A clock tower that runs counterclockwise every afternoon

Quick explanation

Seeing a tower clock reverse in daylight

If you stand in Old Town Square in Prague and look up at the Astronomical Clock, you’ll notice something people often don’t think to check: which way the hands actually move. A few tower clocks around the world are set up so the hands travel the “wrong” way, and some are even configured to change behavior at certain times. When people describe one that runs counterclockwise every afternoon, it’s usually not magic or a glitch. It’s a deliberate mechanism that switches which drive train is engaged, so the hands are being pushed from the opposite side for part of the day. The exact schedule varies and isn’t always publicly documented.

Counterclockwise isn’t as rare as it sounds

A clock tower that runs counterclockwise every afternoon

Common misunderstanding

There isn’t one single famous “afternoon-reversing” clock tower that everyone agrees on. Instead, there are scattered examples of tower clocks that run counterclockwise all the time, plus a smaller number with special behaviors tied to demonstrations, festivals, or local tradition. Prague’s Astronomical Clock is often mentioned in this broader category because its display can be read in ways that confuse the usual “clockwise” expectation, even though it’s more complex than a simple three-hand dial. Another well-known example is the backwards-running clock at the Jewish Town Hall in Prague (with Hebrew numerals), which is explicitly designed to run counterclockwise. These cases make the basic idea familiar: a public clock can be intentionally “wrong” and still be perfectly accurate within its own rules.

What has to change mechanically for a hand to run backward

A traditional tower clock is a stack of gears driven by a weight or a motor. The hands are attached to an arbor that turns at a fixed rate. To make the hands go counterclockwise, you don’t reverse timekeeping itself. You reverse the direction of rotation at the point that drives the hands. That can be done with an extra idler gear (which flips direction), a differential-like gear arrangement, or a second drive path that engages a different gear train.

If the clock reverses only in the afternoon, there also has to be a switching method. Older installations might use a cam and lever that physically shifts a clutch at a set hour. Newer systems can do it with a programmed motor drive. One overlooked detail is backlash. When gears change direction, the tiny amount of play between teeth shows up as a visible hesitation, or a hand that “jumps” a fraction before settling into steady motion.

How an “afternoon reversal” could be timed without breaking accuracy

Real-world example

The hard part isn’t making something turn backward. It’s keeping the displayed time consistent with a known reference. A tower clock that reverses for a few hours can stay “right” in two broad ways. One is that the dial itself is designed for reverse reading, so counterclockwise motion still maps cleanly onto a normal 12-hour cycle. That’s how permanently backward clocks usually work: the numbers are arranged so the system is internally consistent.

The other approach is more theatrical: the clock may intentionally show an offset or a mirrored “show mode” in the afternoon, then switch back later. In that case it’s not trying to be a reliable time source during the reversed period. Some installations solve this by separating timekeeping from display. A hidden master clock keeps correct time while the public hands are driven as a controllable output. When the display returns to normal mode, it can be walked forward quickly, or repositioned, to match the master again.

Why anyone would build it that way

Sometimes it’s a local identity marker. A backwards dial is instantly memorable, and it’s a small, harmless way for a building to have a “thing.” In places with historic clocks, it can also be a deliberate nod to older reading conventions, religious symbolism, or a specific community tradition. In Prague’s Jewish Town Hall, the counterclockwise motion and Hebrew numerals are part of the point, not a prank.

Other times it’s about controlling attention. A clock that changes behavior at a predictable time creates a daily moment when people look up together. The overlooked practical constraint here is the bell and strike system. If the tower also chimes, it may be driven by the same timing source as the hands. Reversing only the hands while keeping the strike schedule normal requires decoupling those systems, which adds cost and complexity and is one reason “afternoon-only” reversals are less common than fully backward clocks.

What an observer can actually notice from the street

From ground level, the easiest tell is the minute hand. On a large dial it moves slowly, but you can spot direction if you pick a reference mark and wait. The second hand, if the tower even has one, is often missing because it’s hard to see and adds wear. So people rely on the long hand and their own expectation, which is why a reversed clock can go unnoticed until someone points it out.

If the clock switches direction at a set time, the transition itself can be visible. There may be a brief pause, a tiny recoil, or a slightly uneven first minute as the mechanism takes up slack. On some towers, you can hear it too: a muted clunk from a clutch engaging, followed by a different motor pitch. It’s the kind of detail that only shows up when you happen to be there at the right moment, standing still long enough to watch a public object behave like a machine.