*THE SOUTHWORTH PLANETARIUM*




*207-780-4249 <207-780-4249>       www.usm.maine.edu/planet
<http://www.usm.maine.edu/planet> 70 Falmouth Street  Portland, Maine 04103
43.6667° N,                    70.2667° W Founded January 1970*

*              "Whatever you can do, or dream you can, begin it. Boldness
has genius, power, and magic in it."  -W.H. Murray* (1913-1999)




*THE DAILY ASTRONOMER*

*Tuesday, April 26, 2016*

*Darker Pandora*


*Last week during our Pandora fest, we found to our horror that we had
neglected two questions tucked deep within the dark depths of Pandora's
jar.  Ironically, both of them pertain to darkness, at least in some
respect.       To those subscribers who posted these queries and then
thought we were neglecting them, we offer our sincerest apologies.      *




* "What would we on Earth experience if the sun were to 'shut off'
instantaneously? i know this is a scary concept, but i find it
fascinating."*

*-Annie A, Asheville, NC*


*Agreed.  That concept is rather scary.  Just to allay anybody's concerns,
we are confident that the Sun will remain active and highly energetic for
billions of years to come.  However. we'll pretend that the Sun suddenly
"shuts off" for whatever reason.   What would we experience?*

*Well, for the first 8.3 minutes or so, we wouldn't experience much of a
change because the Sun is about 8.3 light minutes away.     About 8.3
minutes after the snap off, the Sun would appear to vanish.    We would
have instantaneous night fall on every part of Earth.     No twilight would
precede the darkness because twilight is caused by atmospheric light
refraction of the Sun when it is below, but within 18 degrees of, the
horizon.    In this scenario, the light source, itself, vanishes. *



*We would not die at once.    After all, we don't all die after each
sunset. *


*Our planet would rapidly cool as its main energy source would no longer be
imparting heat and light onto it.   The lakes and ponds would solidify and
the air would become much colder.     (Curiously. geothermal heat would
still provide some heat to the oceans, which, according to one estimate,
would require one million years to freeze solid!)      *



*Humans all over the globe would frantically try to remain warm with
conventional heat sources.   However, the real problem would involve the
ecosystem.  The photosynthetic process would be curtailed by the lack of
solar energy.     Plant life all over the globe would perish, disrupting
the symbiotic oxygen-carbon dioxide exchange that sustains life on this
planet.   Moreover, the atmosphere, itself, would eventually freeze out of
the sky and settle on the ground.   However, by that time, we would have
all died by hypothermia or slow suffocation. *


*As for Earth, itself:*


*If the Sun remains in place, but just goes dark, Earth and the other
planets will continue to revolve around it.     The remains of the Sun
would appear as just a dark circle migrating across the sky.  We would only
"see" that circle by observing the half-degree patch that was devoid of
stars. *



*If the Sun, itself, vanishes, then Earth and the other planets will start
traveling along a path tangential to their orbits.    All the planets will
hurl through interstellar space like the renegade worlds we discussed
yesterday.     The constellation shapes won't appear to change much even
over thousands of years.  Only after great periods of times would even
these pattern become distorted, a combined effect of the stars' proper
motions and Earth's changing position in the galaxy.*



*"How do we know dark matter exists if we can't see it?"*

*-Bruce M, Cumberland, ME*



*Here, we harken back to an astronomical adage "If it isn't observed, it is
inferred."*


* Dark matter refers to material that doesn't emit electromagnetic
radiation.  Astronomers study celestial objects by studying the EM
radiation they exude into the Universe.   They detect dark matter by
observing how it affects visible matter in its vicinity.    For instance.
astronomers can measure the speeds of stars as they describe orbits through
galaxies.     The amount of matter within a galaxy determines the stellar
velocities.  The greater the galaxy's mass, the faster the stellar
motions.**





*This rotation curve shows the discrepancy between the expected and
observed velocity of stars within the galaxy M33.   Except for the region
immediately surrounding the galactic nucleus, the revolution speed of stars
should decrease substantially with decreasing distance from the nucleus.
However, the speeds actually increase.    This unexpected increase
indicates the presence of unseen matter, the gravitational influence of
which is causing this increase in stellar velocities. *

*For this reason, stellar velocity should also decrease with increasing
distance from the nucleus. *


*Observations of stars within galaxies, such as, for example, M33, have
shown that the velocities of stars don't decrease as expected. (Refer to
the graphic above.)   Also, the motions of all the stars within the
galaxies are far faster than expected.  If the only material in the
galaxies were visible, then the stars would be moving much more
slowly.      Based on this velocities, astronomers assume that galaxies are
predominantly dark matter, comprising, perhaps, as much as ninety percent
of the entire mass.  *

*Astronomers cannot see dark matter, but they know it exists because they
know how it influences the matter we can see.    The question as to the
nature of dark matter remains unresolved. *




**Mass and motions are directly related.  If, for example, the Sun's mass
increased, Earth's orbital velocity would also increase.   *