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
Gravitational waves are ripples in the fabric of space-time, produced when massive objects accelerate. Einstein predicted them in 1916 but thought they would be too weak to detect. A century later, he was proven right on the first point and wrong on the second. The first detection On September 14, 2015, the two LIGO detectors … 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
Astronomy is probably the oldest science. People watched the sky to keep time, plan harvests, navigate and make sense of their place in the world long before writing existed. Ancient skywatchers Greek models Greek thinkers sought geometric explanations. Eratosthenes estimated Earth’s circumference around 240 BCE. Aristarchus proposed that Earth orbits the Sun, but the Earth-centered … 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
Since Sputnik in 1957, space exploration has achieved astonishing things: humans on the Moon, rovers on Mars, probes beyond the heliosphere. But every mission still faces hard problems, and sending people farther than the Moon multiplies them. Radiation Beyond Earth’s protective magnetic field, astronauts are exposed to galactic cosmic rays and solar particle events, which … Read more
An exoplanet is a planet orbiting a star other than the Sun. The first ones were confirmed in the 1990s, and the NASA Exoplanet Archive now lists more than 6,000. Most are never seen directly: they are detected through their effects on their star. The transit method When a planet passes in front of its … Read more
A supernova is the explosion of a star, briefly bright enough to outshine an entire galaxy. These explosions forge and scatter many of the elements in our bodies and planets, and leave behind neutron stars and black holes. Two main kinds Core-collapse supernovae (Types II, Ib and Ic) happen when a massive star, more than … Read more
Every star is born in a cloud of gas and dust and spends its life in a balance between gravity, which pulls inward, and the pressure of nuclear fusion pushing outward. Its mass at birth decides how long it lives and how it dies. Birth in molecular clouds Stars form in cold, dense clouds of … Read more
