"It's supposed to be spring," one small, cold boy complained to his friend. Many of the smaller children, not yet bar mitvahed, wore T-shirts bearing an image of the sun and hats that read "The Moment."
According to Jewish tradition, the sun returns every 28 years to its original place in the divine creation of the heavens.
Official sunrise for the eastern United States was 6:34 a.m., and layers of pale pink appeared on the gray horizon starting around 6:15. But broken clouds and the urban skyline delayed the Philadelphia moment to 6:49 a.m., when rays of the sun broke through a seam in the clouds.
At that, Rabbi Yehudi Shemtov led the crowd in a Hebrew prayer known as the "Blessing of the Sun."
"Praise the Lord from the heavens; praise Him in the celestial heights," it began. "Praise Him all His angels; praise Him, all his Hosts...praise Him, all the shining star...Let them praise the Name of the Lord, for He commanded and they were created."
Minutes earlier Rabbi Shemtov, head of Chabad of Bucks County, reminded the crowd that though they face the sun and bless it, the prayers are directed to God.
After the blessing his father, Rabbi Abraham Shemtov, called the moment a "time to be inspired."
The senior Shemtov, head of the Philadelphia area Chabad and a leader of the international hasidic Lubavitcher movement, also called on the gathering carry the morning celebration to into tonight's seder, the annual Passover dinner that marks the Jews' flight from Egypt.
Charles Schnur, 30, said he came to the rooftop to partake in the blessing "because it's once every 28 years. I just like this."
"It was a once in a lifetime moment," exclaimed one young man riding down in the elevator afterwards.
"It better not be," said his friend. "I'm hoping to be around for the next one."
Contact staff writer David O'Reilly at 215-854-5723 or email@example.com.