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September 25, 2008

How dark is your sky?

I received an email message the other day from Mike Shriver, in Linthicum. He was outside stargazing one morning recently. The sun was not up yet, and Mike spied Orion, The Hunter, rising in the east.

Orion is usually thought of as a winter constellation. Its bright trio of stars at The Hunter's belt is easy to spot, and it's surrounded by other bright stars - Betelgeuse, Rigel and Bellatrix are the best-known. The belt includes Mintaka, Alnilam and Alnitak. Great names, all.

Sailors, I've heard, hated to see Orion reappear each autumn, because they knew it's return meant the advent of violent winter storms. Or was it Capella?

But for backyard stargazers, Orion is an old friend, easy to find, and a kind of pointer for other treasures of the winter sky. Off to the east is Sirius, the brightest true star in the sky. To the west lie the Pleiades, or Seven Sisters, a jewel-box of a star cluster, especially in binoculars. And just below Orion's Belt lies the Orion Nebula, a cloud of glowing gas and young stars just visible to the naked eye, and a complex wonder through even a small backyard telescope.

Anyway, the sight of Orion sparked a memory in Mike's head.

"It made me think of an article I saw in the Sunpaper maybe two or three years ago. Maybe you had something to do with it. Maybe not. Anyway, if I recall correctly some organization was doing a study on air and light pollution. As part of the article, there was a diagram of the stars in Orion and they were asking readers to cut out the diagram. Then they were to go outside on a clear night and circle the stars on the diagram that they could actually see, and then mail it in. Apparently (once again, if I recall correctly) the results were going to be tabulated in some fashion and then published. I was wondering if this rings a bell with you. I would have been curious to see the results."

Good memory. It was the Enlighten Maryland project. We ran a story in The Sun in February 2002, along with a star chart of the constellation Orion. Readers were asked to go outside and find Orion, then circle only the stars on the chart that they could see with the naked eye. The thought was that, where light pollution was the worst, fewer of the stars would be seen. By piecing all the returns together, the project could construct a map of light pollution in Maryland.

I never heard anything about the results, either, at the time. I called Max Mutchler, at the Space Telescope Science Institute on Thursday and asked him about it.

Enlighten MarylandHe said the project received 1,130 returns (some of them at left), and ernest efforts were made to convert the data into a contour map of the light pollution in Maryland. But the reporting turned out to be inconsistent, perhaps because such a broad range of observers participated -  from school kids to amateur astronomers. Anyway, he was never able to put together a map that looked right to him.

"It was fun to try to refine the data and see if the results made any sense, but I wouldn't want people to read too much into it," he said. So, for whatever it's worth, here's what they came up with. Credit goes to Max Mutchler, Brian Eney and Melissa Jan, of Enlighten Maryland. The lighter colors represent the brighter skies and higher light pollution levels. The darker colors represent darker skies and better stargazing.

Enlighten Maryland

Like I said, it's a little rough. Here's a map of the locations across Central Maryland where the reports came from.

Enlighten Maryland 

If you want to see another light pollution map that covers the whole globe, I'll give you a link here.  Just click on the map for North America, and click to open the high resolution TIFF image. Then click on the little magnifying glass, and then on Maryland to zoom in to a scale that's useful. You can see the dark region in north central Pennsylvania, where you'll find dark skies preserved at Cherry Springs State Park. Out in West Virginia there are also some fine, dark skies.

You can also go to for leads to the best nighttime skies in the nation.


Posted by Frank Roylance at 3:40 PM | | Comments (1)
Categories: Sky Watching


In October you can participate in the Great World Wide star count.
In March there is Globe at Night .Visit for light pollution info.

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About Frank Roylance
This site is the Maryland Weather archive. The current Maryland Weather blog can be found here.
Frank Roylance is a reporter for The Baltimore Sun. He came to Baltimore from New Bedford, Mass. in 1980 to join the old Evening Sun. He moved to the morning Sun when the papers merged in 1992, and has spent most of his time since covering science, including astronomy and the weather. One of The Baltimore Sun's first online Web logs, the Weather Blog debuted in October 2004. In June 2006 Frank also began writing comments on local weather and stargazing for The Baltimore Sun's print Weather Page. Frank also answers readers’ weather queries for the newspaper and the blog. Frank Roylance retired in October 2011. Maryland Weather is now being updated by members of The Baltimore Sun staff

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