I need Help (Guidance)

1. What objects Hershel and Shapley, respectively, used to map the Galaxy? What were their results and why did they come up with such different dimensions of our Galaxy? 2. What are the four major parts of our galaxy? Summarize their main properties? What...

The calcium II K line has a rest wavelength of l0 = 393.36 nm. You observed this line in the spectrum of a galaxy, and found that the observed wavelength of this line is l = 421.76 nm. What is the distance to this galaxy? You may use Hubble constant H0 =...

OPTICS: URGENT QUESTION-- DETAILS PLEASE What's the paraxial approximation, in spherical mirrors? start from the equation \left(x-R\right)^2+y^2=R^2(x−R) 2 +y 2 =R 2 , which represents a circle of radius RR with the center at x=R, and solve for x. Now use...

Thank you!