How big is Great Nebula in Carina? | Scale of the Universe

The Great Nebula in Carina, usually called the Carina Nebula, is a vast cloud of glowing gas and dust in the southern constellation Carina. It is about 7,500 light-years from Earth, where a light-year is the distance light travels in one year. New stars are forming in it, alongside some of the most massive stars known. Its glowing gas spans about 390 to 650 light-years, depending on how faint a glow is counted.

Size

The nebula fades gradually at its edges, so published sizes differ widely. ESO, the European Southern Observatory, describes it as spanning about 100 light-years, and NASA gives about 300 light-years. Measurements that include the faint outer gas give larger figures.

Deep images show filaments and bubbles of glowing gas spanning more than 3 degrees of sky. That is more than 120 parsecs, where a parsec is about 3.26 light-years, or more than 390 light-years. A comparison of giant glowing gas clouds in the Milky Way and nearby galaxies lists the nebula as about 200 parsecs, or 650 light-years, across. That figure is marked as uncertain.

The size shown above, 4.4 exameters, is 4.4 × 10¹⁸ meters, where 10¹⁸ is a 1 followed by 18 zeros. That is about 465 light-years, within the measured range. The nebula's distance is known to within about 2%. Astronomers worked it out mainly from the Homunculus Nebula, a cloud of gas expanding from the star Eta Carinae near the nebula's heart, by comparing how fast the cloud grows on the sky with how fast its gas moves.

Size comparisons

Seen from Earth, the nebula's faint outer gas spans more than five times the width of the full Moon.
Omega Centauri, the most massive globular star cluster known in the Milky Way as of 2026, has a bright main body 150 to 190 light-years across, less than half the width of the Carina Nebula's glowing gas.
"Mystic Mountain", a pillar of gas and dust inside the nebula, is 3 light-years tall. If it were shrunk to the height of a person 1.7 meters (5 feet 7 inches) tall, the whole nebula would be about 220 to 370 meters (730 to 1,210 feet) wide.
The nebula is about 90 to 150 times as wide as the distance from the Sun to Proxima Centauri, the nearest star.

Eta Carinae

Eta Carinae is a system of at least two stars. The larger one has about 100 times the mass of the Sun and gives off about 5 million times as much light. In the 1840s it flared up and was the second-brightest star in the night sky for several years, and it had faded from view by the 1870s. During that outburst it threw off more than 10 times the Sun's mass of gas, which formed the Homunculus Nebula.

Stars as massive as this live only about 3 million years before exploding as supernovae, the explosions of massive stars. Eta Carinae is likely to explode in the near future, by astronomical standards. Several supernovae are expected in the Carina Nebula within the next 1 to 2 million years.

A nursery for massive stars

The nebula glows because of ultraviolet light from its hottest, most massive stars. Today it is lit mainly by 65 very hot stars of the kind called O-type. For most of the nebula's life, its stars gave off about 150 times as much of the ultraviolet light that makes hydrogen glow as the stars of the Orion Nebula do.

This radiation, along with winds from the stars, is squeezing the surrounding clouds of cold gas. That triggers new stars to form around the edges of the nebula, while the same radiation evaporates the clouds they form from. Nicolas-Louis de Lacaille discovered the nebula in 1752 from the Cape of Good Hope.