The Small Magellanic Cloud is a dwarf galaxy, one of the galaxies that orbit the Milky Way, about 200,000 light-years from Earth. A light-year is the distance light travels in one year, about 9.46 trillion kilometers. Measured out to a standard faint brightness, the galaxy is about 19,000 light-years long. It can be seen with the unaided eye from the Southern Hemisphere.

Size

A galaxy's glow fades gradually toward its edges. To compare galaxies fairly, astronomers often measure each one out to the same very faint brightness. The width measured this way is called D25.

Two major galaxy catalogs, from 1991 and 2003, both give the Small Magellanic Cloud a D25 of 316 arcminutes, about 5.3 degrees of sky. An arcminute is a sixtieth of a degree. The galaxy is narrower in the other direction, 186–234 arcminutes.

Turning an angle on the sky into a true size needs the distance. A 2020 study used eclipsing binaries, pairs of stars that pass in front of each other as they orbit.

It put the galaxy's center 62,440 parsecs away, where a parsec is about 3.26 light-years. That is about 204,000 light-years. At that distance the galaxy is about 5,700 parsecs (19,000 light-years) long and 11,000–14,000 light-years wide.

The galaxy is also deep, stretching far toward and away from Earth. In the same study, the nearest and farthest of the measured stars differed in distance by about 10,000 parsecs (33,000 light-years). The galaxy is stretched out and steeply tilted as seen from Earth.

Size comparisons

• Measured the same way, the Large Magellanic Cloud is about 30,000 light-years long, about 1.6 times the length of its smaller neighbor.
• The disk of the Milky Way, about 100,000 light-years across, is about five times as long as the Small Magellanic Cloud.
• On the sky, the Small Magellanic Cloud is about 10 times as long as the full Moon is wide.
• If the Milky Way's disk were shrunk to the width of a basketball, the Small Magellanic Cloud would be about 4.5 centimeters (1.8 inches) long and about 49 centimeters (19 inches) away.

Known for more than a thousand years

The earliest surviving record of the Magellanic Clouds is in the Book of Fixed Stars, written in 964 by the Persian astronomer Abd al-Rahman al-Sufi. The Small Magellanic Cloud is named after the explorer Ferdinand Magellan. Navigators, Magellan among them, used it to help find their way across the oceans.

A nearby look at the early universe

Astronomers call all elements heavier than hydrogen and helium metals. The Small Magellanic Cloud has less metal than the Milky Way: its stars have about a tenth as much iron, compared with their hydrogen, as the Sun. Its conditions resemble those in galaxies about 2 to 3 billion years after the Big Bang, when the universe was forming stars fastest. That makes it a nearby place to study how stars formed then.

Its most active star-forming region is NGC 346, the only massive cluster in the galaxy still forming stars rapidly. Because dust is made mostly of metals, astronomers expected little of it there. In 2023, however, the James Webb Space Telescope found dust in the disks around young stars in NGC 346, the first time dust had been detected in these particular disks. The team suggested that rocky planets may have formed earlier in the history of the universe than astronomers had thought.

Sources

• Third Reference Catalogue of Bright Galaxies (RC3). de Vaucouleurs et al., Springer-Verlag, via CDS VizieR, 1991.
• HYPERLEDA. I. Identification and designation of galaxies. Paturel et al., Astronomy & Astrophysics, via CDS VizieR, 2003.
• A distance determination to the Small Magellanic Cloud with an accuracy of better than 2 percent based on late-type eclipsing binary stars. Graczyk et al., The Astrophysical Journal, 2020.
• A distance to the Large Magellanic Cloud that is precise to one per cent. Pietrzyński et al., Nature, 2019.
• The observed properties of dwarf galaxies in and around the Local Group. McConnachie, The Astronomical Journal, 2012.
• NGC 602. NASA Chandra X-ray Center, 2013.
• VISTA Peeks Through the Small Magellanic Cloud's Dusty Veil. European Southern Observatory, 2017.
• Webb Uncovers Star Formation in Cluster's Dusty Ribbons. ESA/Webb, 2023.
• Measuring the Universe. International Astronomical Union.
• Our Milky Way Galaxy: How Big is Space?. NASA, 2019.
• Moon Fact Sheet. NASA, 2024.
• Official Basketball Rules 2026: Basketball Equipment. FIBA, 2026.