How big is Lagoon Nebula? | Scale of the Universe

The Lagoon Nebula is a giant cloud of gas and dust where new stars are forming, about 4,300 light-years from Earth in the constellation Sagittarius. A light-year is the distance light travels in one year, about 9.46 trillion kilometers. The nebula is about 100 light-years, or 950 trillion kilometers, across. Its name comes from a wide, dark lane shaped like a lagoon that divides its glowing gas into two parts.

Size

The Lagoon Nebula is an H II region, a cloud of hydrogen that glows because ultraviolet light from massive young stars has stripped electrons from its atoms. The European Southern Observatory (ESO) describes it as a giant cloud 100 light-years across. A 1959 catalog of these glowing clouds lists its width on the sky as 90 arcminutes, or 1.5 degrees, where an arcminute is 1/60 of a degree.

In 2019, astronomers measured the distance to about 900 of the nebula's young stars with the Gaia space telescope. They found about 4,300 light-years, and at that distance 90 arcminutes is about 110 light-years. Pages from NASA and ESO give figures between about 4,000 and 5,200 light-years.

Like other glowing clouds, the nebula fades out gradually, so its size depends on how much of the faint glow is counted. A 2017 study that mapped gas across the face of the nebula used an image about 66 by 41 light-years across. The nebula itself is the lit-up part of a much larger, darker cloud of gas that stretches about 160 light-years.

Size comparisons

The Lagoon Nebula is about four times as wide as the Orion Nebula, which spans about 24 light-years.
It is about 24 times the distance from the Sun to Proxima Centauri, the nearest star.
The disk of the Milky Way, about 100,000 light-years across, is about 1,000 times as wide as the Lagoon Nebula.
On the sky, the nebula is almost three times as wide as the full Moon.
If the Lagoon Nebula were shrunk to the length of a marathon, 42.195 kilometers (26.2 miles), the orbit of Neptune would be about 40 centimeters (16 inches) across. Proxima Centauri would be about 1.8 kilometers (1.1 miles) from the Sun.

Where stars are forming

The young star cluster NGC 6530 lies near the middle of the nebula, slightly in front of it. Its stars are only 1–2 million years old. Most of the ultraviolet light that makes the gas glow comes from two massive stars, 9 Sagittarii and HD 165052.

Dark patches scattered across the nebula are dense clouds of gas and dust collapsing under their own weight, and they will form new clusters of stars. The smallest of these clouds are called globules. Near the center, a small region called the Hourglass holds two twisting, tornado-like funnels of gas, each about half a light-year long.

Seeing the Lagoon

The Italian astronomer Giovanni Battista Hodierna discovered the Lagoon Nebula in 1654. It is also known as Messier 8, from the catalog of Charles Messier. It is faintly visible to the unaided eye under dark skies and shows clearly in binoculars or a small telescope. NASA gives August as the best month to observe it.