Cosmic timeline

At a glance

Key points

Compressed into one calendar year, the Sun forms around 31 August and all of recorded history fits in the last 14 seconds of 31 December.

• 13.787 billion years old
• Webb sees back to 280 million years
• Recorded history: the last 14 seconds of the cosmic year

Dark ages to first light

After the CMB was released, the universe went dark until the first stars ignited, roughly 100–200 million years later. Webb now sees galaxies from less than 300 million years after the Big Bang.

A cosmic calendar

Scale 13.8 billion years to one year and each day is about 38 million years. The Sun forms at the end of August, and the dinosaurs vanish on 30 December.

The first minutes

In the first second the universe was a hot, dense soup of particles and radiation, cooling as it expanded. Between about 3 and 20 minutes, protons and neutrons fused into helium nuclei, leaving roughly three-quarters hydrogen and one-quarter helium by mass, with traces of deuterium and lithium. Every heavier element, from the carbon in your cells to the iron in your blood, was made much later inside stars and in stellar explosions and collisions.

Clearing the fog

Ultraviolet light from the first stars and galaxies gradually split apart the neutral hydrogen that filled space, a process called reionisation. Planck's measurements of the CMB indicate it was well under way several hundred million years after the Big Bang, and quasar spectra show it was largely finished within about a billion years. Webb is now seeing the galaxies that may have done the work.

Reading the timeline

Each era is known in a different way: the first minutes from the abundances of light elements, the release of the CMB from the microwave sky, the first galaxies from deep Webb images, and the ages of the Sun and Earth from radioactive dating of meteorites. Before about one second after the Big Bang, the story rests mainly on theory and indirect clues rather than direct observation.

Missions

1. 2009–2013

   Planck

   ESACompleted

   Mapped the cosmic microwave background at the highest precision to date.

2. 2021–

   James Webb Space Telescope

   NASA / ESA / CSAActive

   Infrared observatory at Sun–Earth L2, about 1.5 million km from Earth.

   Mission page (opens in a new tab)

Related entries

• Cosmic microwave backgroundThe oldest light in the universe
• MoM-z14 and JADES-GS-z14-0The most distant galaxies confirmed
• Dark matter and dark energyThe 95% we cannot see

Sources

1. Particle Data Group: Big-Bang nucleosynthesis review (2024) (opens in a new tab)
2. Planck Collaboration 2018, A&A 641:A6 (arXiv) (opens in a new tab)
3. ESA: Planck and the cosmic microwave background (opens in a new tab)
4. NASA Science: Webb pushes boundaries of the observable universe (opens in a new tab)
5. NASA Science: Sun facts (opens in a new tab)

Last reviewed 10 Oct 2026 against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.