Ancient Lights, in English property law, is the right of a building or house owner to the light received from and through his windows. Windows used for light by an owner for 20 years or more could not be obstructed by the erection of an edifice or by any other act by an adjacent landowner. This rule of law originated in England in 1663, based on the theory that a landowner acquired an easement to the light by virtue of his use of the windows for that purpose for the statutory length of time. Once a right to light exists, the owner of the right is entitled to “sufficient light according to the ordinary notions of mankind”.
Astronomers can measure the distances to other galaxies from their apparent size or brightness. These distances are so great that billions of years are required for their light to reach us. Thus we are actually seeing these galaxies not as they are today, but as they were billions of years ago.
Light travels at c.300,000 km/sec. Even at this speed light takes considerable time to reach us from distant objects. Light from the Sun takes eight minutes to reach us, so that we see the Sun as it was eight minutes ago. Similarly, we see the stars in the nighttime sky as they were decades, centuries and even thousands of years ago.
Galaxies are so distant that their light may take billions of years to reach us. So when we look deeply into space we are looking into the past, across vast gulfs of time. When we study distant galaxies, we find that their stars are still being born from the loose gas from which the galaxies formed. When we study even more distant galaxies, we see them as they were 10 billion or more years ago. In these long-ago galaxies, we find that the stars are just beginning to form.