Calculation on Romer's theory of the speed of light

[Gothy]

Homework Statement

As a result of his observations, Romer concluded
that the time interval between eclipses
of Io by Jupiter increased by 20.5 min during
a 5.78 month period as the Earth moved
from a point in its orbit where its motion
is toward Jupiter to a diametrically opposite
point where it moves away from Jupiter. The
presently accepted value of the speed of light
in vacuum is 2.998 × 10⁸ m/s.
Find an average value for the distance between
the Earth and the Sun.
Answer in units of km

c=2.998 × 10⁸ m/s
t= 20.5 min (1230s)
x= ?

Homework Equations

my guess would be the standard velocity equation, v= x/t (x=vt)
but it appears i am wrong, is there another formula that includes velocity and time?

The Attempt at a Solution

v=x/t
x=vt
x= (2.998 × 10⁸ m/s)*(20.5*60)
x= (2.998 × 10⁸ m/s)*1230
x= 3.68751 x 10¹¹ meters
x= 368754000 km

 

[tiny-tim]

Hi Gothy!

Hint: if a lighthouse flashes once a second, what is the difference between the time between the flashes as observed by someone moving towards it at speed v, and by someone else moving away at speed v?