All my life, I have taken comfort in the constancy of the skies. Even as the Sun, Moon, and planets continuously cross the sky, their movements are completely predictable and dependable. Last summer, for instance, tens of millions of Americans planned their travels and parties for the few hours of “The Great American Eclipse.” This July, Mars will dominate as the fourth brightest object in the sky (after the Sun, Moon, and Venus) when it passes within 36 million miles of Earth—the second closest pass in 60 thousand years! Because of the constancy of the skies, we can calculate, predict, and enjoy with certainty.

The American poet, Robert Frost, writes, “You'll wait a long, long time for anything much / To happen in heaven beyond the floats of cloud,” lines that suggest to me a kind of disappointment. He goes on to write, “We may as well go patiently on with our life, / And look elsewhere than to stars and moon and sun / For the shocks and changes we need to keep us sane.” I vehemently disagree…I don’t need “shocks and changes” to keep me sane; I feel an unreasonable comfort knowing where and when the Sun and Moon will rise and set…their predictability gives me sanity, security. The sky does not disappoint.

Of course, the skies offer a constancy of beauty as well: the brilliant winter constellations, Orion and Canis Major with our brightest star, Sirius; summer’s predictable but surprising Perseid meteor shower; solar and lunar eclipses; the elaborate, colorful images of planets, especially as the images get bigger and better—Jupiter’s storms, Saturn’s rings, the blue-green of Uranus, the deep blue of Neptune, the red of Mars; and Pythagoras’s “Music of the Spheres,” the slow interlaced orchestration of barely perceivable movement every night.

The moon, in particular, moves noticeably and predictably every night, a confirmation that days go on, the world goes on, the universe goes on. With neither weather nor atmosphere, the surface of the Moon is nearly unchanged since I first started watching it decades ago, nearly unchanged since Ptolemy watched it in the Second Century or Columbus watched it when he sailed the Atlantic in 1492! Tonight, April 15, 2018, the Moon will be New—invisible in the glare of the Sun. Then, each evening, it will appear as a slightly larger sliver than the evening before, a little higher in the sky. When so much else around us seems shocking and changing, I welcome the constancy of the skies.

A few years ago on a sunset cruise in Florida, the first mate on board—who served as “tour guide” for the sunset—had no idea about the skies, even though he sailed every evening at sunset. Sailing on the day after the New Moon, I told him to expect to see a thin crescent of Moon just above the horizon after the Sun had set. I was shocked when he pointed to the east and said, “No, the Moon comes up over there.” I explained that it crosses the sky every month (the word “month” comes from the word “Moon”): from newly waxing crescent in the west just after sunset, to Full Moon rising in the east opposite the sunset, to waning crescent just ahead of sunrise. He thought I was crazy until a few minutes after sunset, the skies darkened to show a slip of crescent Moon above the western horizon. Soon, Venus was visible, then later Mars, then Jupiter. I knew they’d be there…the sky does not disappoint.