, at fourteen years of age, had felt that she understood her completely, and been thankful on her behalf.
In the east, Arcturus was already high. Hannah surveyed the sky as if she could see clear through the visible horizon in the distance and all the way to the planets Dr. John Herschel, the great cataloguer of the skies, saw through the lens of his twenty-inch refractor, to Ceres and Pallas, and beyond. She set down her stool and began to speak, her voice sliding smoothly across the rooftop.
“Imagine that you are standing on the very surface of the Earth,” she said. “Imagine there are neither trees, nor houses, nor mountains— aught but you, balanced on a marble that is floating in the Heavens. Of course, you’re spinning with this marble, and also moving in a great arc about the sun, completing one circle each 365 days.
“Now imagine that you’re holding an enormous parasol, the tip of w h i c h e n d s a t P o l a r i s — t h e r e . ” Hannah pointed at the North Star. “The circumpolar stars—those closest to Polaris—you may imagine as fixed upon the inside of the parasol. They rotate around the Pole Star but maintain their relative distance to each other. We can always see them. The rest of the celestial bodies rise and set as the Earth turns, seen only at certain times or in certain seasons.
“In addition, if you draw in your mind a series of lines parallel to the equator, circling the inside of your parasol at equal distances from the north celestial pole and each other, forming a series of concentric rings, you’ll have a picture of the lines we use to measure the distances of stars from the celestial Equator.”
“They are the lines of latitude?” Isaac asked, his eyes trained on Polaris.
“Yes, as projected onto the celestial sphere. We call them the parallels of declination. Another set of such lines—the hour lines— corresponds to the lines of longitude. They encircle our Earth from the opposite direction, passing through the North and South Poles. We use these lines to measure the angle of a given star at a given time, relative to the horizon, so that we might deduce our location on the sphere by means of triangulation.”
Hannah glanced over at Isaac; his eyebrows veed together as if he was thoroughly perplexed.
“Think about it this way: the sun is our nearest star. It appears to travel across the sky each day, taking 24 hours to make a full circle of 360 degrees, or 15 degrees of longitude each hour. If we measure the sun’s exact position at noon, and we know the time at your home port, as well as the time at your location at sea, a comparison of the two will determine your longitude. Which is of course why you need the . . .”
She trailed off, hoping Isaac would finish the sentence, but he was silent. His eyes were closed.
She felt a flash of anger, chased by a pang of disappointment. Either he wasn’t paying attention or she was boring him to sleep. Hannah tilted her head to get a better look at his face. The tender veil of light from the crescent moon silvered his cheek and brow and outlined his mouth. His lips were full as a woman’s—not any women she knew, but those who frequented the taverns by the wharves. Slicked with paint and perfume. She wondered if his lips were soft, and then, shockingly, what they would taste of. Her skin tingled with gooseflesh and she shook her head, now glad his eyes were closed. She’d lost her place in the lesson. What had she been saying?
“The chronometer,” she snapped. “Do you understand?” Isaac sighed and shook his head slightly, then opened his eyes, keeping his gaze on the
In the east, Arcturus was already high. Hannah surveyed the sky as if she could see clear through the visible horizon in the distance and all the way to the planets Dr. John Herschel, the great cataloguer of the skies, saw through the lens of his twenty-inch refractor, to Ceres and Pallas, and beyond. She set down her stool and began to speak, her voice sliding smoothly across the rooftop.
“Imagine that you are standing on the very surface of the Earth,” she said. “Imagine there are neither trees, nor houses, nor mountains— aught but you, balanced on a marble that is floating in the Heavens. Of course, you’re spinning with this marble, and also moving in a great arc about the sun, completing one circle each 365 days.
“Now imagine that you’re holding an enormous parasol, the tip of w h i c h e n d s a t P o l a r i s — t h e r e . ” Hannah pointed at the North Star. “The circumpolar stars—those closest to Polaris—you may imagine as fixed upon the inside of the parasol. They rotate around the Pole Star but maintain their relative distance to each other. We can always see them. The rest of the celestial bodies rise and set as the Earth turns, seen only at certain times or in certain seasons.
“In addition, if you draw in your mind a series of lines parallel to the equator, circling the inside of your parasol at equal distances from the north celestial pole and each other, forming a series of concentric rings, you’ll have a picture of the lines we use to measure the distances of stars from the celestial Equator.”
“They are the lines of latitude?” Isaac asked, his eyes trained on Polaris.
“Yes, as projected onto the celestial sphere. We call them the parallels of declination. Another set of such lines—the hour lines— corresponds to the lines of longitude. They encircle our Earth from the opposite direction, passing through the North and South Poles. We use these lines to measure the angle of a given star at a given time, relative to the horizon, so that we might deduce our location on the sphere by means of triangulation.”
Hannah glanced over at Isaac; his eyebrows veed together as if he was thoroughly perplexed.
“Think about it this way: the sun is our nearest star. It appears to travel across the sky each day, taking 24 hours to make a full circle of 360 degrees, or 15 degrees of longitude each hour. If we measure the sun’s exact position at noon, and we know the time at your home port, as well as the time at your location at sea, a comparison of the two will determine your longitude. Which is of course why you need the . . .”
She trailed off, hoping Isaac would finish the sentence, but he was silent. His eyes were closed.
She felt a flash of anger, chased by a pang of disappointment. Either he wasn’t paying attention or she was boring him to sleep. Hannah tilted her head to get a better look at his face. The tender veil of light from the crescent moon silvered his cheek and brow and outlined his mouth. His lips were full as a woman’s—not any women she knew, but those who frequented the taverns by the wharves. Slicked with paint and perfume. She wondered if his lips were soft, and then, shockingly, what they would taste of. Her skin tingled with gooseflesh and she shook her head, now glad his eyes were closed. She’d lost her place in the lesson. What had she been saying?
“The chronometer,” she snapped. “Do you understand?” Isaac sighed and shook his head slightly, then opened his eyes, keeping his gaze on the
Similar Books
