How big is Ring Nebula? | Scale of the Universe

The Ring Nebula is a glowing shell of gas thrown off by a dying star, about 2,600 light-years from Earth in the constellation Lyra. A light-year is the distance light travels in one year, about 9.46 trillion kilometers. The nebula's bright ring is about 1 light-year, or roughly 10 trillion kilometers, across. A much fainter halo of gas around it reaches about 3 light-years across.

Size

The Ring Nebula is a planetary nebula: the outer layers of a star, cast off near the end of its life. Like any cloud of gas, it has no hard edge, so its size depends on which part is measured.

The bright ring is slightly oval. On images from the James Webb Space Telescope, its outer edge measures about 88 by 70 arcseconds on the sky, where an arcsecond is 1/3,600 of a degree. At the nebula's distance, that is about 1.1 by 0.9 light-years. NASA describes the nebula as roughly 1 light-year across.

Turning an angle into a length needs the distance. The best measurement comes from the Gaia space telescope. It measured the central star's parallax: the tiny shift in the star's position as Earth travels around the Sun. That puts the nebula about 2,600 light-years away, give or take about 100 light-years.

Beyond the bright ring lies a faint halo. Including it, the nebula is about 4 arcminutes (240 arcseconds) wide, or about 3 light-years at that distance.

Size comparisons

The bright ring is about one-third of a parsec across, and the nebula with its halo about one parsec. A parsec is a unit of distance equal to about 3.26 light-years.
The ring's longest width is about a quarter of the distance from the Sun to Proxima Centauri, 4.2 light-years.
The Boomerang Nebula, a cloud of gas thrown off by another dying star, is about 2 light-years long, roughly twice the width of the Ring Nebula's bright ring.
The ring contains about 20,000 dense clumps of gas. A typical clump is about 150 astronomical units across, where 1 astronomical unit is the average distance from Earth to the Sun. That is about two and a half times the width of the orbit of Neptune.
If one of those clumps were shrunk to the size of a basketball, the bright ring would be about 110 meters (360 feet) long, and Neptune's whole orbit would be a circle about 10 centimeters (4 inches) across.

How the ring formed

The central star threw off this gas about 4,000 years ago. The star began with several times the mass of the Sun. Over its long life it turned hydrogen into helium, and when it ran low on fuel, it swelled into a red giant and shed its outer layers. What remains is becoming a white dwarf, a small, dense and very hot star.

Ultraviolet light from the star makes the surrounding gas glow. The nebula is expanding at more than 69,000 kilometers per hour (43,000 miles per hour). It will keep expanding for about another 10,000 years, fading until it merges with the thin gas between the stars. The Sun, which has less mass, is expected to shed its own outer layers in about 6 billion years, making a fainter, more spread-out nebula.

The shape of the ring

The Ring Nebula is not a flat ring. It is shaped like a distorted doughnut, and Earth looks almost straight down one of its poles. The center is not empty: gas of lower density fills it, stretching toward and away from Earth in a shape like a rugby ball.

Webb's images also show about ten faint, evenly spaced arcs a little beyond the edge of the ring. Astronomers think a smaller companion star, circling the central star about once every 280 years, shaped them. The nebula was discovered in 1779 by Antoine Darquier de Pellepoix and Charles Messier, who came across it while following a comet. It is also known as M57 and NGC 6720.