THE LIFE OF A STAR LIKE THE SUN

The Sun generates all of its heat in its core. This heat both warms the
Earth and prevents gravity from forcing the Sun to undergo a catastrophic
gravitational collapse. The fuel which supplies the heat is hydrogen.
Hydrogen nuclei are converted to helium as heat is released.

In five billion years the hydrogen fuel will have been used up. Gravity
will force the spent core, now almost pure helium, to shrink, compress, and
become even hotter than at present. The high temperatures will eventually
ignite the helium ashes. The result is a formation of carbon nuclei and even more heat. The
"second wind" of heat release will be furious, increasing the light emitted
from the future Sun's surface by a thousand times. Meanwhile, the same heat
will cause the outer layers of the present Sun to expand and form a huge
"red giant".

The red giant is so bloated that Mercury and Venus will find themselves
orbiting inside of it. Imagine daytime on the Earth when this happens.
Sunrises and sunsets will take hours, thanks to the huge apparent diameter
of the swelled Sun. At noon the huge bright red Sun will fill half the sky.
The view won't be very different than that within a pottery kiln. The oceans will
boil and evaporate into space, along with the atmosphere. The intense
radiant heat will transform the Earth's surface to a thick layer of pottery. In all,
a biblical view of hell.

As stellar time goes, the helium won't last long - certainly less than a
mere few hundred million years. With its helium transformed into unburnable
carbon, the solar core shrinks suddenly (a few thousand years) until just
over half the mass of the present Sun is packed into a hot (million degree),
dense (a ton per teaspoon) ball the size of the Earth. This amazing stellar
remnant is called a white dwarf.

The remnant's fuel reserves are now finally gone. Its shrunken stellar core
is now entering retirement. Even so, one large final fling lies ahead for
this star.

The story shifts from the dying core to the star's distended outer layers.
The core, their underlying foundation, now has all but imploded. The outer
layers of the Sun fall inward toward the core. But the base material ignites
on the way in, causing the outer surfaces to bounce and vibrate. Eventually
the outer 40% of the Sun's mass will be spasmically "coughed" into space,
floating outward through the solar system and beyond in a concetric set of
spherical bubbles. Seen from far away, these may eventually blend together
into a gigantic stellar "halo". As the outer layers are flung outward
increasingly deeper and deeper layers of the Sun become exposed as its
outermost surface, like peeling an onion.

When the process ends, the former core of the Sun emerges through its
exapnding veil of ejected material as a white dwarf. The highly energetic
forms of light emitted by the hot white dwarf interact with the electrons
attached to the atoms in the gas cloud, resulting in a colorful nebula much
like the thousand planetary nebulae that have been catalogued already. The
striking symmetries of these objects have led to an array of popular names
such as the "Cat's Eye", "Ring", "Eskimo", "Horsehead", and
"Blue Snowball" nebulae.

(Nebula Images Below)

IMAGINE THE VIEW!

Here on Earth, we'll feel the wind of the ejected gasses sweeping past,
slowly at first (a mere 5 miles per second!), and then picking up speed as
the spasms continue (eventuially to reach 1000 miles per second!!) The
remnant Sun will rise as a dot of intense light, no larger than Venus, more
brilliant than 100 present Suns, and an intensely hot blue-white color
hotter than any welder's torch. Light from the fiendish blue "pinprick" will
braise the Earth and tear apart its surface molecules and atoms. A new but
very thin "atmosphere" of free electrons will form as the Earth's surface
turns to dust.

Here's what some survivor will observe in the night sky.

In addition to stars,the sky will be aflame with the whispy, colorful shapes of the nebula of ejected
solar material. This spectacular show will last a few thousand years as the
ejected gasses merge into the interstellar medium from which new generations
of stars will form.

Imagine that we lived, not for a hundred years, but for a hundred million.
As we viewed our home galaxy, the Milky Way, we would see these "planetary",
or ejection nebulae flaring and fading all the time, about one per Earth
year, much as the flashes of cameras at a sports stadium at night. At any
given instant more than 10,000 nebulae are visible in some stage of their
evolution. (Once per century or two a blinding supernova would appear for a
week or two, like a powerful firecarcker.)

Planetary nebulae make the Milky Way come alive. From afar the Milky Way
would resemble a scintillating galactic Christmas tree. A red flash appears
here, and another there, as planetary nebulae form. For a few thousand years
each nebula brightens and turns from red to green. Finally, after 10,000
years, the growing nebula will expand and fade into the background of
galactic gas, as does air from a popped balloon. Each nebula leaves behind a
tiny blue white dwarf. Over the course of billions of years, the "white"
dwarves fade to a dull red ember.

The Hertzsprung-Russell Diagram

Learn about the H-R Diagram

Interactive Hertzsprung-Russell

Note: Zero degrees Kelvin is "Absolute Zero," or the temperature at which all matter stops moving.

Note: Zero degrees Kelvin is equavalent to -272 degrees Celsius.

Note: "Star Color" and "Surface Temperature" are related.

Note: "Luminosity" (brightness) and "Solar Radius" (size) are related.

Below: Winter Circle (note star color):

Capella is yellow. Aldebaran is orange. Betelgeuse is red. Rigel is blue. Sirius is blue-white.

Planetary Nebulae

The following credited to: Planetary Nebula Website

OVERVIEW

95% of all stars that we see in our own galaxy, the Milky Way, will
ultimately become "planetary nebulae". This includes the Sun.

Much as a butterfly emerges when its chrysalis is ejected, planetary nebulae
are formed when a red giant star ejectes its outer layers as clouds of
luminescent gas, revealing the dense, hot, and tiny white dwarf star at its
core.

The other 5% of stars -- that is, those born with masses more than eight
times (8x) larger than our Sun -- end their lives as supernovae.

One final note: the name "planetary nebula" is a misnomer. The name arose
over a century ago when early astronomers looking through small and
poor-quality telescopes saw these objects as compact, round, green-colored
objects that reminded them of the view of Uranus.

However, "planetary nebulae" are not made of planets, and no planets are
visible within them.

Rather, they are the gaseous and dusty material
expelled by a dying star.

A far better name for these
objects would be "ejection nebulae."

Think of ejection nebulae as a cloud of
smoke which esacpes from a burning log as it collapses and crumbles into
embers.

THE REVOLUTION STARTED BY IMAGES FROM THE HUBBLE SPACE TELESCOPE

Above: Planetary Nebula and Companion Binary Star

Hubble Space Telescope images are generating some very creative ideas about Planetary Nebulae.

One example is that a nearby companion star, or perhaps a large
planet, becomes engulfed by the expanding, dying star. The star or planet
may just find itself inside the star or close to its edge. The gravitational
forces exerted by the companion act like an eggbeater, tossing out the
loosely outer layers of the giant star into an equatorial disk. Awesome!

~Planetary Nebula Photo Gallery~

Above: The Eagle Nebula

Click here: Nebula Images

Click here: Orion Nebula

Above: Horsehead Nebula

Above: Rotten Egg Nebula

Above and Below: Cat's Eye Nebula