The building at 353 Prospect St. has three domes. Two of them house telescopes, but the third — and largest — houses the entire universe.

Now fully functional, Yale’s just-finished planetarium — part of the Leitner Family Observatory and Planetarium — will open its doors to the public starting Jan. 20. The completion of the $1.5 million project makes the Yale planetarium system the second of its kind anywhere in the world and marks a step forward in the center’s efforts to expand its public programs and become a central hub for astronomy outreach in New Haven.

Starting next week, the planetarium will be open every Tuesday evening for a public planetarium show, along with a special lecture presentation on the first Tuesday of each month. In the past, astronomy graduate students sponsored telescope observing nights twice a month but had to cancel them if the skies were too cloudy.

Given the weather-dependent nature of the observing nights, observatory director Michael Faison said the planetarium creates an ideal opportunity for Yale astronomy to reach out to New Haven students and families.

“Only maybe one in four Tuesdays are suitable given the weather and … we can only really handle maybe 30 people at a time out on the observing deck,” said Faison, who is also a lecturer and an associate research scientist in the Astronomy department. “But now that we have the planetarium, we’re actually going to do a lot more advertising.”

Faison plans to initiate partnerships with New Haven schools to organize field trips for local elementary and middle school students. By the end of the school year, he hopes to plan an initiative that will bring every New Haven sixth grader to the planetarium.

Tomer Tal GRD ’12, a graduate student in astronomy who volunteers regularly at the center, said astronomy depends on public involvement to be an “applicable” science.

“What we do, if it doesn’t involve and interest the public, then it kind of loses its … credentials, in a sense,” Tal said. “So, having something like this means that we can show the public what we do.”

Outreach aside, the planetarium will also be an important teaching tool, said Rachel Semple-Shuchter GRD ’13, a graduate student in astronomy, who works as teaching volunteer regularly at the center and as a teaching assistant for undergraduate astronomy courses.

The state-of-the-art system will make the teaching of hard-to-visualize concepts a breeze, she said. (All it takes is a few mouse clicks for the two high-definition projectors to illuminate a 3-D rendering of any time and place in the universe on the 30-foot diameter dome.)

Semple-Shuchter added that the public often thinks astronomy is merely about things like learning constellations, but weekly public shows will broaden individuals’ understanding of the field, both in its amateur and professional dimensions.

Given the limited staff — Faison devotes a third of his time to the observatory and planetarium, and is hoping to hire someone part-time to head-up the school-based initiatives — volunteers like Tal and Semple-Shuchter are a crucial part of the center’s success.

James Leitner ’75 agreed to fund the planetarium project in 2007 after the observatory had already been completed, and the official ribbon-cutting ceremony will take place this April along with University President Richard Levin.