Hey, so, we spent a week looking at main sequence
stars and we can apply really fun and exciting thinking and observation to
learn a lot about them. That's 90% of the stars.
We want to know about the others and one of the things that main sequence stars
taughts us is that they're not eternal, they burn out.
So if we see any they must be forming, if we can ask what happened where they came
from, how it is that they formed, and what happens when they are no longer able
to be main sequence stars. What happens to a star when its done,
that'll be the topic of this week stellar evolution.
The challenge that faces us when trying to understand star evolution is that
stars evolve, but very slowly. The time scale for the sun's evolution is
tens of billions of years. We do not get to watch a star evolve.
we get a snapshot of the universe as it is now, and so we will need, again, to
apply both painstaking observation and modeling and understanding of the science
to pick piece together a picture of how stars evolve.
I spoke about sort of population studies as the realm of sociologists, I think
last week. probably a better analogy is the one I
quoted on the title slide due to the famous British astronomer Sir William
Herschel, who liken an astronomer to someone
wandering through a beautiful garden and trying to understand by looking at the
plants, how it is that they developed and evolved and developed and grow and
you can relate if you wish the fully grown redwood to a sapling, even though,
no living biologist has seen a the redwood sapling grow into a 4,000
year old mature tree. We know enough about the way plants work
to relate the two. And we have to learn enough about the way
stars work to make the same observations about stars.
one of the laboratories that we have to do this is star clusters.
Clusters are, remember, are formed when a cloud starts collapsing.
That means all of the stars in a cluster formed at the same time,
comparing the snapshot that different clusters give us at different times since
they were created allows us to compare what the status is of different stars.
All the different stars in a cluster, when they are the same age and this gives
us different snapshots of the population and this will be an important tool in
understanding what we know about star evolution.
So the plan for the week is start by talking about how stars form.
We'll talk about the pre-main sequence aspect of solar evolution.
We'll skip over the rather boring sedate main sequence and talk about all the
exciting things that happen after the main sequence.
We'll mention giants, and super giants, and dwarves, and
remnants, and all kinds of exciting explosions.
And, in the process we will have filled out the HR Diagram, explained all of the
things that are not main sequence stars that we have found, and piece them
together in an interesting pattern. We will discover many new phenomena and
some new physics that will be required to understand them.
More this week than in any previous week, we will be addressing questions to which
the answers is not known not just to me but to mankind,
and so, there will be a lot of well some people think this and some people think
that. I think that's very exciting.
we will be acquiring more steps on our construction of the Cosmic Distance
Ladder:, ways to measure larger and larger distances to add more and more of
the universe to our 3D picture of things to which we can determine the distance.
We will not be discussing this week the end to, despite the fact that clusters
play an important role in what we talk about,
the dynamics of the formation of clusters, the molecular clouds the come
from and the dynamics of how clusters evolve
are going to be relegated to our study of galaxies, since those are structures
above stars we will relegate them to galactic studies. Although as some of the
aspects of the physics we study will be require relativistic physics and we will
skip that because relativity will be the topic for next week and I hope you
enjoyed this one.