THE SOUTHWORTH PLANETARIUM
207-780-4249   www.usm.maine.edu/planet
<http://www.google.com/url?q=http%3A%2F%2Fwww.usm.maine.edu%2Fplanet&sa=D&sntz=1&usg=AFQjCNHulkHuLP13bOG2PkNrPazsGWFs2A>
70 Falmouth Street   Portland, Maine 04103
43.6667° N                   70.2667° W
Altitude:  10 feet below sea level
Founded January 1970
Julian date: 2458784.16
2019-2020:  XL
               "Find a way or make one."
               -Robert Peary, co-discoverer of the North Pole and Portland
native



THE DAILY ASTRONOMER
Monday, October 28, 2019
The Blue Snowball Nebula

[image: NGC_7662_"Blue_Snowball".jpg]
NGC 7662: *The Blue Snowball Nebula.  *

The night sky is fiercely alive with the most vibrant colors!    Our human
view of the night sky, well, isn't.   As our eyes are not developed to
perceive colors at low light levels, the firmament often seems devoid of
colors, save for the rosy fingered dawns and elemental dusk fires.

Today's excursion into the Universe brings us to the Blue Snowball Nebula,
a beguilingly beautiful planetary nebula of indeterminate distance within
the constellation Andromeda the Chained Princess. An expanding shell of
gases envelope a white dwarf stellar remnant with a surface temperature
exceeding 75,000 degrees.     At apparent magnitude 8.6, the Blue Snowball
Nebula is more than six times fainter than the dimmest naked eye star.
However, observers with a small recreational telescope can observe it as a
star smeared by a whisper of nebulosity.     Through moderate sized
telescopes (6" aperture), one can observe a blush tint.  Through larger
scopes, one can detect a hint of the color variation that is so pronounced
in the above image.

Not only does the Blue Snowball Nebula provide another example of the
myriad masterpieces adorning the depths of the heavens.  It also
foreshadows the Sun's ultimate fate: in the remote future when it exhausts
its core fuel reserves and concludes its life cycle.    Presently, the Sun
generates copious energy through core thermonuclear fusion reactions:
specifically, the Sun is fusing hydrogen into helium and in the process
transmuting a minute amount of the hydrogen into energy.    The energy
pressure exerted outward precisely counterbalances the unrelenting
gravitational contraction to lend the star its stability: a state called
"hydrostatic equilibrium."  Although the Sun will deplete its core hydrogen
reserves in about five billion years, its core temperature will ultimately
increase so as to fuse the helium into carbon.   Prior to the initiation of
these helium fusion reactions, its outer layers will expand dramatically,
causing the Sun to become  a red giant.   The Sun will contract to a
smaller volume when the helium reactions commence.   Once the Sun exhausts
its core helium, it will not be able to fuse carbon as it lacks the matter
necessary to induce pressures and temperatures required for this more
advanced fusion reaction.
The Sun will expel its outer layers into space, leaving behind an ultra hot
planet-sized remnant called a white dwarf.     The outer layer will form a
planetary nebula.    This nebula is not so named because of the size of its
dwarf, but because a rather obscure French astronomer ,Antoine Darquier de
Pellepoix, observed the Ring Nebula in 1779 and described it as being
similar to Jupiter in size and appearance.  William Herschel also noted the
nebula's planet-like appearance, henee the continued use of the term
"planetary nebula" indicating the gaseous remains of a solar-mass star.

[image: Léonard_Defrance_Antoine_Darquier_de_Pellepoix.jpg]
*Antoine Darquier de Pellepoix*
(1718-1802)
The French astronomer who coined the
term "planetary nebula"

The white dwarf star in the nebula's center will slowly cool through the
highly inefficient radiative cooling process. (Convection cools hot
material much more quickly.)   After billions of years, the dwarf will fade
to black as it finally releases its trapped heat energy into space.   The
white dwarf will persist for so long despite the absence of fusion
reactions due to "electron degeneracy."  Electrons within the dwarf will
repel each other with sufficient force to counteract the gravitational
contraction pushing inward.

The constellation Andromeda ascends through the eastern evening sky
tonight.  Well concealed within the constrained princess lurks a gorgeous
azure blue nebula formed by the material expulsion of a distant star.
Eventually, the heated gases will cool and dissipate, leaving an isolated
stellar remnant.      By seeing the Blue Snowball Nebula we're seeing a
preview of our own star's demise.  It makes one wonder how many beings will
observe that nebula about 6.5 billion years from now and how enchantingly
beautiful the Sun's death throes will become.


TO SUBSCRIBE TO OR UNSUBSCRIBE FROM THE "DAILY ASTRONOMER" LIST-SERVE:
http://lists.maine.edu/cgi/wa?SUBED1=DAILY-ASTRONOMER&A=1
<http://www.google.com/url?q=http%3A%2F%2Flists.maine.edu%2Fcgi%2Fwa%3FSUBED1%3DDAILY-ASTRONOMER%26A%3D1&sa=D&sntz=1&usg=AFQjCNFULbYWhPaagSdTTFqjXHF4ALIV8A>