To teach their children about the earth, the Navajo people told a story about the stars.

One morning, as the story went, seven boys went out to hunt, armed with bows and arrows. They walked a great distance, finally disappearing behind a mountain. Desperate to get their crops in the ground before it became too late, their families began planting, reasoning they could look for the boys when the sowing was done. But by the time they looked up from their labors, the boys had returned.

For the Navajo, says UVA associate astronomy professor Ed Murphy, these so-called Hard Flint Boys were represented by the Pleiades, which pass behind the sun annually at the Spring Equinox. Their disappearance meant it was time to begin planting.

Cultures from the Mayans to the Australian aborigines to the Aztec have legends about the stars that correspond to agricultural timetables, Murphy says. Stars not only represented glittering mythological stories, they also signaled the appropriate time to sow and to harvest, to celebrate or hunt.

“What’s amazing about it is that every culture did this,” says Murphy. “They all invented stories about the sky to teach their children. That was important to their survival because if you are a family and feed your family by corn you need to know when to plant the corn and then harvest your corn.”

Since the beginning of recorded time, stars have been used to program humanity’s days. Calendars were unreliable and not always available, but the stars were signposts of the earth’s rhythms.

“The sky was humanity’s first calendar,” says Murphy. “The sky was something that was constant from year to year. If a certain type of sighting happened at one time of the year it happened every time.”

The giant yellow star in the constellation Virgo, for instance, called Vindemiatrix, signaled to vintners when it was time to plant grapes and when to harvest them. The Ancient Egyptians, Sumerians, Greeks and others used the day a star first reappears in the morning sky after a period of absence—called its heliacal rising—to time agricultural routines or schedule cultural celebrations, like the beginning of the New Year or the commemoration of the dead.

In ancient Egypt, the heliacal rising of Sirius, the brightest star in the sky, was used to determine the time of the Nile’s flooding. That crucial event left behind a deposit of rich, black silt that helped determine the region’s agrarian health.

While spring may not be the best time to view stars—the bright winter constellations are rapidly disappearing and the Milky Way is not yet visible—it held important meaning for ancient cultures.

“It is filled with constellations whose stories are about time, renewal and planting crops,” Murphy says.

Those constellations can be harder to see in modern times. Light pollution—the illumination of the sky by electric lights—obscures many of them. The National Park Service estimates that two-thirds of Americans cannot see the Milky Way from their backyards and nearly all live in places with measurable light pollution.

“Even in Charlottesville, you no longer get to see the Milky Way,” laments Murphy. “When you’re standing on top of Observatory Hill, you can see all the lights of Charlottesville and people say it’s beautiful. But I like to point out how every light you can see is ruining the night sky.”