TON 618 sits 10.4 billion light-years away and still registers in modest telescopes. Bring it closer and the calculus inverts: at some point the view is sublime, then it cooks the planet, then it eats us. Move the dial.
A glowing disk pinned to the night sky, brighter than the moon, faintly resolved as a structure rather than a point. The accretion ring is visible. Two pencil-thin jets extend perpendicular for arc-minutes. Earth is fine. The Oort cloud is being slowly stripped, but on geological timescales.
A logarithmic scale where every 5 magnitudes is a factor of 100 in brightness, and lower numbers are brighter. The Sun is −26.7, the full moon −12.7, the faintest naked-eye star +6. Starting from TON 618's measured magnitude at its real distance, we just rescale by inverse-square dimming.
The disk's physical diameter divided by its distance gives an angle in radians. The constant 206,265 just converts radians to arcseconds, the unit astronomers use for tiny angles. The full moon spans about 1,800″ (half a degree). Naked-eye resolution maxes out around 60″.
The Pogson relation, which inverts the magnitude scale into a flux ratio. A 5-magnitude difference is exactly 100×. Negative ratios don't exist; the formula is built so that brighter wins, regardless of which side has the lower number.
The radius around the Sun where its gravity still wins against TON 618's. Beyond this, an object is no longer bound to us. The cube-root scaling makes this the most forgiving of the gravitational effects, but it shrinks fast as TON 618 gets closer. Today's value (against the galactic potential) is roughly 4 ly.
TON 618 is a quasar, an active galactic nucleus powered by one of the most massive black holes ever measured at roughly 40 billion solar masses. The "TON" comes from the Tonantzintla catalogue, compiled at a Mexican observatory in the late 1950s, where it was first noted as a faint blue object. Decades later, spectroscopy revealed the absurdity of the thing. Its accretion disk outshines the entire Milky Way by a factor of about 140 trillion to one.
Roughly 10.4 billion light-years away, with a redshift of z = 2.219. The photons reaching telescopes today left TON 618 when the universe was less than a third of its current age. Because space has been expanding the whole time, its present location has drifted to about 18 billion light-years from us. It is one of the most distant individual objects easily picked up by amateur astronomy.
The premise of this page was a tweet that pointed out: if TON 618 sat where Alpha Centauri does (4.37 ly), the night sky would be unrecognizable. That is correct, and a wild understatement. The conversation that followed worked through gravity, then radiation, then the math. This page is the visual version. Move the slider. Watch the universe break.