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Cosmos · Sciencepedia

Cosmos

36 articles

From the Sun next door to galaxies billions of light-years away — space, astronomy, and humanity's journey beyond Earth.

Subtopics

The Solar System18 Stars and Galaxies6 Space Exploration3 Cosmology4 Observing the Sky5 History of Astronomy0

The Big Bang: 13.8 billion years, step by step

Not an explosion in space but the expansion of space itself. The timeline from 10⁻⁴³ seconds to today, the three pillars of evidence, and why the universe's fate was rewritten in 1998.

The multiverse: four levels and one hard question

First, two things often confused: the observable universe has a boundary; the universe may not. Then Max Tegmark's four levels of multiverse — and whether any of it counts as science.

Stars and Galaxies

White holes and wormholes: two solutions nobody has seen

They come out of the same equations as black holes, yet black holes have been photographed while these two have never been observed. Why they almost certainly do not exist in the visible universe.

The Solar System

The eight planets of the Solar System

The Solar System has eight planets — a number settled only in 2006, when the IAU set three criteria and Pluto failed the third.

The Solar System

Why planets spin on their axes

Nothing set the planets spinning by hand. Their rotation is the sum of billions of off-centre impacts in the protoplanetary disk — and sometimes one collision was enough to flip everything over.

The Solar System

The Sun: the reactor that holds a system together

The Sun holds 99.86% of the Solar System's mass and fuses 600 million tonnes of hydrogen every second. All light, weather and life on Earth trace back to it.

The Solar System

Kepler's three laws: the rules planets move by

Orbits are ellipses, not circles; planets move faster when near and slower when far; and one formula ties period to distance for everything orbiting the Sun.

Stars and Galaxies

Galaxies: what they are and how they are classified

The band of light across the night sky is our own galaxy's disk, seen from inside it. Beyond it lie hundreds of billions more, and their shapes record their collision histories.

Stars and Galaxies

Stars: structure and life cycle

A ball of gas becomes a star only when heavy enough to ignite fusion — about 80 Jupiter masses. Initial mass then decides nearly everything else, including how it dies.

The Solar System

Why Pluto is no longer a planet

Pluto lost nothing — the definition changed. It began with the 2005 discovery of Eris, more massive than Pluto, forcing astronomers to choose between many more planets or one fewer.

Stars and Galaxies

The 20 brightest stars in the night sky

Ranked by apparent magnitude — brightness as seen from Earth, not true luminosity. Sirius leads because it is close; Deneb makes the list from hundreds of times farther away.

The Solar System

Jupiter: the fastest-spinning planet and its invisible brake

Eleven times wider than Earth, yet it turns once every 9 hours 55 minutes. Why Jupiter spins so fast — and what slowed it down.