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
August the 26th of 2019.
Well, it is titled NGC 2170:
Angel Nebula Still Life.
So what do we see here?
Well, here is a
cosmic painting, not
a literal painting a
photograph an image of what
is known as the Angel Nebula.
Now the Angel Nebula is not
just a single type of nebula
but like many star
forming regions
actually is composed of
many other different types
of nebulae.
So we see, for example
reflection nebulae
the blue color around some
of the bright hot stars,
which is dusty
material reflecting
the light from those stars.
And it looks blue for
a couple of reasons.
First of all, those stars are
emitting primarily blue light,
but also the dust
particles are much better
at scattering the blue
light blue light ends up
being scattered
around by the dust
particles and red light
passes through better.
So we tend to see them as blue.
So we see that those types
of nebulae around some
of the brighter stars here.
We also see emission nebulae
emission nebulae in red
is glowing hydrogen gas.
Now most of what
we see in astronomy
and we look out at stars and
galaxies is all hydrogen.
90% of the atoms in the
universe are hydrogen atoms.
So when we look at something.
For example, stars,
galaxies they're
mostly made up of hydrogen.
Even within our own solar system
except for the
solid, rocky planets
most of the objects, the
large planets and the sun
are primarily made
up of hydrogen.
So hydrogen when it glows
is gives off a red color.
So when it's excited
by these hot stars
it glows in a red color.
And we also see dark
and dusty nebulae here.
So some of the dark dusty
areas towards the center
of this frame while they are
dusty areas areas where there
is higher concentration
of material
and therefore light from
behind is blocked out.
So they are not an
absence of material,
but the presence of
extra material in there
that is blocking out the
light from behind these
and not allowing us to be
able to see through it.
So here we have,
again, a very nice star
forming region, which can
come across as a painting
although as noted
in the description,
the canvas for this painting
at the estimated distance
for this cloud would be
60 light years across.
So quite an immense painting
and an astronomical one
in more than one way.
So that was our picture of
the day for August the 26th
of 2019.
It was titled NGC 2170:
Angel Nebula Still Life.
We'll be back again tomorrow
for the next picture previewed
to be Antares Orange.
So we'll see what that
is about tomorrow.
And until then have a
great day, everyone.
And I will see you in class.
