THE USM SOUTHWORTH PLANETARIUM
207-780-4249     www.usm.maine.edu/planet
70 Falmouth Street     Portland, Maine  04103
43.6667° N                   70.2667° W
Altitude:   10 feet below sea level
Founded January 1970
Julian date:  2458660.5
          "If you're in a spaceship traveling at the speed of light, and
you turn on the headlights, does anything happen?"
                               -Stephen Wright

THE DAILY ASTRONOMER
Wednesday, June 26, 2019
Apple Core Nebula


We call it the "Butterfly analogy."   Perhaps you've heard us discuss it
before and, if so, our apologies for the repetition.      Envision a
butterfly scientist whose aim is to understand the human being.   The
butterfly has the profound disadvantage of a fleeting life span, far more
brief than the human life cycle.   So, one might wonder how our butterfly
scientist could hope to fathom a specimen that is virtually immortal in
comparison.    Our little lepidoptera can't linger about observing the
human mature from infancy to the convalescent home.     However, the
butterfly can observe humans in various development stages:  he can observe
the baby, the codger, the thirtysomething woman; the middle-aged man; the
teenager and young adult.     Were this butterfly a clever sort, he could
piece together the evidence to form a human life cycle sequence.  The human
is born a codger, shrinks down to an infant, expands into adulthood, alters
its gender; and then blossoms into a teenager.  (Being clever doesn't mean
one is always correct.)

The astronomer is like the butterfly.   We humans are ephemeral twerps
relative to the cosmos.   The Universe is billions of years old and will
likely exist for trillions of more years, if not longer.  Even a century is
spark-quick by comparison.  So, how can astronomers know so much about the
Universe?*   Well, first of all,  Earth has been blessed with more than one
astronomer and so those alive today have benefited greatly from the work of
preceding generations.   Also, we can observe stars and galaxies in various
stages.     We can observe star birth in regions such as the Orion Nebula
and we can watch a star's death throes in objects such as the Apple Core
Nebula, also known as the Dumbbell Nebula.

[image: 2015-08-24_55db0065714c5_M27-RHaGOIIIBOIII-MlC-PicProc-NVC-1000.jpg]
The *Apple Core *or Dumbbell Nebula:  a planetary nebula "within" the
constellation Vulpecula the Fox.

Discovered by 18th century French astronomer Charles Messier, the Dumbbell
is a planetary nebula, one formed when a solar-mass star ends its life
cycle.   The star expels a rapidly expanding gaseous shell and leaves a
highly dense white dwarf in its center.      English astronomer William
Herschel coined the strange term "planetary nebula" for these objects as
they resemble disc-like planets in the telescope.   We know that they have
no association with planets, but the term remains.

Located 1,360 light years away in the constellation Vulpecula,* the Apple
Core Nebula is quite luminous, exhibiting an array of different colors.
 The copious ultraviolet radiation excites the nearby gas atoms, causing
them to re-emit the absorbed photons as visible light.   When observed
telescopically, the nebula's color are rather muted.  Only when captured
through a long-time exposure image will the nebula's vibrant hues and
filamentary structures become visible.

The nebula spans a 2.5 light year diameter and expands at 31 kilometers per
second (69,230 miles per hour).    Observations of this expansion velocity,
which isn't constant, have enabled astronomers to estimate its age between
9,400 - 13,000 years, or the time the star pushed its gases into outer
space.     Seeing planetary nebulae such as the Apple Core or the Ring
Nebula in Lyra the Harp gives us a view of the future Sun. Sol will
eventually ends its life as a planetary nebula and white dwarf core.
Fortunately, this transformation won't occur for billions of years.  That
we can see it happen to stars now enables us to understand the Sun's fate
in the remote future.


*Let's have a moment to reflect on this misleading sentence.   One would
think that the constellation Vulpecula (the fox) occupies a specific
region, like a cube, and that the Apple Core Nebula sits neatly inside it.
  Actually, the stars comprising the Vulpecula constellation are not
physically connected, but just happen to be positioned along the same
sight-line.    The Apple Core Nebula is also in the same direction, making
it appear to be "inside" the Vulpecula constellation.