WHEN: 7:30 p.m. Monday

WHERE: Steward Observatory, 933 N. Cherry Ave., Room N210

Bits of the region’s star-gazing history are the focus of Monday’s Public Evening at Steward Observatory, which will mark its 90th birthday Tuesday.

Tom Fleming, the Steward astronmer who organizes the monthly talks, will speak about Andrew Ellicott Douglass, who founded the UA Department of Astronomy and its observatory with a gift from Lavinia Steward of Oracle in 1923.

Fleming, in addition to relating the observatory’s history, will show some of Douglass’s movies, which he had transferred from 16-mm film reels to digital format.

Fleming said most of the Douglass film archive, held in the UA Library’s Special Collections, shows him at his other avocation — tree-ring studies.

Douglass invented the science of dendrochronology in an attempt to correlate climate and sunspots.

Also Monday, astronomer Laird Close will talk about telescope maker Alvan Clark, whom Fleming calls the “finest telescope maker of the 19th Century.

A 5-inch Clark refractor has been used as a finding scope for Steward’s 36-inch telescope since its inception. It has been brought down from Kitt Peak, where the original 36-inch telescope was moved, for the birthday celebration.

Weather permitting, it will be available for viewing the night sky on Monday along with the 21-inch telescope now installed in the original Steward dome.

Finally, W. John Cocke, emeritus professor of astronomy, will talk about the 1969 discovery of the optical pulsar in the center of the Crab Nebula, which brought international attention to Kitt Peak and Steward Observatory.