Everyone enjoys watching a sunset. To keep track of the sun's shifting position, ancient civilizations erected markers like Stonehenge. These days, our own urban grid can serve perfectly well for this purpose. Streets that are precisely aligned east-west, like those in Salt Lake City, point directly at the setting sun at every equinox (March 20 and Sept. 23).
Manhattan's streets had the setting sun sitting at their far ends like a glowing ball on May 31 and will again in two days, on Tuesday, July 12.
It's fun to witness the birth of a new Big Apple tradition, now increasingly called Manhattanhenge. Watching the orange sun dramatically set at the Hudson River end of our streets (best seen along the wider streets from 14th to 110th) is gaining annual recognition as a "thing to do." But this year, Manhattanhenge may be more than a lovely visual event. Thanks to the sun's recent strange behavior, our attention should be focused on that star for much more important reasons.
The sun grows brighter and then dimmer in a roughly 11-year cycle that was first discovered in the 18th century. The brighter the sun, the more solar storms take place, and vice versa. The sun has been cool and calm for a while. But that's over, with serious consequences for the Earth.
The most recent solar quiet period, called a "solar minimum," was stranger than any witnessed by any living astronomer. From 2006 to 2008, there was a bizarre near-total absence of sunspots, which experts believe created a slow-down in Earth's global warming and produced the frigid year of 2007.
But now solar storms are returning with a vengeance. Last month, one of the most spectacular erupted in our general direction. Fortunately, most of those 10 billion tons of material fell back onto the solar surface, and what continued outward brushed past us in a harmless glancing blow.
Researchers expect such violent activity to peak between 2012 and 2015. Here is why none of us should ignore it.
First, National Oceanic and Atmospheric Administration scientists recently concluded that carbon emissions is only one of four factors that determine global temperatures. The others are the presence of major volcanic eruptions, the Pacific El Nino pattern and, lastly, the sun's activity.
The past decade's so-called plateau in global warming was almost certainly due in part to the sun being exceptionally dim. But now that the sun is back, global temperatures have again started to rise, with last year, 2010, officially one of the three hottest ever recorded. Think about that as you stand in awe of Manhattanhenge.
There's more. The years surrounding "solar max" typically feature super-strong solar storms that throw high-speed particles in our direction. If we experience a hyper-violent storm, it could destroy satellites, kill astronauts and halt jetliner flights over the poles by creating high radiation and radio blackouts.
According to a 2008 government panel, it would disable our power grid for several years and induce trillions of dollars of damage. They concluded that such a "low frequency, high consequence event" is typically ignored - that is, until it happens.
The last such hyper-storm, in 1921, knocked out railroads and burned down houses. And that was before we had electronics, pipelines, satellites, jets flying polar routes, a manned space station or long-distance high-voltage power lines.
In the "solar max" year of 1989, a lesser solar storm plunged a quarter of Canada's population into darkness and produced extensive damage here. While new solar-monitoring satellites have greatly increased our knowledge since then, our electrical grid has grown more complex and more vulnerable.
For these reasons, this year's Manhattanhenge should remind us that the sun is not some abstract entity. Rather, our economic health and climate depend on what the sun will do during this new cycle, whose behavior is still very much unknown. Remember that as you enjoy the view.
Berman is the astronomy editor of the Old Farmers Almanac and the author of "The Sun's Heartbeat and Other Stories from the Life of the Star that Powers Our Planet," published this week.
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