At age 85, Greenstein returned to Caltech's Palomar Observatory north of San Diego for one last night of observing. He gamely climbed into the small observing cage suspended above the Hale telescope's 200-inch primary mirror.

Greenstein came to Caltech in 1948, just as the university was finishing construction of the Hale telescope, the largest of its kind for more than 40 years. As the founding member of the Caltech astronomy department, he taught all of its courses during his first year and oversaw the growth of the department into one of the most prestigious in the world.

Greenstein's wife of 68 years, Naomi Kitay Greenstein, died earlier this year. They met when Greenstein was a 16-year-old undergraduate at Harvard. Her renowned hospitality and party-giving were long considered a major part of the Caltech astronomy department's appeal.