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Although light travels at a constant speed of around 300000km/sec in a vacuum, its actual travel distance is further as the space it travels through is expanding.
Here's a simple analogy.
I leave a jetty and head down stream in a boat which has an average speed of 20kph in still water. After 2 hours, I have travelled 40km. Right!
Wrong! The river is flowing at 10kph, so the total distance travelled in 2 hours is actually 60km.
Of course, space is not actually flowing but it is stretching or expanding, but the effect is somewhat similar.
Regards, Rob
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