RationalWiki's 2020 Fundraiser

There is no RationalWiki without you. We are a small non-profit with no staff – we are hundreds of volunteers who document pseudoscience and crankery around the world every day. We will never allow ads because we must remain independent. We cannot rely on big donors with corresponding big agendas. We are not the largest website around, but we believe we play an important role in defending truth and objectivity.

If everyone who saw this today donated $5, we would meet our goal for 2021.

Fighting pseudoscience isn't free.
We are 100% user-supported! Help and donate $5, $20 or whatever you can today with PayPal Logo.png!

Donations so far: $1680Goal: $3500

Cepheid Variable

From RationalWiki
Jump to: navigation, search

Cepheids are a class of stars whose absolute magnitude (luminosity) tallies extremely closely with their period of varibility. Knowing this period, astronomers can compare the star's absolute magnitude with its observed magnitude, and determine quite accurately its distance from Earth [1].

The relationship between periodicity and luminosity was discovered and then experimentally verified using the parallax method for close-by Cepheids.

Cepheid variables were observed in the Andromeda Galaxy by Edwin Hubble in the early 1920s, proving conclusively that Andromeda is far too distant to be part of our Milky Way [2]. This was the first indication that the universe extends beyond our own galaxy. Later observations of the red shift of more distant galaxies showed that the universe is expanding, providing the first empirical evidence for the Big Bang theory.