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
February the 15th of 2020.
Well, it is titled
Carina Nebula Close Up.
So what do we see here?
Well, this is the
great Carina nebula -
a very large star forming region
and in fact, one of the largest
star forming regions
within our galaxy.
Star forming regions are
concentrations of gas and dust.
And while there is a
lot of gas and dust
throughout the galaxy
when it is concentrated
in the star forming
region there there's
an energy source that
causes it to be illuminated
and that is the energy and
the ultraviolet radiation
from all of the hot young
stars that have formed.
And those will excite the
gas and cause it to glow.
So while there is
hydrogen gas elsewhere
in the galaxy when it is here
in a star forming region,
we can actually see it.
And we can see a lot
of that hydrogen gas
glowing very brightly here.
But we also see some
dark dusty areas.
And you can see a number
of dark kots here.
And those are concentrated
regions of dust and regions
where star formation
is just beginning.
So in the earliest
stages of star formation
a large cloud of gas and
dust will begin to collapse.
And if the dust is
dense enough, it'll
block out the light
from behind it
and keep us from being able
to see into that cloud.
It's sort of like a
cocoon around the star.
So we are unable
to see into that
with visible light
ordinary light
that we're used to
looking at will not
penetrate through that dust.
It's like looking
through a wall.
However, if we look at it
in the infrared portion
of the spectrum than we would
be able to see into those.
And that's one of
the ways we can
study some of the very earliest
stages of star formation
as the process continues.
More stars will
pop out and we'll
begin to excite
the gas around them
and will cause the gas
around them to glow.
Now, one of the
very prominent stars
here is the star Eta Carinae.
And that is off towards
the lower left here,
and that is a incredibly massive
star over 100 times the mass
of our sun and about towards
the limit to what we believe
a star can actually achieve.
So there is actually a limit to
how big a star can be because
of the intense rate
of nuclear reactions
in the center will eventually
create so much radiation
pressure it'll push the
star apart and keep any more
material from adding to it.
So it will be strong enough to
overcome gravity and push some
of that outer material
away, keeping the star
from growing any larger.
It is also the type of star that
is expected to go supernova.
And if we look at this
star we can even look at it
and have looked at
it before up close.
This is the type of star we
would watch for and expect
sometime in the near
future to explode
and whether that be next
week, next year or 100 years
from now, it is still
a star that astronomers
will be watching as
there seems to have
been a large number of
supernovae in this area.
And of course, some
of them could be seen.
Others could be completely
hidden by the dust.
There is that much
material there
that it can completely block
out light from around it.
So we need to use other
things such as X-ray.
X-ray emissions to be able to
see many of those supernovae.
So here we get our image
of the Carina nebula.
So that was our picture of
the day for February the 15th
of 2020.
It was titled Carina
Nebula Close Up.
We'll be back again tomorrow
for the next picture previewed
to be Planetary Nebula Portrait.
So we'll see what that
is about tomorrow.
And until then have a
great day, everyone.
And I will see you in class.
