THE SOUTHWORTH PLANETARIUM 207-780-4249 www.usm.maine.edu/planet 70 Falmouth Street Portland, Maine 04103 43.6667° N, 70.2667° W Founded January 1970 "Snow? At this time of year?!" THE DAILY ASTRONOMER Wednesday, February 24, 2016 Magnetic Fields and Medusa Time now to visit Pandora's Vessel. For those who've just joined, this vessel contains oodles of parchment paper on which subscriber questions have been inscribed. During our absence, we received a few inquiries that we have now stored in the vessel. We promise to attend to them as soon as we can. And, please continue to send your questions to [log in to unmask] Today, we'll split our time between science and mythology. Yes, you are certainly able to send us your mythology questions as well as queries pertaining to science. The advantage of mythology questions over science questions is at least with the former we won't be out of our depth (as much) and, if knowledge proves insufficient, we can just make up an answer. Something that we would, of course, never do with an astronomy question! Also, the subscribers who submitted today's questions both requested to remain anonymous, so I amused myself with the pseudonyms. "I heard that we are here breathing all this oxygen because our planet has a powerful magnetic field to keep the atmosphere in place. I thought the magnetic field was high above the atmosphere, so how can it affect it at all?" -D. Trump Earth is enveloped in a magnetosphere: a magnetic field generated by the planet's highly metallic interior. Earth's core behaves like a geodynamo that sustains this magnetic shielding. This magnetic field protects Earth from the constant onslaught of solar winds: a stream of charged particles the Sun emits through space. Were Earth unprotected, these charged particles would literally "wick away" the atmospheric gases. Some researchers believe that this solar wind erosion mechanism has stripped away much of the Martian atmosphere which was once thicker than Earth's. So, although Earth's magnetosphere extends high above Earth, it helps the planet retain the rich oxygen stores found near the surface. "I read something about the mythology of Medusa. It is said that Medusa and the other two gorgon sisters lived at the farthest edges of the world where neither the Sun nor the moon ever shone. If that is the case, how did Perseus see Medusa's reflection in his shield when he cut off her head? Also, if they had torches or some other light source, then why didn't the sisters' petrify each other when they exchanged glances? This is actually irking me, so whatever answer you can provide would be a great help." B. Sanders We can provide a couple answers to this question. First, some poets insist that it was the Graeae, the Gorgon's sisters, who lived at Earth's perpetually dark edge. These were the rather disagreeable three sisters who were literally born as old women. They shared a single tooth and one eye amongst them. (Perseus captured and withheld this eye from them until they agreed to disclose Medusa's location.*) By this version, Perseus had no trouble at all seeing Medusa. The second answer presumes that the Gorgon island WAS perpetually dark as neither the Sun nor moon ever ventured over it. This constant darkness would have prevented the gorgons from petrifying each other. That leaves open the question as to how Perseus could have beheaded Medusa without seeing her. We know that Athena gave Perseus a highly polished shield which enabled him to follow Medusa's reflection, thus saving him from being petrified. He would have still needed a light source. It is simple to think that perhaps Athena, being a particularly clever goddess, would have endowed her shield with luminescence so as to allow Perseus to see the reflection. We also know that Athena (some say Hermes) guided Perseus' arm when Medusa came within striking distance, so Perseus wouldn't have to risk petrification at all. I hope these answers prove helpful or, at least, ha ha, illuminating. *In some versions, the gentlemanly Perseus gently handed the eye back to them after they provided him with the information he demanded. In other versions, he quite detestably tossed it in a nearby lake and invited the wretched women to "fetch it."