The first Thanksgiving night sky: What did the Pilgrims see when they looked up?

What did the starry sky look like on the occasion of the very first Thanksgiving? And what was the state of astronomy back then? It may come as a surprise to many of you that almost everything we know about the first Thanksgiving comes from a single eyewitness report. 

In September 1620, when the Mayflower finally set sail after three abortive attempts from England, there were 102 passengers and a crew of about 30 on board. When they made landfall on Cape Cod in early November, these pilgrims continued their journey to what ultimately would become Plymouth by late December, eventually forming the first permanent settlement of Europeans in New England. Sadly, about half of those passengers who made that perilous trip on the Mayflower died during the harsh winter of 1621. But those that survived were able to secure peace treaties with neighboring Native American tribes and built a largely self-sufficient economy within five years. 

It was a man by the name of Edward Winslow, one of those on board the Mayflower and who survived that first frigid winter, who wrote about the first Thanksgiving. Today, in the United States, we celebrate Thanksgiving on the fourth Thursday in November. But 400 years ago, the pilgrim's first Thanksgiving took place over a three-day interval. It was a veritable feast that was considered a celebration of the harvest. 

Related: A brief history of Thanksgiving turkey in space 

Unfortunately, there is uncertainty as to exactly when this celebration took place. Ironically, for an event that is revered among the annual holidays today, Winslow's account — written in the form of a letter — did not provide a specific date and his description was relatively brief, but most reference sources today indicate that it presumably occurred sometime between late-September and mid-November. 

William Bradford, Plymouth's governor in 1621, also wrote of the event in "Of Plymouth Plantation," his chronicle of the colony, but he too gave it relatively short shrift and did not write about his recollections until more than two decades after the feast itself. 

Calendrical confusion

Adding to the confusion, the dates referred to by Bradford, were made using the old Julian Calendar. In 1582, Pope Gregory XIII refined the Julian Calendar mathematically, because the Julian calendar system had not perfectly calculated leap years and had caused the calendar dates to become out of sync with celestial and religious events. 

The difference between the Julian and Gregorian calendars amounted to 10 days. Most of the civilized world was using the Gregorian Calendar, but England, unhappy with the Church of Rome, refused to go along with the new calendar. That is why the date when the Mayflower finally began its journey across the Atlantic was listed as Sept. 6 "Old Style," whereas in the Gregorian Calendar that date is recognized as Sept. 16. They made landfall on Nov. 9 (Old Style). Not until more than a century later — in 1752 — would England (and its American colonies) convert to the Gregorian Calendar. 

Rudimentary exploration

So far as the pilgrim's knowledge of astronomy was concerned, celestial navigation took the form of measuring the altitude of the North Star, Polaris at night and the sun at noon. Incidentally, Polaris wasn't as good a pole star as it is today, being 2.8 degrees from the celestial pole due to the wobbling of Earth's axis known as precession (in our time, Polaris is only two-thirds of a degree away from the celestial pole). 

Navigation in those days was imprecise to say the least. While latitude was easy enough to determine on a clear night or sunny day, determining longitude was at best, an educated guess. Stormy weather encountered during the second half of their 66-day voyage pushed the Mayflower off course; their intended destination was the mouth of the Hudson River, which was considered to be North Virginia back then. But as we all know now, they actually ended up near Cape Cod, roughly several hundred miles to the northeast. 

We don't know if anyone brought along a telescope — a relatively new invention developed by a Dutch spectacle maker just a decade before. 

The night skies of November 1621

Since the harvest feast might have occurred as late as mid-November, and since our own Thanksgiving celebrations also occur that month, let's turn our minds backward to Nov. 5, 1621 (Old Style), which corresponds to Nov. 15, 1621 on our current Gregorian Calendar. What would the night sky have looked like?

They were, in many respects, familiar skies. The constellations — the patterns that the stars form in the heavens — were the same then as now. Those stars are so distant that, although they move through space at speeds measured in miles per second and though most are traveling helter-skelter in different directions, their movements are not apparent to the human eye, even over a span of 400 years. 

But there were also wanderers in the sky: the moon and the planets. On this selected night, as soon as darkness fell, a lovely sight awaited those looking low toward the southwest. There we would have seen a slender sliver of a crescent moon and hovering a few degrees to its lower left would be the dazzling "evening star," the planet Venus. Both would have been in view for a couple hours after sunset. 

After they left the sky, we could look for Mars, shining brightly with a yellow-orange tinge against the dim stars of the constellation Capricornus, the sea goat. Mars set in the southwest at mid-evening, around 9 p.m. local time. Meanwhile, two more planets were ascending the east-northeast sky to take its place. Both are in the constellation of Gemini, the twins. First comes Jupiter, followed by Saturn; reminiscent of what is playing out in our current evening sky of 2020 with both planets evident after sundown in our southwest sky. 

Back in 1621, these two bright luminaries mixed in with the brilliant stars of the impending winter season, led by Orion, the hunter. In all, it would have been a glorious celestial scene for any of the pilgrims who gazed skyward during that first Thanksgiving.

Related: Get ready for the 'Great Conjunction' of Jupiter and Saturn

Looking back in time

We see many stars by light that started its immense journey before our country was born. Are there any stars that are just 400 light-years away? Because of the difficulty in measuring parallaxes (distant objects' changing positions when viewed from Earth), astronomers cannot determine such distances with an accuracy of one light-year. However, the 2020 "Observer's Handbook" of the Royal Astronomical Society of Canada, in its table of 288 brightest stars, lists two that are above the horizon on November evenings that are 400 light-years away: Third-magnitude Algenib, the star in the lower left corner of the Great Square of Pegasus, and second-magnitude Almach, at the end of the chain of stars marking the constellation of Andromeda, the princess. If you see either of these stars on your next clear night, keep in mind that you are looking at light that started on its journey to Earth about the same time that the first pilgrims were arriving in what we now call the state of Massachusetts. 

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications. Follow us on Twitter @Spacedotcom and on Facebook.