Exploring the science of the winter solstice

Science Center celebrates moment days start to grow

December 22, 2008|By Frank D. Roylance | Frank D. Roylance,frank.roylance@baltsun.com

Our ancestors banged on drums and lit bonfires to chase away the evils and deprivation of winter, push back the dark boundaries of the year's shortest day and revive a dimming sun.

Yesterday, the first day of the northern winter, when the sun reached its lowest angle in the midday sky, it was an excuse to give the kids a peek through an antique telescope at the Maryland Science Center.

That seemed cool enough to Marian Comi-Morog, 10, a Cathedral School student from Baltimore. She clambered up an aluminum stepladder for her first-ever direct look at the sun, through the Crosby Ramsey Memorial Observatory's 1927 Alvan Clark & Sons telescope.

"I was surprised you could actually see the sun," she reported. "It was really very big and red. And it had some orange, and it had, like, little things going all around it."

The "little things" were probably the shimmer at the edge of the sun's disk, caused by turbulence in the Earth's atmosphere.

But visitors to the observatory also caught a glimpse of a solar prominence - a geyser of hot, glowing gas, four or five times the diameter of the Earth - launched from the sun's surface by magnetic energy.

Through the 8-inch refractor telescope, this colossal eruption was a thread-like arc of pink light, barely visible, hanging from the sun's rim.

The winter solstice occurred at 7:03 a.m. yesterday, 19 minutes before sunrise. Sunset came a scant 9 hours and 24 minutes later. Change will be undetectable for a while, but from that moment on, the hours of sunshine in the northern hemisphere began to grow longer, an expansion that will continue until the summer solstice arrives June 21.

On that day, Baltimore will see sunshine for 14 hours and 36 minutes.

The Science Center's observatory is open for solar observations every Saturday and Sunday, weather permitting. Most of yesterday's morning clouds blew off just in time for observatory manager Rich Stein to offer visitors a solstice-day look at the Earth's nearest star.

For Marian's little brother, Nathaniel, 7, the thin clouds still skidding across the sun's otherwise blank disk seemed to put it in motion. "It was spinning," he said.

It also appeared blood-red, thanks to the hydrogen-alpha filter Stein attached to the telescope, both to protect visitors' eyes and to reveal the solar eruptions, which are otherwise invisible to the human eye.

There were no visible sunspots. The sun is just past "solar minimum," the point in its 11-year cycle when it is least active, and shows the fewest dark sunspots, Stein explained.

On good days, 100 or more weekend visitors might show up for a safe glimpse of the sun, part-time observatory staffer Joe Miko said. Their most frequent reaction? "It's, 'Wow!' " he said.

As the sun hung low in the south, over the rooftops of Federal Hill, Stein and Miko handed out sun viewers fitted with eye-safe No. 14 welders' glass. Nathaniel and Marian grabbed theirs and got an altogether different look at the sun.

"It looked green," Marian said. "It was very strange for me 'cause I've never seen it like that before."

Neither had her parents, Anne Comi and Nick Morog, both new members of the Science Center. "I didn't really know what to expect, but I wasn't disappointed at all," Comi said. "And the kids enjoy this sort of thing. Marian is really into science."

Cliff Jones was the guide on the Davis Planetarium's afternoon tour of the night sky, which included an explanation of the solstice.

The days grow short and the nights grow long at this time of year because the Earth's spin axis is tilted about 23.5 degrees. That tips the North Pole away from the sun in winter, he told the 20-or-so people in the theater.

With a chain of "suns" projected across the planetarium's dome, he demonstrated how the sun's track across the sky appears to slip southward in the fall, growing shorter each day as the winter solstice nears.

As the northern summer approaches, the Northern Hemisphere tilts toward the sun again; the sun's path across the sky climbs higher, and there are more hours from sunrise to sunset.

The winter solstice might not get much attention from the public anymore. But the natural world continues to respond to the changing length of the day and night.

As museum visitors looked through the rooftop telescope yesterday afternoon, a flight of honking geese flew high over the observatory dome, their ragged V formations pointed south.

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