Lunar cycle creates noon moon

As with the summer sun, moon hasn't been setting above Anchorage

Posted: Monday, September 18, 2006

ANCHORAGE - Something lunar is happening, although with all these clouds looming about, who would know it.

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From the Anchorage vantage point, the moon isn't quite setting. Instead, it's just skimming the northern horizon before heading back up into the sky. Think of sundown at summer solstice at the Arctic Circle, only substitute the moon.

Then, 12 hours later, the moon is exceptionally high in the sky, higher on average than it's been in the past 70 years.

Why 70? That's just how the moon is. Its cycles are nuts.

The chance to see this midnight-sunlike moonset doesn't come very often, only for several monthly cycles every couple of decades.

Ralph Hulbert, a consulting engineer from Palmer, has been waiting a long time for this.

In Anchorage, Wednesday offered the first chance this month to see the moon slide down the east ridge line of Denali, not quite set behind the mountains, then rise up into the sky. Although skies were clear Wednesday and the night looked promising, haze in the distance got in the way of seeing the moon at due north, the point at which Hulbert would have heard the cosmic crashing of inner cymbals.

But no.

In the late 1980s, his curiosity got tweaked while he was driving the Glenn Highway to Palmer one clear winter afternoon. The moonset wasn't exactly at due north, but it was darn close. That's odd, he thought.

Intrigued, Hulbert launched into a self-assigned research project and learned the phenomenon would not happen again for nearly 20 years. As the next cycle - 2006 - approached, he produced a mind-numbing 10-page document called "Where is the Lunar Arctic Circle?" - the local point at which the moon won't set - and gave it to his kids at Christmas as stocking stuffers.

"Uhh, thanks, dad."

There's no official term for this lunar event, which occurs, specifically at this latitude, every 18.6 years. The Geophysical Institute at the University of Alaska Fairbanks confirmed that last November when those living north of Delta Junction got their best shot at seeing this thing.

The long explanation is excruciatingly long.

"The moon's position is not a simple astronomical calculation," Hulbert said. "It's one of the most complicated out there. That's where we get lunacy."

The short explanation is very short:

"It's a chance to see the moon where it's not been seen before."

The complexity of the moon's orbit is responsible for this lunar event.

The moon rises and falls rhythmically in the sky as it does elliptical laps around Earth. It moves at an average speed of 2,287 mph, three times that of a .22-caliber bullet. The result is a wobbly orbit that arrives at its highest position only every 18.6 years.

This rare moon-gazing opportunity continues over the next couple of nights. If weather cooperates, and forecasts are saying it has no intention of doing so, the best times for viewing will be today at 9:20 p.m. and Saturday at 10:20 p.m.

There will be chances to catch the tail end of the cycle over the next few months.

"We've basically got the next three or four months and that's it," he said.

Hulbert has compiled NASA and Navy predictions for those dates and times. To see them, go to http://www.AlaskChem.com, and click on "moon." You'll also find a detailed explanation of the lunar Arctic Circle document he put together.

In Anchorage, the best viewing spots include the Glen Alps, a tall building downtown or any place up high with an unobstructed view to the north.



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