Happy 200th episode, everyone, 200 down and at least 200 more to go.

And to celebrate our likely unending quest into complete knowledge of time and space, I wanted

to recount my most favorite outstanding questions in modern astronomy.

Like last time, this will be a list of five top mysteries in astronomy. Like last time,

we're only going to focus on astronomy. You know, maybe for the 300th episode, we'll do this again,

but for physics. And we're going to have less preamble today because I already said most of it last

time, but just in case you're not a fan of the biggest discoveries of the past and are more

of a forward-thinking kind of person, here's how to get on my list.

Number one, breadth.

Many people are working on the same problem from a bunch of different angles.

There are lots of problems out there, but not every problem captures the imagination and curiosity and interest of a large fraction of the astronomical community.

Number two, depth. This is actually a difficult problem and requires a lot of different people taking different approaches, requires

observations and theory, and lots of just sitting around talking, trying to figure it out.

Number three, potential. Well, not guaranteed. Solving this

mystery will probably lead to a radical changing of the way we understand the universe,

and even making progress itself, will have a substantial impact, even if it all leads to nothing,

because the tools and techniques

and insights we gain just to try to tackle the problem will give us lots of cool, new ideas

about the universe. And lastly, neatness, not orderliness, but how nifty, interesting, or intriguing

the problem is based solely on my own

sensibilities. And so given these categories, we can already move on to our honorable mentions

today, which go to Galactic Evolution, Star and Planetary Formation, Solar Weather, and everything related to dust. Unlike the last

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