NEW YORK (CBSNewYork) — There is a centuries-in-the-making opportunity for people to view a “double planet.”

In Northern Virginia, Philadelphia and right here in the Greatest City on Earth, humans have their eyes and cameras are focused on something spectacular in the night sky — the Great Conjunction between Saturn and Jupiter.

“No one that’s alive today has ever seen Jupiter and Saturn this close to one another in the sky,” American Museum of Natural History astronomer Jackie Faherty told CBS2’s Vanessa Murdock.

Faherty said the Great Conjunction is a story unfolding before our very eyes. Each night, the two planets appear closer and closer.

“Just like any great story, it’s building up, and on the 21st, they’ll be at their closest point,” she said.

For optimal viewing, get a clear view of the horizon and start looking west around dusk.

“You’re not going to miss it. The thing is, Jupiter is the brightest thing in the sky,” Faherty said.

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This is the greatest of Great Conjunctions in almost 800 years.

“The closest visible one, the one that everybody around the world could easily see was in the year 1226,” said NASA astronomer Michelle Thaller.

Thaller said there was another one similarly close in 1623 – the time of Galileo – but viewing was nearly impossible.

“The problem was it was so close to the sun in the sky,” she said.

How will this Great Conjunction look to the human eye?

“Depending on exactly how good your eyesight is, they might even merge into sort of one bright object,” Thaller said.

For most, the two planets will be distinct. Still, you might hear it called the “Christmas Star,” because some wonder if the “Star of Bethlehem” that led the three wise men to Baby Jesus was actually a Great Conjunction.

There is a conjunction every 20 years, but the next one that will be this great is not until 2080.