Galaxies did not exist at the very beginning. The early universe was a nearly smooth hot gas. Tiny differences in density, visible today in the cosmic microwave background, grew over hundreds of millions of years into the galaxies we see. Dark matter first According to the standard model of cosmology, dark matter clumped first, because … Read more
The Milky Way is our home galaxy: a barred spiral of hundreds of billions of stars, including the Sun. It is an ordinary galaxy among hundreds of billions in the observable universe, but it is the only one we can study from the inside. Size and structure Where are we? The Sun sits about 26,000 … Read more
A quasar is the extremely bright core of a distant galaxy, powered by a supermassive black hole swallowing gas. A single quasar can outshine all the stars of its host galaxy combined, which makes quasars visible across billions of light-years. How quasars were found In the 1950s, radio astronomers found sources that looked like stars … Read more
The universe is about 13.8 billion years old. That figure comes mainly from measurements of the cosmic microwave background, and it is supported by independent checks on the oldest objects we can see. Method 1: the cosmic microwave background The cosmic microwave background is light released about 380,000 years after the Big Bang. The size … Read more
The James Webb Space Telescope (JWST) is the largest and most powerful space telescope ever built. A partnership between NASA, the European Space Agency and the Canadian Space Agency, it launched on December 25, 2021 (NASA’s Webb mission page) and began science operations in July 2022. Key features Why infrared? Main discoveries so far Webb … Read more
According to Einstein’s general relativity, mass curves space, so light passing near a massive object follows a bent path. A galaxy or cluster can act like a giant, imperfect lens that magnifies and distorts the light of objects behind it. A famous confirmation During the total solar eclipse of 1919, expeditions led by Arthur Eddington … Read more
Spectroscopy means spreading light into its colors, a spectrum, and studying it in detail. It is one of the most powerful tools in astronomy: from a point of light, it can reveal what a star is made of, how hot it is, how fast it moves and much more. Spectral lines: chemical fingerprints Every element … Read more
Almost everything we know about the universe comes from light. A telescope’s main job is not to magnify but to collect as much light as possible and focus it into an image. Refractors and reflectors An eyepiece or a camera then magnifies or records the focused image. Aperture is what counts Seeing through the atmosphere … Read more
How the universe will end depends mainly on dark energy, the mysterious component that is making the expansion of space speed up. Nobody knows for sure, but current observations point toward a long, cold fade. The discovery that changed everything In 1998, two teams studying distant Type Ia supernovae found that they were dimmer than … Read more
Dark matter is matter that does not emit, absorb or reflect light, yet its gravity shapes galaxies and the whole universe. Ordinary matter, everything made of atoms, is only about 5 percent of the universe’s total content. Dark matter accounts for roughly 27 percent, and dark energy the remaining 68 percent or so. The evidence … Read more
