The farther away you look, the further backward you see

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

29 September 2024

Geofrey Otieno wants to know if it is true that “the farther away an object is, the older it appears”. The straight answer is no. Perhaps Geofrey misunderstood the correct principle, which is that we never see an object as it is right now. We see it the way it was some time ago.

The reason for this is that we can only see something after the light from it lands in our eyes. Since light takes time to travel from the object to our eyes, we can only see how it looked when the light left it.

In normal situations, the time interval is too small to matter. Moving at about 300,000km/second, light takes about 0.00000003 of a second to cover one metre. In fact, the standard metre is defined on the basis of this fact. It is the distance that light travels in the fraction 1/299,792,458 of a second.

With that definition, the speed of light is automatically fixed at exactly 299,792,458 metres per second. There no need to measure it any more since it is fixed by the definition. All electromagnetic radiations (radio-waves and X-rays included)

At about 385,000km away, light take about 1.3 second to travel to the moon. This is not too bad and so, the astronauts who landed on the moon in the late 1960s and early 70s did not have much trouble communicating with earth.

However, if humans do go to Mars, the time delay in communications will be quite a challenge. The distance to Mars varies from about 55 million km to over 350 million km. Thus, the time for radio wave to travel to or from the planet is between 3 minutes (when it is closest) and 20 minutes when it is farthest.

The farthest mand-made object is the Voyager-1 spacecraft which is currently about 25 billion km away. A radio signal takes over 23 hours to get to the craft! We can now appreciate the magnitude of the challenge that scientists faced when they were upgrading the control software on Voyager-1 earlier this year.

They would send some instructions, allow 23 hours for the signal to reach the spacecraft. Then hope that the code was properly interpreted by the on-board computer and wait for confirmation response after another 23 hours.

So, they send the signal today and wait till Tuesday for a response. Science develops high levels of patience in people.