Thousands of New Yorkers and tourists are expected to gather in the city's vast streets on Friday night to witness the stunning interplay of the sun and the city's itself, a phenomenon dubbed "Manhattanhenge".

Twice a year, the setting of the sun aligns perfectly with the streets that form the grid of Manhattan, creating a spectacular scene at dusk, as if the glowing sun were setting perfectly between the city's skyscrapers.

The name "Manhattanhenge" was coined by renowned astrophysicist and New Yorker Neil deGrasse Tyson, who felt the name captured the interaction between the "city and cosmos".

The phenomenon is made possible, he said in an article for the American Natural History Museum, not only by New York being a near exact grid, but also one that has a clear view of the horizon.

It occurs two times a year but does not coincide with the equinoxes, because Manhattan's grids are not aligned exactly north-south.

"Every other day, the Sun rises and sets elsewhere on the horizon. Had Manhattan's grid been perfectly aligned with the geographic north-south line, then the days of Manhattanhenge would coincide with the equinoxes," he wrote.

"But Manhattan's street grid is rotated 30 degrees east from geographic north, shifting the days of alignment elsewhere into the calendar."

The half-sun will appear on the grid at 8.12pm Friday local time (10.12am AEST Saturday), and again at 8.21pm on July 13 (10.21am AEST July 14). The full sun will appear on the following nights.

deGrasse Tyson speculated, somewhat tongue in cheek, that if future generations were to discover the ruins of Manhattan, they might guess that the phenomenon coincided with significant dates on our civilisation's calendar. Given the dates each year roughly correspond with Memorial Day and American Major League Baseball's All Star Game.

"So they would assume that America was about war and baseball," he said.