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
Julian date:  2457659.16
              "Heavens above!"



THE DAILY ASTRONOMER
Tuesday, September 27, 2016
Pandora's Return!

 We intended to mention this before and, honestly, we probably shouldn't
mention it now, but we have set a goal for ourselves.  By or before August
4, 2017, we want to answer at least 100 -preferably 2,000- Pandora
parchments.   For those who've just jumped aboard this renegade comet
nucleus of a ride, Pandora parchments are those scraps of ancient paper on
which we inscribe all the astronomical questions we receive.  These
questions come from planetarium patrons, DA subscribers, "Radio Astronomy"
listeners, Facebook friends, 8th century wizards who are too embarrassed to
ask people in their own time period, and so forth,    We store them in a
nifty little vessel we have dubbed "Pandora's Jar," after the troublesome
lady who released all of the world's troubles, leaving only hope behind.
   We tucked this vessel away in the planetarium's dome shadows, where we
also keep the Irish King's amulet (long story),  the wind chimes that play
only UV light (longer story) and various other little trinkets we've
accumulated over our 46-year history.      Just before September 1st -when
the new school year commenced- we resolved to answer at least 100 questions
before the school year ends on August 4th.    Quite understandably, we knew
that we'd have to dig into Pandora's depths by at least September 5th to
make a good start.   Well, look at the date...ha ha!

So, without any further adieu, we return to Pandora's Jar. As we do so,
we'll number the questions to keep track of them!    Wish us lazy sods
luck, because we're starting late.


PANDORA  1:    CURVED LIGHT
*"Is distant light still believed to "curve" around a mass ? Or is that
debunked theory?"          -Shawn Dow,  Hollis, Maine*

Greetings, Shawn,
That theory is not debunked at all.  In fact, astronomers now know that
massive objects will distort their local space-time geometry. An object
that is sufficiently massive will cause light to bend around it.
Now, that we've answered the question, we should delve more deeply into the
science.

Albert Einstein's General Theory of Relativity (1915) pertained to
gravitation.    Even though the math is straight out of a 29th century
sorcery book, the basic idea is that massive objects bend space-time.
Space-time is the continuum combining the three spatial dimensions and one
time dimension.       Think of a taut rubber sheet.    Place a bowling ball
on that sheet and you will produce a small indentation around the ball.
Then, imagine rolling ball bearings across the sheet.  Those bearings
closest to the ball will be drawn toward it by the indentation.   The
indentation won't affect the more distant bearings        A massive object
such as the Sun induces a "indentation" in space-time and the planets that
revolve around it are trapped in this indentation.  One can also regard it
as a gravity well.   According to Einstein, this indentation would affect
light paths as well as massive objects.       Gravity could actually "bend"
light.


​
*The Sun's "Gravity Well."    The Sun distorts its local space-time
geometry and in so doing "traps" the planets within this well.     Here, we
see Earth at different positions along its Sun-centered orbit. (Not to
scale).     The space-time "dents" produced by massive objects affect
photons as well as massive objects.     Image by Carlos Clarivan*

Einstein's assertion that gravity resulted from space-time, itself was
dismissed as preposterous by most, as it directly contradicted Newtonian's
ideas of absolute space and time.   However, in May 1919, British
astronomer Sir Arthur Eddington (1882-1944), led an expedition to
photograph the sky during a total solar eclipse.       When an eclipse is
at totality, the stars behind the Sun become visible.     Eddington's team
photographed the sky during this eclipse and determined that the stars'
positions had been affected slightly by the Sun, just as Einsteins
predicted.   This first piece of evidence in support of General Relativity
elevated Einstein to the status of global celebrity overnight and forever
changed our view of space-time.

Throughout space astronomers see examples of massive objects bending
light.  Over vast distances, we can see examples of gravitational lensing:
how light paths are shifted around highly massive objects such as galaxies.
     A single light source can appear as multiple light sources due to this
lensing effect.  See image below.


​*A simplified example of "gravitational lensing."    Here, we see a light
source which bends around a massive object located between it and Earth.
As the light moves around this object, it appears to be two light sources.
       IMAGE: NASA/ESA*


*Whew....only 99 more Pandora parchments to go....*

*____________________________________________________________*
*FROM THE CATACOMBS OF INFINITE KNOWLEDGE*
*The Cross Overhead!*

It is admittedly difficult to discern one's directions in the night sky.
  However, it is easy to simply look directly overhead.  Tonight, mid
latitude observers will be able to peer up at the zenith and behold the
Great Northern Cross.    This star pattern comprises most of Cygnus the
Swan, a constellation within the Summer Triangle.



*​The Northern Cross.    Otherwise known as "Cygnus the Swan," the Northern
Cross looms high overhead early this evening.   Even though its brightest
star, Deneb, is par of the Summer Triangle, the Northern Cross is a
prominent celestial sight in early autumn.    Image by Bob King.*

The Northern Cross consists of a long axis of stars with a shorter axis
nearly perpendicular to it.    The Northern Cross is larger than the more
famous Southern Cross (which is only visible at latitude south of 30
degrees N.) .     The Northern Cross will remain in our eastern sky until
early winter, when it will set high in the northwestern sky at dusk.
Although Deneb is Cygnus's brightest star, the "head" star Albireo is an
exquisitely beautiful binary (double) star.  One component star is golden,
the other one is sapphire.    One can resolve this star into its member
stars even with small telescopes.   This practise, called "splitting
Albireo" is a favorite activity of many recreational astronomers.

Venture outside and seek the Northern Cross yourself.  It is easy to find
right now.   Just go out and literally look up!
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