Half and Full (photos via mrgeneko's flickr and michaelnyc's flickr)

Manhattanhenge is making its 2015 debut this weekend, and for those who don't know about the Event—which was first named and noticed by Neil deGrasse Tyson—here's a little primer.

In short, Manhattanhenge is when the sunset aligns perfectly with the city's grid. This happens twice a year with a full sun, and twice a year with a half sun—all four times the sun illuminates both the north and south sides of every cross street of the borough's grid. It is our Stonehenge, and deGrasse Tyson has declared it to be "a unique urban phenomenon in the world, if not the universe."

What it really means though, is that there will be groups of people standing in the middle of the street this evening trying to capture the perfect shot to Instagram (#nofilter).

#Manhattanhenge #paparazzi #mobscene #unionsquarenyc #sceneinnyc

A photo posted by Scene In NYC (@scene_in_nyc) on

Tips from NdT: "Position yourself as far east in Manhattan as possible. But ensure that when you look west across the avenues you can still see New Jersey. Clear cross streets include 14th, 23rd, 34th. 42nd, 57th, and several streets adjacent to them. The Empire State building and the Chrysler building render 34th street and 42nd streets especially striking vistas."

Half Sun on the Grid

Friday, May 29 8:12 P.M. EDT
Monday, July 13 8:21 P.M. EDT

Full Sun on the Grid

Saturday, May 30 8:12 P.M. EDT
Sunday, July 12 8:20 P.M. EDT

It's recommended you get there 30 minutes early... and as we learned from Sarah Jessica Parker, don't even bother if it's cloudy.