How do we know which stars are close and which stars are far away?
"That's been the single greatest frustration in all of astronomy. Looking at the night sky, even with telescopes, you cannot tell distances. That's been the Holy Grail of astronomy for centuries." -- Michio Kaku, physicist, February 19th 2008
"One of the frightening things I think for conventional astronomers is to accept the fact or to realize that these intrinsic redshifts of the quasars and peculiar galaxies and so forth, active galaxies, means that a lot of the things which we thought were out at great distance in the universe are very much closer in. And in fact you would have to say that what we call the Local Supercluster is much more crowded and contains many more objects than we previously thought." -- Halton C. Arp, astronomer, 2000
Arp, H.C., Cepheid Variables in the Small Magellanic Cloud, Astronomical Journal, Volume 63, Number 2, Page 45, Feb 1958
This difference coupled with the striking difference in amplitude of variation of the shorter period Cepheids opens the question of whether, at a given period, the Cepheids in the galaxy and the SMC have the same luminosity, or mass, or chemical composition.Dear Dr. Arp,
How does one know, by looking at it, if a star is a red giant or a red dwarf?
How do we know the distance to Delta Cephei?
It is said that Delta Cephei is a "yellow-white class F (F5) supergiant" but how do we know it's a supergiant?
Supposing there are frozen sodium ions in between Delta Cephei and the Earth, wouldn't that slow the light down on it's way to the Earth?
Keep up the good work.
Warmest possible regards,