Wendy Freedman

So dust, just like here, if you're looking at a mountain far away and a dust storm blows up, you look at the sun or you look at the mountain, the sun's going to get redder and fainter.

Same thing happens if there's a fire, right, if you've seen a red sun.

That's what happens when we're looking at these cepheids through the dust.

They get redder and dimmer.

And so if they look dimmer, you're going to say, oh, this is farther away.

If you haven't corrected for it, no matter how many times you make the measurement, you're still going to have an error.

So there's this distinction between precision and accuracy.

And if you only use one method, if you're only using the cepheids, you're not going to be able to tell what the systematics are.

So you have to use, you know, that's my strong feeling.

That's what drives my research is you have to do this in more than one way.

That's exactly right.

Yes.

And I think certainly historically, that's what we've seen in these measurements.

It's always the systematics that come back to bite you.

And often they're unknown systematics.

We know about the dust now.

We can correct for it.

But what are the things that we don't yet know about?

And could there be errors in the calibration and in the calibration of the dust loss?

There are lots of potential gotchas.