The Sun's increasing luminosity will evaporate Earth's oceans, ending habitability.

Earth's Oceans Boil

The Sun's luminosity increases by roughly 1% every 110 million years. Within approximately 1 billion years, it will be 10% brighter than today, triggering a "moist greenhouse" effect. Earth's oceans will begin evaporating into the atmosphere, where UV radiation will split water molecules. Hydrogen will escape to space. The planet will become permanently uninhabitable — long before the Sun becomes a red giant.

Sun brightening ends Earth habitability

The Sun exhausts its hydrogen fuel, expands into a red giant, and likely engulfs Earth.

Sun Becomes a Red Giant

In approximately 5 billion years, the Sun will exhaust the hydrogen in its core and enter the subgiant phase. Over the following 1–2 billion years, it will expand into a red giant, reaching a maximum radius of about 1.2 AU (beyond Earth's current orbit) at around 7.6 billion years. By this point, the Sun will have lost roughly a third of its mass, and Earth's orbit will have expanded outward — but likely not enough to escape engulfment. Mercury and Venus will be consumed first. The Sun will eventually collapse into a white dwarf.

Sun leaves the main sequence; red giant era follows

Betelgeuse will explode as a Type II supernova, visible from Earth in daylight.

Betelgeuse Supernova

Betelgeuse (Alpha Orionis) is a red supergiant approximately 640 light-years away, nearing the end of its life. It is roughly 1,000 times the Sun's radius and 16–20 solar masses. When it explodes, it will briefly shine as bright as the half-Moon, visible during the day for weeks to months. A 2023 study suggested Betelgeuse may be in late-stage core carbon burning, potentially placing the supernova "tens of years" away — though the 2025 discovery of its binary companion "Siwarha" introduced new uncertainty, pushing estimates back toward the 100,000-year range. At 640 light-years, Earth is well beyond the ~160 light-year danger radius for supernova radiation effects.

A likely naked-eye supernova on human timescales

The Milky Way and Andromeda may collide/merge; probability revised with newer dynamics.

Milky Way–Andromeda Merger

Andromeda (M31) is approaching the Milky Way at approximately 110 km/s, separated by about 2.5 million light-years. For over a century, astronomers predicted an inevitable collision. However, a landmark 2025 study by Sawala et al., published in Nature Astronomy, factored in the gravitational effects of the Large Magellanic Cloud and Triangulum Galaxy (M33) — finding only a roughly 50% chance of collision within 10 billion years. If it happens, the two spirals will merge over billions of years into a single elliptical galaxy dubbed "Milkomeda." Stars themselves are unlikely to collide, but the two central supermassive black holes — Sagittarius A* and Andromeda's nucleus — would eventually merge.

A possible galactic merger (not guaranteed)

Star formation ends and the longest-lived red dwarfs burn out, ending the stelliferous era.

Last Stars Die

Star formation will cease in 1–100 trillion years as interstellar gas is exhausted. The longest-lived stars — tiny red dwarfs with about 0.08 solar masses — will take up to 10 trillion years to exhaust their hydrogen fuel. After the last red dwarf fades, the universe enters the "Degenerate Era": a dark cosmos populated only by stellar remnants (white dwarfs, neutron stars, black holes) slowly cooling toward absolute zero.

End of the stelliferous era (scale beyond numeric clock)

The universe reaches maximum entropy; no further work, structure, or life is possible.

Heat Death of the Universe

The prevailing theory for the ultimate fate of the universe. As expansion continues, all energy gradients dissipate. Black holes — the last complex structures — evaporate via Hawking radiation over timescales of 10^100 years for supermassive black holes. If protons decay (predicted by some Grand Unified Theories but never observed, with an estimated half-life of ~10^34 years), all remaining matter disintegrates into subatomic particles and radiation. The universe becomes a cold, diffuse gas of photons and leptons at a temperature approaching absolute zero. No thermodynamic processes can occur. Time itself becomes effectively meaningless.

Heat death (maximum entropy; scale beyond representation)

Time until humanity's farthest spacecraft makes its closest stellar encounter.

Voyager 1 · Gliese 445

Voyager 1, launched in 1977, is the most distant human-made object. Its trajectory will carry it within 1.6 light-years of Gliese 445, a red dwarf in Camelopardalis, in approximately 40,000 years.

Voyager 1 approaches Gliese 445

Countdown to the closest flyby of a large asteroid in recorded history.

Apophis Close Approach

On April 13, 2029, asteroid 99942 Apophis — 370 metres wide — will pass within 31,000 km of Earth. Closer than geostationary satellites. Visible to the naked eye. NASA has confirmed zero impact risk.

Apophis passes closer than satellites

Time until the next full eruption of the Yellowstone caldera.

Yellowstone Supervolcano

Beneath Yellowstone lies one of Earth's largest active volcanic systems. Three cataclysmic eruptions in 2.1 million years — the last 631,000 years ago. A full eruption would bury North America in ash and trigger a volcanic winter.

Yellowstone caldera eruption

Time until Earth's magnetic poles flip — weakening our shield against solar radiation.

Magnetic Field Reversal

Earth's magnetic field has reversed hundreds of times. The last full reversal was 780,000 years ago. On average they happen every 200,000-300,000 years — we are statistically overdue.

Earth's magnetic poles reverse

Time remaining before cumulative CO2 emissions exhaust the carbon budget for 1.5C warming.

Climate Habitability Window

This clock counts down to the moment the global carbon budget for limiting warming to 1.5C is fully exhausted at current emission rates. The IPCC Sixth Assessment Report estimated that from the start of 2020, humanity had roughly 400 billion tonnes of CO2 it could still emit for a 67% chance of staying below 1.5C. Global emissions have continued at over 40 GtCO2 per year. This clock shows how much time remains at the current rate of depletion.