The Astronomical Imbalance Hidden Inside Manhattanhenge

A Hidden Imbalance

Manhattanhenge is a twice-yearly phenomenon where the setting Sun aligns perfectly with Manhattan’s street grid.

Dr. Jackie Faherty, an astronomer at the American Museum of Natural History (in the Upper West Side neighborhood of Manhattan), calls it a lesson in Astronomy 101.

But not many people know there’s a bonus lesson hidden away in the details of Manhattanhenge: it’s a subtle example of an astronomical imbalance known as the equation of time.

The Roughly 7-Minute Difference

Every year, Dr. Faherty officially announces two pairs of dates for Manhattanhenge, one on each side of the June solstice.

On “Full Sun” dates, the whole of the Sun’s disk appears just above the horizon, perfectly framed by the buildings on either side of the street. On “Half Sun” dates, only the top half of the Sun is visible above the horizon.

The dates and times for 2026 are as follows.

• May 28 — 8:14 pm (Half Sun)
• May 29 — 8:13 pm (Full Sun)
• July 11 — 8:20 pm (Full Sun)
• July 12 — 8:21 pm (Half Sun)

The hidden detail is: why is there a roughly 7-minute difference between the May dates and the July dates?

It’s a subtle difference, and it’s easy to overlook its significance. “In all the years I’ve talked about Manhattanhenge, no one has asked me about the asymmetry in the timing between the May and July events,” Dr. Faherty told timeanddate.

Solar Noon

So what’s going on? Let’s begin by considering the Sun’s movement across the sky.

Every day, as seen from New York, the Sun rises somewhere in the east, reaches its highest point in the sky around noon, and sets somewhere in the west.

But there’s a bit more to it than that. To start with, the positions of sunrise and sunset change slightly from one day to the next. This is what makes Manhattanhenge such a special event: there are only a few days each year when the setting Sun aligns precisely with the grid of Manhattan.

Not only that, the time the Sun reaches its highest point in the sky changes, too. Astronomers call this solar noon: it’s when the Sun lies due south for an observer in New York.

The Sun’s movement across the sky is caused by Earth’s rotation, and our planet is an excellent timekeeper. The time it takes to complete one rotation only ever varies by a millisecond or so.

We might expect, therefore, that the time from one solar noon to the next would be exactly 24 hours—in other words, solar noon would always happen at the same time of day. However, that’s not what happens.

When Noon Shifts

Let’s look at the time of solar noon in New York on the dates of the “Full Sun” Manhattanhenge.

• May 29 — 12:53 pm
• July 11 — 1:01 pm

We can immediately see the same 7-minute or so difference in the time of solar noon. In other words, solar noons are not spaced exactly 24 hours apart, and don’t happen at the same time every day. How can we explain this?

First things first: we can also see that solar noon is happening around 1 pm rather than 12 midday. The explanation here is fairly straightforward—in March, New Yorkers put their clocks forward one hour for Daylight Saving Time.

Now for the main question. Yes, Earth’s rotational speed is extremely consistent. The catch is that Earth completes one full rotation on its axis in 23 hours, 56 minutes, and 4.1 seconds. This is the value that doesn’t change (varying by a few milliseconds over the course of a year).

The extra four minutes that give us our daylength of 24 hours come from something else. And that’s where things become a bit more complicated.

One Spin Is Not Quite Enough

Imagine it’s solar noon in New York on a Monday. As always, the Sun is moving across the sky as the Earth rotates; at the moment of solar noon, it lies exactly in the direction of south.

Now imagine the Earth makes one complete spin on its axis: this will take 23 hours, 56 minutes, and 4.1 seconds. During this time, the Sun sets on Monday evening, rises on Tuesday morning, and climbs high into the sky once again.

Crucially though, at the same time, Earth is moving around the Sun. On Tuesday, Earth is in a different place along its orbital path than it was on Monday.

As a result, even though the Earth has completed one full rotation, the Sun doesn’t lie in exactly the same direction as the day before. The Earth needs to rotate a tiny bit more for the Sun to be exactly due south once again.

This is where those extra four minutes that give us our 24-hour day come from: it’s the additional time needed for Earth to complete one spin with respect to the Sun. In this example, it’s taken us from solar noon on a Monday to solar noon on a Tuesday.

The complication is that the amount of additional time required changes throughout the year.

Two Complications

There are two reasons why a day according to the Sun is almost never exactly 24 hours long.

First, the Earth-Sun distance is constantly changing. A consequence of this is that Earth’s orbital speed is constantly changing, too. At its fastest, Earth travels along its orbit at 30.3 kilometers per second (18.8 miles per second); at its slowest, it travels at 29.3 kilometers per second (18.2 miles per second).

Second, Earth’s rotational axis is tilted by 23.4°. At the solstices, one of the hemispheres is tilted toward the Sun; at the equinoxes, neither hemisphere is tilted toward the Sun. This is what gives us our seasons and seasonal phenomena such as Manhattanhenge. What it also means is that the angle of the Sun’s path across the sky varies over the course of the year.

Both these factors affect how long it takes the Sun to travel from one solar noon to the next—from around 30 seconds more than 24 hours, to around 21 seconds less than 24 hours.

The Equation of Time

Over the weeks, these day-to-day changes can add up to many minutes. It all means that during some parts of the year, the Sun gets ahead of our clocks and watches, and solar noon happens earlier than we might expect. During other parts of the year, the Sun falls behind our clocks, and solar noon occurs a bit later in the day.

The exact number of minutes the Sun is either ahead or behind is given by a chart that astronomers refer to as the equation of time.

Back to Manhattanhenge

Just as the times of solar noon shift forward and backward over the year, so too do the times of sunrise and sunset. And this gives us the explanation for why Manhattanhenge happens around 7 minutes later in July than it does in May.

If we look at the chart above, we can see that around May 29, the pink line is in the top half of the chart: the Sun is running a couple of minutes “fast” compared to our clocks and watches. Around July 11, the pink line is in the bottom half: the Sun is five or so minutes “slow.”

Overall, the Sun follows the same path across the sky on both dates. But on July 11, it arrives at the sweet spot—aligned with Manhattan’s street grid, just above the horizon—a handful of minutes later.

“Astronomy In Your Face”

The equation of time is a subtle and generally overlooked concept. But the fact that the Sun gets out of step with our clocks and watches has real-world consequences. For instance, it means that our earliest sunrise and latest sunset don’t coincide with the longest day of the year.

Still, these details are easy to miss. One of the illuminating things about Manhattanhenge is how it reveals the imbalance on a city-wide scale.

As Dr. Faherty says: “Manhattanhenge is really astronomy in your face.”

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