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
July the 21st of 2020.
While it is titled Iron
in the Butterfly Nebula.
So what do we see here?
Well, this is an example of
a planetary nebula, which
gives the shape of it perhaps
a butterfly central portion
and then two great
wings stretching out.
Of course, those wings
cover several light years
worth of space.
So it spreads out over
much larger of course
than any earthbound butterfly.
Now a planetary nebula is
what happens when a star much
like our own sun dies.
The central star left at
the center is extremely hot
- hundreds of
thousands of degrees
and is actually the core
remnant of the star left behind.
The outer layers have been
expelled out into space.
And we see them in the pattern
that gives us the butterfly
shape that we see here.
So those are the outer layers
as they stretch out into space.
Recycling material back in to
the interstellar medium to help
form the next
generation of stars.
Now here, we're actually looking
at light of a specific element.
So it's not a true color image.
This is not what the
nebula looks like.
But we're highlighting
emissions of iron.
So we're looking at
where the iron is present
even though this nebula
the vast majority of it
will still be made up of
hydrogen. Hydrogen is the most
common element in the universe
and with very few exceptions
almost everything in the
universe is made primarily
of hydrogen. So this
whole nebula is hydrogen.
And that means that's because
it is the outer layers
of the star that has expelled.
This material.
So these are the outer
layers of the star
and the core has condensed
down to something
about the size of the earth.
And it's what we call a
white dwarf star is what
will end up being left behind.
There Sol the Hubble
Space Telescope
image that we're
looking at today
gets a chance to show all of
the details of that nebula
all of the clumps of material
as they expand outward
into space in this very
short lived version of a part
of stuff stellar lifetime,
a star like our sun
can live for 10 billion years.
And after that, it has
another billion or so years
as it goes through other stages.
But this stage only lasts
tens of thousands of years.
So it's very short by
comparison to the other stages
and of course, we only get
to see those stars that
happen to be going through
that stage at this moment,
such as the butterfly nebula
that we see here today.
So that was our picture of the
day for July the 14th of 2020.
It was titled Iron in
the Butterfly Nebula.
We'll be back again tomorrow
for the next picture.
So until then, have a
great day, everyone,
and I will see you in class.
