At 6:29 p.m. Tuesday evening, students gathered atop the Science Center to watch an asteroid approximating the size of a city block narrowly miss a collision with planet Earth.

The passage of the asteroid some 201,700 miles from Earth marked the closest encounter since 1972.

Timothy Spahr, director of the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics, reassured students not to worry about the asteroid because the calculations predicting that the asteroid would miss Earth by a considerable distance were quite secure—a matter of “a bread and butter scientific calculation and cataloguing,” as he put it.

But because the asteroid, called “2005 YU55,” passed at such relatively proximity, students using the Loomis-Michael Observatory had an opportunity to see it up close—an occasion not predicted to occur again until 2028.

Spahr said last night’s event was of great scientific importance since asteroids have so much data to offer and are rarely seen so close to Earth. Spahr stressed that objects with the potential to strike Earth are constantly being monitored and their trajectories calculated, and that last night’s event was deemed totally “routine” as far as asteroids go.

Amanda T. Pillsbury, a student at the Graduate School of Education, described the asteroid as “a small black dot racing across the sky near the moon.” She said watching it pass by was “a very cool experience.”

Physics major Jeremy S. Cushman ’12 said that last night was “a great night for science,” but added that “if it was to hit the Earth it would be catastrophic.”

The asteroid will provide scientists with data that they have not been able to obtain before, Spahr said, thanks to technology that didn’t exist when the 1972 asteroid passed.

Spahr also said that although we are safe from this passing, there are many asteroids that scientists will be mapping in the future. It’s the “ones that are years away that we really need to worry about.”