good morning John now okay what is this
why am I doing this now why am i showing
you this very bad image you know just
because it's objectively one of the best
images ever taken in all of human
history but first when I was a kid I was
really frustrated by something we knew
where we lived in our galaxy we knew how
big the galaxy was how far away other
galaxies were but there was a pretty
simple question that no one could answer
for me how many stars are in the sky now
there's a bunch of reasons why this is a
hard question to answer first that
number is very different depending on
conditions like if it's cloudy the
number is zero if you're in the middle
of the wilderness on a clear day it is
much higher and also it's very different
depending on the equipment you're using
like if you're using your eyes or
binoculars or a space telescope and once
you start thinking about equipment then
you're not really asking how many stars
are in the sky you're asking how many
there are in the Milky Way galaxy and
now you got a a new problem now you
can't just count the stars in the Milky
Way for two reasons one if you take a
picture of it you can't see a lot of the
stars because there are these giant
clouds of gas blocking out huge sections
of the galaxy second and more
importantly there are just too many
stars John back to my image this photo
is actually two million photos taken
over ten years by the spitzer space
telescope which ended its mission this
week and let's actually move over to
some software that will allow me to zoom
in on it without crashing my computer
spitzer is an infrared telescope which
means it can see the heat of stars even
through all of those gas clouds and so
we can actually see a more unincluded
galactic core and still we can't see all
of the stars because of all the stars
that are in the way it's like a soup of
stars like bioluminescent plankton in
the waves except that every point of
light every microorganism instead is a
solar system
this view is looking through almost all
of the galaxies and because we are
taking that picture from the edge of the
Milky Way where our son is there's a lot
of galaxies to look through instead we
can also look outward through the thin
band of the galaxy that is between us
and the intergalactic void and they're
beautifully and upsettingly
we have a thinner soup but still a soup
John there are a lot of stars and if you
ask an astronomer today how many stars
there are in the Milky Way they will
tell you somewhere between 100 and 400
billion and that just seems so wrong
that's a huge range but we cannot count
so we estimate based on the galaxy's
mass and what we think the average mass
of a star is but both of those numbers
have significant wiggle room right now
and so dear child Hank of the 1980s it
is 2020 now and we still don't know how
many stars there are in the Milky Way
galaxy but you can get an idea of what
hundreds of billions of stars look like
from this image that took decades of
work to create and that's pretty cool
John I'll see you on Tuesday thank you
to all the people who worked on the
spitzer space telescope project over the
years this galactic map was of course
only one of the amazing achievements of
that project it was only a hundred years
ago that we were arguing about whether
or not the Milky Way was the entire
universe or whether there were other
galaxies out there
the person who finally proved those
other galaxies were there and did exist
his name was Edwin Hubble and the guy
who first conceived of the idea of
putting telescopes in outer space and
was a huge champion of the hubble space
telescope while his name was Lyman
strong Spitzer