How big is Large Magellanic Cloud? | Scale of the Universe

The Large Magellanic Cloud is a small galaxy near the Milky Way, about 160,000 light-years from Earth. A light-year is the distance light travels in one year, about 9.46 trillion kilometers. The galaxy's main body of stars is about 30,000 light-years across. From the Southern Hemisphere it can be seen without a telescope, spanning about 20 times the width of the full Moon.

Size

The Large Magellanic Cloud is an irregular dwarf galaxy: a small galaxy without a neat spiral or oval shape. Like every galaxy, it has no sharp edge, so its width depends on how faint a glow is counted. Galaxy catalogs measure the width out to a standard, very faint level of brightness.

Measured this way, the Updated Nearby Galaxy Catalog, published in 2013, gives the galaxy a width of 10.8 degrees on the sky. At a distance of 160,000 light-years, that angle spans about 30,000 light-years. After correcting for dust in the Milky Way and for the way the galaxy is tilted toward Earth, the catalog lists a width of about 33,000 light-years.

The stars sit inside a halo of thin gas. In 2024, astronomers used the Hubble Space Telescope to measure this halo for the first time. It is about 50,000 light-years across, around one-tenth the size of the gas halos of other galaxies with the same mass.

Size comparisons

The Large Magellanic Cloud is about one-third the width of the Milky Way's disk, which is about 100,000 light-years across.
The Triangulum Galaxy, a spiral galaxy about 60,000 light-years across, is about twice as wide.
Measured the same way in the same catalog, the Large Magellanic Cloud is about three times as wide as the Sagittarius Dwarf Galaxy, which is about 10,000 light-years across.
If the Milky Way's disk were shrunk to the width of a basketball, the Large Magellanic Cloud would be about 7 centimeters (3 inches) across, a little larger than a tennis ball. It would sit about 38 centimeters (15 inches) from Earth's place in the disk.

A close pass by the Milky Way

The Large Magellanic Cloud has about 10 percent of the Milky Way's mass, which makes it heavier than most dwarf galaxies. Many astronomers think it is not in orbit around the Milky Way but passing by, and that it has only recently made its closest approach. It is one of about 50 dwarf galaxies in the Local Group, the family of galaxies that also includes the Milky Way, Andromeda and Triangulum.

Moving through the Milky Way's own halo of gas has stripped away most of the Large Magellanic Cloud's gas halo, which trails behind it like the tail of a comet. What remains is small, but the galaxy has enough mass to hold on to it. That leftover gas allows it to keep forming new stars.

Supernova 1987A

In February 1987, a star in the Large Magellanic Cloud exploded as a supernova, the violent death of a massive star. It was the first supernova visible to the naked eye since 1604. Its light had taken about 160,000 years to reach Earth, so the explosion itself happened about 160,000 years earlier. For several months it shone with the power of 100 million Suns.

About two hours before the light was seen, three observatories detected a burst of neutrinos, tiny particles that barely interact with matter. An explosion like this is expected to leave behind a neutron star, which is the collapsed core of the star, or a black hole. In 2024, the James Webb Space Telescope found the best evidence yet of a neutron star at the site.