From my bed, I watch the moon. My youngest sister crawls in with me. We curl together, spine against spine. And in its gentle light, she and I slumber amid moon-cast shadows. It seeps into our skin. It settles in our bones. We are pulled skyward and bathed, baptized, reborn. We belong to the moon and it is ours.

“Moon”—the word is an ancient one. The root is Proto-Germanic, maenon, meaning both moon and month. Mona, mano, maan, mena, mene: the words are strikingly similar across many old tongues. For several of these languages, Greek, Italian, Celtic, and Armenian, the word now only means month. Lunar cycles have been used throughout the course of human history for measurement. Women are considered the first scientists because they were hunter-gatherers, watching the world around them, and conducting the first studies in natural observation. They recognized the parallel between the cycles of female menstruation and the cycles of the moon. These two words share their origins. Waxing: light comes across, swelling from the right. Waning: darkness follows. Waxing, waning. Waning, waxing. The full moon, rich and round, gets eaten away in careful bites, the most meticulous of devourings.

Each lunar cycle begins with the new moon: it sounds so young, so fresh, and so bright. But on the night of the new moon, there is no moon at all—merely a darkness in the sky. The moon swells slowly, like the gestation of a child, characterized by that initial lack, the expectancy. At the apex of the lunar cycle comes the full moon. Swollen and heavy, it seems representative of all that is womanly and round.

***

I was almost thirteen when my parents decided they wanted another child. Before my youngest sister was born I had been one of three, a middle child, with a slightly older brother and a slightly younger sister. Curiously, it was through the birth of this final sister, this last little family member, that I grew up. She aged me.

My memory of the summer of my mother’s final pregnancy is characterized by my recollections of the day my father returned from Iraq. At first it’s only an image: my mother and father embracing outside the plane hangar at the military base. My father has returned and he makes it just in time. My mother is due any day. In my mind they’re backlit by the setting sun, silhouettes. I’m pretty sure it is actually high noon in this particular memory, but who can be upset by a little post-action dramatization?

So, they’re embracing: her arching, 5’4,” massively pregnant, up and over that swollen moon of a belly to embrace him, 6’2.” A slightly comical pairing, yet at the same time so imbued with my understanding of my parents and their relationship that it seemed to me almost tragic, even at that age. Like I said, he’s made it just in time. He left again soon after.

At this point, I was trying terribly hard not to cry. What an awful, grown-up, suffocated feeling. Restraint is definitely an adult concept. At that moment I felt like all that was young and weak and vulnerable about me was choked up in my throat, rising like vomit. Yet I decided to restrain myself, not to cry, and that choice stands as one of the few identifiable moments in my life where I know I grew up. In that choice, on that day, I got older.

***

The moon is unswerving in its devotion to Earth: our natural satellite. Rotating on its axis at approximately the same speed it revolves around the earth, we only ever see one half of the moon. Its dark side will never be revealed. It is 2,160 miles in diameter. 238,857 miles away. Yet it does not leave.

The moon is the second brightest object in our sky. Its surface is dark, yet reflective, like coal. Its core is solid: strong and iron-rich. Before my sister’s birth I went with my mother to one of her ultrasounds. They situated her on the table. It looked awful, clinically cold, clinically green. She hadn’t wanted to go alone. So there I was, standing by her side as they glopped the gel on her stomach. Somehow it was worse that it had no color. Oozy and thick, her flesh distorted through the colorless goop looked alien to me: shiny, melted out of shape, and wrong, like the bubbled flesh of a burn victim.

Suddenly feeling quite nauseous I went into the hallway, leaned against the wall, and slid down. The cheap wallpaper brush-burned my lower back. Curled at the base I ended up with my head between my knees, in fetal position— of all places. I thought of my mother’s strength and her brave iron core, carrying another child at thirty-nine while my father was so far away. I took a few deep breaths. Then I picked up my head and went back inside smiling.

***

The moon has often been associated with madness. People used to think that because the moon pulled tides, it pulled the fluids in the brain. The word “lunatic,” developed in the late thirteenth century, means: a person affected with periodic insanity dependent upon the changes of the moon. The origin is Old French, lunatique—meaning insane—and Latin, luna—meaning moon, or moon goddess.

I couldn’t sleep at all the night after she was born. I kept dreaming that I had her in the bed with me. And I would reach, reach both in my dream and in reality to the crook of my arm. I would reach to place a hand on her soft belly, to reassure myself that she was there, that she was alright. But of course she wasn’t there. She was at the hospital where she was supposed to be, no doubt snug and safe, all rolled up like a little piece of sushi, face poking out of that rice-white swaddling.

So my arm would thud to the mattress. And I would awake, panicked, searching her out. Blind in that dark bedroom, my eyes frantically roved the moon shadows until I realized, remembered, and fell to fitful sleeping once more—only to reach and thud, panic and remember. Again. And again. And again. Such frantic anxiety and fear for another, such a hyperactive sense of responsibility was crazy, insane. Yes, she aged me.

***

Once I was moon-gazing with my sister one summer evening. I held her cocooned in my lap and lazily we stared at the sky while the Adirondack chair pressed red lines into the undersides of my thighs. It was then that we noticed the darknesses, the spots on the moon. She thought them freckles like her own, dotting across the moon’s nose. Ancient scientists thought they were large bodies of water, moon-oceans and named them maria, which is Latin for seas. But both were wrong: the marks are neither freckles nor seas. No water in liquid state can exist on the moon. It becomes decomposed through a process called photodissociation and lost to space. Selenography, or the study of the physical features of the moon, has revealed that these dark patches are craters. Deep and wide, these chasms might have once held seas of some sort, so the ancient scientists weren’t far off. But I like my sister’s answer better.

The moon may not have water, yet it controls ours. It pulls the tides and lengthens the days. Tidal theory is one of the biggest messes in contemporary physics. The sun has a stronger gravitational effect on the Earth than the moon. Yet the tides are pulled by the moon. Tides pulled by the sun would be about 180 times as great. The solution to this riddle involves a lot of complicated math, numbers and letters lining up together to prove something, which, in layman’s terms boils down to a simple matter of cancellation. Apparently, the tidal forces result from imperfect mutual dissolution of centrifugal and gravitational forces at a specific distance away from the system’s center of gravity. I’ve always thought there was something almost sad about the tides. It’s an embrace, but it’s also an abandonment. Ebb, flow. Come, go.

My littlest sister has always loved the ocean. When she first saw it, she was still crawling. The moment her knees and hands touched sand, she headed for the water. That initial mouthful of brine did little more than momentarily stun her. Then she was crawling again, deeper into the waves. Laughing, I had to carry her shoreward repeatedly. If I hadn’t, she would have continued onward, never pausing, even as the sea closed over her head.

***

The tides tease in their reach and retreat. Constant yet every-changing, they can no more cease their fickle habits than a child can keep from growing. I understood this intuitively of course. My sister would grow older and need me less.

Pain is inherent in loving that which cannot remain the same. But the heart is slow to learn.

***

The moon has moonquakes. They’re weaker than earthquakes and are caused by a sudden release of built up tidal pressures. Since there is no water on the moon to mute the tremors, they last longer. The moon shudders. It quivers like a racing heart, trembling like adrenalized limbs.

One day a friend of mine came over to pick me up for practice. She had a cold and her already deep voice had deepened considerably. My sister had just begun stringing simple sentences together: subject and verb, occasionally in agreement.

“You sound like a man.” She said it without inflection, a child’s observation, unintended to harm and oblivious to the constraints finer social manners would soon teach her. My friend bent down till her eyes were level with my sister’s.

“Your hair looks like a man’s.” She threw out the retort, mocking the mop of chocolate curls that were just starting to come in on that soft-centered crown and hurt welled in my sister’s round young eyes. My fury was immediate and engulfing. I had my sister in my arms, one hand protectively cupping her head so swiftly that I blinked down in shock at the limbs that had reacted so protectively, so suddenly.

“Leave,” I said coldly. I never made it to practice and our friendship was never the same. Afterwards I realized I was shaking. I shuddered with racing heart and adrenalized limbs. Moonquaked. Even now I scarcely understand the ferocity of my reaction.

***

My sister has piano lessons on Monday evenings. During the summers, when home from college, I’d help her practice. One afternoon, not long ago, we were playing together. It was a little duet that she had been working on and I played the teacher’s part. The fine hairs near her temples were slick against her scalp, sweaty from playing on the swing-set in the backyard. When we finished I leaned in and kissed the top of her head. Her sweat smelled—not terrible, of course. It was not in any way comparable to the body odor produced by a pubescent boy. But neither was it the innocent, odorless sweat of a baby.

Something inside me crumbled in that moment, tiny fractures forming in my core. There were cracks in the reservoir of strength I had built that day when I had chosen not to cry. I felt this terrible shrinking feeling, though I did my best to hide it. How had this happened? When had this happened? How dare I be gone so frequently, so long? What kind of big sister is as absent as I? I knew what that smell meant, even if I didn’t want to face it at the time. She was growing, and soon she’d be a full person of her own, not that infant I had reached for in the night, but a girl who wouldn’t need me, at least not with the intense, encompassing need of a baby. I shook myself out of my reverie. After all, there was nothing I could do about it. Change is inevitable.

I poked her playfully in the side. She giggled. We went upstairs and did a little washing up before dinner. My sweaty little sister, whose hand still felt so small in mine, but whose head was cresting dangerously close to the height of my shoulder.

***

The moon’s practical role in our society today has become obsolete. It no longer provides necessary markings of the passing of time. Our culture does not depend upon it; we don’t need it anymore. But it is still wanted: its presence is still beloved. My sister no longer needs me the way she used to, and I am obsolete. But I hope that I am still wanted, still desired, still beloved. Her presence in my life changed me irrevocably… and I am without regret.

According to the Outer Space Treaty, the moon is free to all nations for exploration. Yet I am unwilling to share. The moon is ours, my sister’s and mine. And though we may not need it, as I am no longer needed, we still want it all for ourselves.