Grand CentralTerminal celebrated its 100th birthday this week, after opening precisely at midnight on Feb. 2, 1913.
Approximately 700,000 people pass through Grand Central Terminal each day, making it America’s busiest train station. But even with that amount of traffic, travelers might miss some small details about Grand Central. Here are five secrets the station holds that are hidden from the eyes of everyday passersby.

The Whispering Arches — Dubbed the “whispering gallery,” this set of low arches is located in front of the famous Oyster Bar. When two people stand in opposite corners of the arched entryway and whisper into the wall, they can hear the other person as if they were standing right next to each other. The arches allow a person’s voice to carry across the curved, domed ceiling to the other side of the terminal.

The Mirror Zodiac — The main concourse’s ceiling is a mural featuring 2,500 stars and depicting the Mediterranean sky as it appears in October. It is believed that Paul Helleu, the artist, painted the zodiac backwards to show how it would look from the perspective of the gods.

Sky’s the Limit — Look carefully above the zodiac’s fish constellation, and you can spot a small hole, which was made to accommodate a rocket that NASA displayed in the terminal in the 1950s. Due to a measuring mistake, the rocket turned out to be six inches too tall for the concourse, and the hole was made to help it fit. Next to the constellation Cancer, a small, black rectangle remains from the days prior to renovation to show visitors how dirty the ceiling once was. In fact, when the black rectangle was analyzed, scientists found that it was mostly tar from cigarette smoke.

Departure Times — Running late to catch your train? You may have a few more minutes than you think. Every time displayed on the departure boards is ahead by exactly one minute. According to Yahoo News, the reason behind this inaccuracy is to keep people from rushing to meet their train and consequently falling and injuring themselves.

The West Staircase — The main concourse at Grand Central has two identical staircases, which share the same design, masonry and marble, directly across the room from each other. However, to be able to differentiate the original staircase from the one was built during renovations, architects designed the west staircase to be exactly one inch shorter than its eastern counterpart.

Bryna Shuman is a staff writer. Email her at [email protected].