Eclipses, Umbra and Penumbra for Dummies

Umbra vs. penumbra

Non-scientists frequently complain about "jargon" when faced with media describing scientific phenomena. Of course, non-lawyers complain about legalese, patients complain about "doctor-speak," and the list goes on. Some journalists are able to "write understandable copy" about technical topics, although that usually means defining jargon in everyday terms, thereby making the content much longer, making the "techy" stuff much shorter, or simply getting it wrong. Take, for instance, any discussion of a solar or lunar eclipse, where the words "umbra" and "penumbra" are very likely to appear. When the task of explaining "What Is The Difference Between Umbra and Penumbra?" for eHow.com (now at Sciencing.com) fell to contributor George Lawrence (aka George Lawrence JD), he showed that not everyone is qualified to translate jargon to "plain English"...
Let's see what Lawrence has to say in his introduction:

"Shadows form when light shines upon an object. While this is a simple concept, the shadow volume behind the object can reveal startling phenomena. For example, a lunar eclipse occurs only when the moon is full and when it passes through part of the earth’s shadow. Physicists describe shadow volume in terms of umbra and penumbra."

We're not sure where George came up with the idea that "Physicists describe shadow volume in terms of umbra and penumbra," since "shadow volume" seems to be graphic design jargon instead of scientific terminology, but what the hell – we'll go with it: at least he's talking about shadows instead of something totally unrelated. Lawrence takes some time to discuss the origin of the words: umbra is Latin for shadow, and the prefix pen- means... well, George says it means "hanging" but that's bull: pen- means "almost" (he must be thinking of the prefix pend-) He also blathers a bit about how the umbra is darker than the penumbra and makes another bullshit claim when he says that "The penumbra is not a true shadow. The Lighting Design and Simulation Knowledgebase describes the penumbra as a gradient..."

He meant that the darkness of the penumbra, which is not a full shadow, is variable. Duh, duh, dumbass...

Of course, if Lawrence had researched the words in the context of an eclipse instead of graphic design, he might have provided readers some useful information... but he didn't. People who actually know what an eclipse is and why there are both umbra and penumbra could have easily explained the phenomenon in terms of light, point sources, and non-point sources. George had no idea, yet held forth at length, most importantly omitting any discussion of why an eclipse has both an umbra and a penumbra. If that doesn't qualify him as Dumbass of the Day, we don't know what does...

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