Galaxies identified in the eXtreme Deep Field image can be broken up into nearby, distant, and ultra-distant components, with Hubble only revealing the galaxies it’s capable of seeing in its wavelength ranges and at its optical limits. The changing populations and densities of galaxies reveals a Universe that does, in fact, evolve with time. (Credit: NASA, ESA and Z. Levay, F. Summers (STScI))
We see objects whose light only arrives just now. But we see them as they were in the past: when that now-arriving light was first emitted.
Everything we see is a glimpse into the past.
From atop a high mountain, a distant high mountain several dozens of kilometers, even up to 100 kilometers distant, can be glimpsed on a clear day. At a distance of 100 kilometers, light takes about 33 microseconds to complete a one-way trip. (Credit: Thomas Molck/flickr)
A distant mountaintop 100 kilometers away appears as it did 33 microseconds ago.
Although the Earth might be large and massive compared to the Moon, both bodies are very small compared to the distance between them. It takes about 1.25 seconds for light to travel one-way from the Earth to the Moon, and the Earth-Moon separation is about 30 times the Earth’s diameter. The Earth is also 80 times more massive than the Moon, but its surface gravity is only ~6 times as great. (Credit: James O’Donaghue/NASA imagery)
The Moon’s more distant light arrives from ~1.25 seconds in the past.
Although the light from the Sun might appear to be a “right now” phenomenon, like the silhouettes of the shadows in the foreground, because of its great distance away, its now-arriving light was emitted about 8 minutes and 20 seconds ago. (Credit: helivideo via Adobe Stock)
We see the Sun, 150 million kilometers away, as it was ~8.3 minutes ago.
Pluto is the most distant world visited by a spacecraft created on Earth, and is presently more than 5 billion kilometers distant. From Earth, light from Pluto arrives after a typical journey of just over 5 hours at present. (Credit: NASA/New Horizons/LORRI)
Pluto, at a distance of 5.5 billion kilometers, appears as it did just over 5 hours ago.
