## College Physics (4th Edition)

Let $\Delta t_0$ be the interval in the spaceship frame. Let $\Delta t$ be the interval in the Earth frame. We can find the interval measured in the Earth frame: $\Delta t = \frac{\Delta t_0}{\sqrt{1-\frac{v^2}{c^2}}}$ $\Delta t = \frac{12~h}{\sqrt{1-\frac{(0.87~c)^2}{c^2}}}$ $\Delta t = \frac{12~h}{\sqrt{0.2431}}$ $\Delta t = 24~h$ The reports are sent to Earth every 24 hours according to Earth clocks.