Answer to Question 1
Cepheid variables have a known relationship between their luminosity (absolute magnitude) and their pulsation period. An astronomer can easily observe the pulsation period of the variable star to determine its absolute magnitude and compare this with the apparent magnitude to determine the distance to the star. Cepheid variables are very luminous. This allows them to be seen over very long distances.
Cepheid variables are present in very distant globular clusters, so the distance to these clusters can be determined by studying the Cepheids. The distribution of globular clusters is a key to determining the center of the galaxy, since globular clusters orbit around this center.
Answer to Question 2
Tides are caused by small differences in gravitational forces. For example, Earth's gravity attracts your body downward with a force equal to your weight. The Moon is less massive and more distant, so it attracts your body with a force that is a tiny percent of your weight. You don't notice that little force, but Earth's oceans respond visibly.
Rituals such as the sacrament of the Anointing of the Sick are important expressions of religious be
Peculiar Galaxy NGC 5128 (Centaurus A)
Results of the study by Laruelle et al. (1996)
Eugène Delacroix, Study for The Death of Sardanapalus.
Study of human diseases
The study of how traits such as flower color are passed from generation to generation provided the m