Greetings and welcome to the
Introduction to Astronomy.
One of the things that I like
to do in each of my introductory
astronomy classes is to begin
the class with the astronomy
picture of the day from
the NASA website that is
APOD.NASA.GOV/APOD.
And today's picture for
September the 29th of 2019.
Well, it is titled MyCn 18: The
Engraved Hourglass Planetary
Nebula.
So what do we see here?
Well, this is an
example of what we
do call a planetary
nebula, which
has nothing to do with
planets, but is actually
the end state of a star
much like our own sun.
So this is the kind
of thing that our sun
will become when it
exhausts its fuel
and reaches the end of its life
in about five billion years.
And what happens is
that the outer layers
continue to expand and
get larger and larger.
So our sun will
grow in size to fill
the entire inner solar system.
As that happens, the inner
core will condense down
to something about
the size of the Earth.
Now the inner core will still
contain the vast majority
of the mass of the object.
And that will become what
we call a white dwarf star
very compact star with all
the atoms pressed together
as close as they possibly can.
The outer layers will
become larger and larger.
As it grows and will eventually
become detached from the star
itself.
So the star will
separate into two pieces.
And that's what we see here a
central core as the white dwarf
star and then the outer
layers as material has
been expelled out into space.
Now we can see, there is
a very big symmetry here
in the nebula at the
top and bottom portions
seem almost exactly the
same and whether that
is a matter of
perspective or something
to do with the ejection process
is a really good question
as to how this happens.
It's not something
that is completely
understood at this
time how this works,
how we can form a power
of planetary nebula
actually forms.
But we can see what either
are multiple ejections which
look very similar,
which is interesting.
And then maybe something
even more recent
towards the central portion.
Now this is a relatively
young planetary nebula
so this is something that
has happened only recently,
though not something
that's been around
for many millions of years.
And in fact, a planetary
nebula stage of a star
is a very short phase lasting
only tens of thousands
of years, which compared to a
billion year lifespan of stars
like this or many
billion year life span
is just a very short time
just the blink of an eye
that we get to see this.
So it's only when we happen
to catch it at that stage
that we get to see and get to
study this with images as this
was taken with the
Hubble Space Telescope
to try to better
understand this object
and to give us a better
understanding of what
might happen to our sun
in the distant future.
So that was our picture of
the day for September the 29th
of 2019.
It was titled MyCn 18: The
Engraved Hourglass Planetary
Nebula.
We'll be back again tomorrow
for the next picture previewed
to be Orion Treed so we'll see
what that is about tomorrow.
And until then have a
great day, everyone.
And I will see you in class.
