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."