What the numbers mean
Daylight carries an eight-minute delay.
Light crosses one astronomical unit in about 499 seconds. What reaches Earth now left the Sun roughly eight minutes earlier. Even our nearest star is something we see in the past.
Read the sourcesA very fast traveller, a very long trip
Light travels through a vacuum at exactly 299,792,458 metres per second in the international system of units. Across a room, the delay is far too short for us to notice. Across the roughly 150 million kilometres between the Sun and Earth, even light needs several minutes to arrive. [2]
One unit makes the Solar System smaller
Astronomers use the astronomical unit, or AU, to express distances within the Solar System. NASA's Jet Propulsion Laboratory gives its exact definition as 149,597,870,700 metres. Dividing this length by light's speed gives about 499 seconds. Earth's orbit is not a perfect circle, so the real Sun–Earth travel time varies through the year. [1]
Looking farther means looking earlier
NASA explains that we see objects as they were when their light began its journey. The delay grows with distance: minutes within parts of the Solar System, years for nearby stars and much longer for distant galaxies. One telescope image can contain light that set out at very different times. [3]