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 23rd of 2019.
Well, it is titled NGC
1499: The California Nebula.
So what do we see here?
Well, this is an example
of an emission nebula.
And this one is known
by a couple of names.
First of all, a catalog
designation of NGC 1499
for the New General Catalog
of objects that are not stars.
So essentially, a
catalog to thousands
of objects that were not
stars they could be galaxies,
they could be star clusters
they could be nebulae
as was the case here.
Now the original
work on this catalog
was done back in the late 1800s
- the thing we have to realize
is that at that time, we really
didn't completely understand
what all of these objects were.
We could tell that
they were different,
but we really didn't
have the understanding
that a spiral
nebula, which we now
call a spiral galaxy was
really another galaxy much
like our own Milky
Way, that was something
that realization
would not would still
be a number of decades away.
So anything that
didn't look like a star
was kind of grouped
into this catalog.
So we'll find all sorts of
objects there from again
star clusters to nebulae such as
the one we're looking at today
to even other galaxies.
Now as I said, this is an
example of an emission nebula.
An emission nebula
occurs because the gas
is emitting light.
And that is caused by
the ultraviolet radiation
from a hot star nearby.
So the bright blue
star near this image
is actually emitting a lot
of ultraviolet radiation
that excites the atoms
- causes them to glow.
What it does is it
strips the electrons off
of the hydrogen atoms.
A hydrogen atom consists of
one proton and one electron.
So when you strip the
electron off all that's left
is a proton.
Now the protons
can't do too much.
But eventually over time they
will recombine with an electron
and as that happens, it will
jump through various energy
levels and each of those gives
off a very specific wavelength
of light for hydrogen
one of the primary ones
in the visible portion
of the spectrum is red.
So we get this very
distinct red light
that we see we in hydrogen
of atoms are re combining.
So it's a continuing process.
Hydrogen atoms are being
stripped of their electrons
and other hydrogen
atoms are recombining
with those electrons,
giving us this red glow
and giving it - and happening
the way the material is
distributed giving it a shape
that has a vague resemblance
to the state of California.
Now it's not only
an emission nebula
we can also see some portions
of dark nebula there as well,
especially towards
the left hand side
and those darker areas
are denser concentrations
of material with a
light is blocked out
and could likely be
regions of star formation.
So quite a bit that we get
to see in our image today.
Of course, we see
some of the stars
we get to see the
California nebula
and some dark nebulae a dark
portions of a nebula as well.
So that was our picture of
the day for August the 23rd
of 2019.
It was titled NGC 1499:
The California Nebula.
We'll be back again tomorrow
for the next picture previewed
to be Millions of Stars.
So we'll see what that
is about tomorrow.
And until then have a
great day, everyone.
And I will see you in class.
