--- title: "Curtains of light: the science behind the aurora" description: "The shimmering green and crimson glows of the northern and southern lights are the visible aftermath of a collision between the Sun and Earth's magnetic shield. Here is how, and why, the sky catches fire near the poles." category: "Science" category_url: https://newsparlor.com/category/science author: "Chloe Bennett" published: 2026-06-24T15:43:00.000Z updated: 2026-06-24T15:43:00.000Z canonical: https://newsparlor.com/article/curtains-of-light-the-science-behind-the-aurora tags: ["aurora", "northern lights", "space weather", "solar wind", "magnetosphere", "solar cycle"] --- # Curtains of light: the science behind the aurora The shimmering green and crimson glows of the northern and southern lights are the visible aftermath of a collision between the Sun and Earth's magnetic shield. Here is how, and why, the sky catches fire near the poles. For centuries the aurora was a mystery and a portent, read by different cultures as fire, war or the spirits of the dead. Today the basic physics is well established: the lights are powered by the Sun, sculpted by Earth's magnetic field, and painted by the gases of our own upper atmosphere. ## It starts with the Sun The Sun constantly streams charged particles into space in a flow called the solar wind. When that wind reaches Earth, according to [NASA](https://science.nasa.gov/sun/auroras/), "it can interact with Earth's magnetic shield, often depositing and accumulating energy there. When this energy is finally released, much of it rains down on our atmosphere, causing auroras." The shield is the magnetosphere, the region of space dominated by Earth's magnetic field. The transfer of energy is most efficient when the magnetic field carried by the solar wind points opposite to Earth's. The most dramatic displays follow eruptions on the Sun: solar flares and coronal mass ejections, vast clouds of charged plasma flung from the Sun's surface. When such a cloud strikes Earth, it can trigger a geomagnetic storm that supercharges the aurora. ## Why the lights ring the poles Earth's magnetic field is shaped roughly like a bar magnet, with field lines converging on the magnetic poles. That geometry acts as a funnel. The US National Oceanic and Atmospheric Administration's [Space Weather Prediction Center](https://www.spaceweather.gov/content/aurora-tutorial) (SWPC) explains that accelerated electrons "follow Earth's magnetic field lines towards the north and south magnetic poles where they bombard the upper atmosphere and create the aurora." Because the particles are guided down around the poles rather than straight onto them, the aurora typically forms a ring — the auroral oval — encircling each magnetic pole. That is why the lights are usually seen at high latitudes, across places such as northern Scandinavia, Alaska, Canada and, in the south, around Antarctica. The northern display is the aurora borealis; its southern twin is the aurora australis. ## Where the colors come from The aurora glows because incoming particles transfer energy to atoms and molecules in the thin upper atmosphere, exciting them to higher energy states. As the atoms relax back to normal, they release that energy as light. The color depends on which gas is struck and at what altitude. Oxygen produces the aurora's two most familiar colors. NASA places the common green glow at roughly 100 to 200 kilometers (60 to 120 miles) up, and the deeper red at higher altitudes. Nitrogen contributes blue and, lower down, the pink-to-purple fringes sometimes seen along the bottom of an auroral curtain. The exact altitude bands quoted vary slightly between agencies, but the underlying chemistry — oxygen for green and red, nitrogen for blue and purple — is firmly established. ## When the aurora comes south During strong geomagnetic storms the auroral oval swells outward, pushing the lights toward the equator. NOAA cautions that "during very active times the auroral oval can expand down to latitudes where aurora is rarely seen such as the northern half of the United States and Europe." The great storms of May 2024, among the strongest in two decades, sent auroras as far as Mexico and southern Europe. How often this happens tracks the Sun's roughly 11-year activity cycle. As SWPC puts it, geomagnetic activity and aurora "follow an approximate 11 year cycle." Near solar maximum, when sunspots, flares and coronal mass ejections are most frequent, auroras are more common and reach farther from the poles. The current cycle, Solar Cycle 25, peaked in late 2024, which is why displays have been unusually widespread in recent years. ## Not just an Earthly show The same physics operates wherever a planet has both a magnetic field and an atmosphere. NASA's [Hubble Space Telescope](https://science.nasa.gov/missions/hubble/hubble-captures-vivid-auroras-in-jupiters-atmosphere/) has imaged brilliant ultraviolet auroras over Jupiter, whose magnetosphere is far stronger than Earth's; the Juno spacecraft has studied them from orbit. Saturn has auroras too, though observations combining Hubble with the Cassini mission suggest they are driven largely by the pressure of the solar wind, making them subtly different from Earth's. The aurora, in short, is space weather made visible: a glowing record of the Sun's reach across the solar system, and of the invisible magnetic field that shields the planet beneath it. ## Sources - [Auroras](https://science.nasa.gov/sun/auroras/) - [Aurora Tutorial](https://www.spaceweather.gov/content/aurora-tutorial) - [Hubble Captures Vivid Auroras in Jupiter's Atmosphere](https://science.nasa.gov/missions/hubble/hubble-captures-vivid-auroras-in-jupiters-atmosphere/)