fjernhode, i think that the distance that we measure today is just to put things in a rough map. Many of the methods that they are using will be superceeded by much more accurate methods in time.

I think it is interesting about these stars that "dim" from time to time. I wonder is this a sign that they may have planets that are orbiting them.

---

I think it is interesting about these stars that "dim" from time to time. I wonder is this a sign that they may have planets that are orbiting them.

The brightening and dimming of Cepheids happens because they expand and contract in a regular cycle, not because of planets passing in front of them. Cepheids are large stars and much more luminous than the sun. The dimming effect of a planet passing in front of a star is a great deal less than the change in brightness of Cepheids. Too bad, it would make finding planets a lot easier if it were true because there are a lot of known Cepheids.

---

I forgot to mention that astronomers today do know the distances very well
because there are the two things having the names of "red shift" and
Supernovae (or -novas) Type Ia. At least the latter is quite definitive
because they are all equally bright all the way or at max.

I've read a new class of supernovae has beeen discovered and this may change the role of "standard candles" of supernovae Type Ia.
Tullio

---

I have to post this question.

In the first half of the twentieth century, Dr. Walter Baade used the 2.5 m as well as the 5 m telescopes and was able to estimate the distance to the Andromeda Galaxy as 750.000 light years. He used cepheids as a reference. There are two types of Cepheids, Type I and Type II. Delta Cephei is the classic example of a Type I Cepheid. There are also dwarf cepheids as well as other variables with regular periods and amplitudes. The Pole Star is said to be a Type II Cepheid, but it only varies with a tenth of a magnitude with a period of 4 days. Its spectral class makes me assume that the Pole Star is a class I Cepheid. Newer literature describes the Pole Star as having stopped pulsating and is having the same brightness all the time.

An example of a class II cepheid is W Wirginis. My guess is that class II cepheids would not be detectable in the Andromeda Galaxy by the 2.5 m and 5 m telescopes. Today the Andromeda Galaxy is estimated to be 2.25 million light years away. A somewhat lesser distance may earlier have been assumed as well.

So the distance has tripled but the base material is the same. What conclusion has been made to get to the current distance estimate for the Andromeda Galaxy ?

Regards,
fjernhode

Everybody knows that millions of eons ago, Vega was the equivalent to Polar Bear. I don´t knowif that anserw your questuions...

---

About 13,000 years ago Vega was the North Pole Star, because of precession.

---

It could be that both people were right in the estimate, and that the galaxies are moving apart....