1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Astrophysics - darkened sun

  1. Dec 14, 2009 #1
    1. The problem statement, all variables and given/known data
    Explain, as quantitatively as you can, what would be observed from Earth if the Sun's surface instantaneously darkened and hence explain why the brightness of a body cannot significantly alter on time scales significantly less than the light travel time across it.

    2. Relevant equations

    Hubble's constant = H
    velocity of galaxy = v
    distance from earth = d
    d = v / H

    redshift = z
    speed of light = c
    z = v / c

    3. The attempt at a solution

    The first thing that came to my mind is that it will take ~ 8 minutes for the photons to reach the Earth, meaning that any observation from the Earth would be 8 min after the event. The Sun is still receding from the Earth. However, we will not be able to calculate the redshift.

    Am I nowhere near what they are looking for in the answer?

    thanks x
  2. jcsd
  3. Dec 14, 2009 #2
    Think about the fact that the Sun is a sphere (almost!), and that the centre of the visible sphere is nearer to you than the edge.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook