cepheids

> The Polish team also found younger Cepheids lie nearer the centre of the Milky Way, while older Cepheids are further out.

It also assumes that it is impossible for fake Cepheids to exist, which might even confer a reverse association.

Watching that video makes me wonder why so many Cepheids spawned in the sun's wake ~120 million years ago.

How could we know if we're looking at false Cepheids vs real Cepheids, and that there's not multiple types of Cepheids with different causes for pulsations at various brightnesses?

Particularly with Gaia we can now calibrate the luminosities of Cepheids in our galaxy using parallax observations.

TL;DR: two methods (cosmic microwave background, and cepheids) are used to measure the rate of expansion of the universe that give different results.

It figures out that Cepheids are a kind of star, gets a list of the 100 brightest Cepheids, and figures out which are above the horizon at Modesto, CA, right now.

Try these in Google: flights visible from Modesto, CA cepheids visible from Modesto, CA distance from Mars to Jupiter Now try them in WolframAlpha.

A computer simulation revealed there would need to have been star-forming events 64m, 113m and 175m years ago to produce the distribution of Cepheids seen today.

Yes, but Cepheids are calibrated, fundamentally, by parallax.

Having parallax measurements to that distance helps to build multiple versions of the next rung in the ladder (such as Cepheids and the tip of the red giant branch).

What happened is that Hubble relied on Cepheid stars to estimate distances, but he was unaware of the fact that there exist two groups of cepheids, with quite different characteristics.

The debate of "do other galaxies even exist?" wasn't definitively settled until 1923, 99 years ago, with Edwin Hubble's observations of Cepheids in Andromeda.

The comparison to the current Hubble constant (e.g., determined from Cepheids) is made by evolving the CMB Hubble "constant" value to today, under the assumption of our best cosmological model model.

"researchers started using Cepheids to calibrate the distances to bright supernovas, enabling more accurate measurements of H0." It seems like if there were some error in the luminosity measurement for cepheids, it would propagate to the measurements with supernovas...

("appears" since we can't directly measure actual distances, but observe that galaxies get smaller/fainter/redder together) Cepheids are a relatively common kind of star that pulsates regularly during its lifetime, while SuperNovas are much rarer one-time very bright events.

This meant that measurements of distances to neighboring galaxies were wrong, since they included a mixture of classical and Type II Cepheids.

One thing I've always admired as a Layman about astronomy, is all the eloquent deductions they've been able to make that adds another framework of ways to discover new information, particularly the discovery of Cepheids.

For measurements of dark energy this very quickly gets you into the weeds of Type Ia supernova physics (which is made more difficult because we don't know for certain what Type Ia supernovae are), stellar physics in Cepheids, the effect of metallicity, selection bias effects, and on and on.