The Rosette Nebula is a large, round cloud of glowing gas with a hollow center, in the constellation Monoceros. It is about 4,600 to 4,900 light-years from Earth. A light-year is the distance light travels in one year, about 9.46 trillion kilometers. The nebula is about 130 to 170 light-years across, depending on where its faint outer edge is drawn.

Size

The Rosette is a thick shell of glowing gas around a central hollow, and its outer edge fades gradually. A 1959 catalog of glowing hydrogen clouds gives its greatest width as 100 arcminutes, where an arcminute is one-sixtieth of a degree. A 2025 study that mapped the nebula's light found it filling a field about 2 degrees across.

Turning an angle on the sky into a width needs the distance. Recent measurements, including ones from the Gaia space telescope, put the nebula about 4,600 to 4,900 light-years away. At that distance, 100 arcminutes is about 130 to 140 light-years, and the 2025 study gives about 160 to 170 light-years.

The size shown above, 1.2 exameters, is 1.2 × 10¹⁸ meters, where 10¹⁸ is a 1 followed by 18 zeros. That is about 127 light-years, close to the small end of the measured range.

Size comparisons

Seen from Earth, the nebula is about three to four times as wide as the full Moon.
Omega Centauri, the most massive globular star cluster known in the Milky Way as of 2026, is about the same width: its bright main body is about 150 to 190 light-years across.
The nebula is about 30 to 40 times as wide as the distance from the Sun to Proxima Centauri, the nearest star.
If the orbit of Neptune around the Sun were shrunk to the width of a U.S. penny, 19 millimeters (0.75 inches), the nebula would be about 2.6 to 3.4 kilometers (1.6 to 2.1 miles) across.

What cleared the center

At the center of the nebula is a young star cluster, NGC 2244, about 2 million years old. Its brightest stars are massive and very hot. Their light knocks electrons off the atoms in the surrounding gas, which makes the gas glow.

The same stars blow out powerful winds. Measurements of the gas in the hollow show it streaming outward at up to 20 kilometers per second (72,000 kilometers per hour), a sign that the winds are clearing the center. The glowing gas that remains has about 23,000 times the mass of the Sun.

The expanding nebula is running into a much larger cloud of cold gas, the Rosette Molecular Cloud. Several clusters of new stars have recently formed inside that cloud.

Many names for one nebula

The Rosette has several catalog numbers. NGC 2237 first referred to the brightest patch on its western side, and NGC 2246 to a bright area on its eastern side. The central cluster is NGC 2244, but it has also been listed as NGC 2239, a name first given to its brightest star.

The astronomer Flamsteed noticed the cluster in the late 1600s. William Herschel later reported the cluster without noticing the glowing gas around it. His son, John Herschel, found several bright patches of the nebula.

Sources

SDSS-V Local Volume Mapper (LVM): Revealing the Structure of the Rosette Nebula. Villa-Durango et al., Monthly Notices of the Royal Astronomical Society, 2025.
Star Formation in the Rosette Complex. In Handbook of Star Forming Regions, Volume I. Astronomical Society of the Pacific, 2008.
Catalogue of H II Regions. Sharpless, Astrophysical Journal Supplement Series, 1959.
Omega Centauri. European Southern Observatory, 2008.
NGC 2000.0, The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters. Sky Publishing and Cambridge University Press, 1988.
Structural Parameters of Galactic Globular Clusters. H. Baumgardt, University of Queensland.
Measuring the Universe. International Astronomical Union.
Proxima's orbit around Alpha Centauri. Kervella et al., Astronomy & Astrophysics, 2017.
Moon Fact Sheet. NASA, 2024.
Neptune Fact Sheet. NASA, 2024.
Coin Specifications. United States Mint.

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