Why is a variable star so convenient for measuring distances to ...

[javeds]

Why is a variable star so convenient for measuring distances to very remote objects?
 
  What will be an ideal response?

Question 2

Which of the following best describes a set of conditions under which archaeoastronomers would conclude that an ancient structure was used for astronomical purposes?
 
  A) The structure has holes in the ceiling that allow viewing the passage of constellations that figure prominently in the culture's folklore, and many other structures built by the same culture have ceiling holes placed in the same way.
  B) They find that, looking out from the center of the building, there are two windows that align with the rise and set points of two bright stars.
  C) The structure has 29 straight lines pointing out from a center, just like there are 29 days in the lunar cycle.
  D) The structure has the same dome shape as modern astronomical observatories.

[tennis14576]

Answer to Question 1

Certain types of variable stars, such as Cepheids and RR Lyrae stars, pulsate with a precise period that is easily determined by observing variations in the star's apparent magnitude. The period of a Cepheid is directly related to the absolute magnitude of the Cepheid and RR Lyrae stars have generally all the same absolute magnitude. When the apparent and absolute magnitudes of a star are known, its distance can be immediately calculated. Because Cepheids, in particular, are among the brightest stars known, they can be seen over large distances. Thus Cepheids are excellent for determining distances to remote objects.

Answer to Question 2

A

[javeds]

Thank you!

[tennis14576]

Always glad to help...