Located in Cassiopeia, not far from Caldwell 17, Caldwell 18 is a dwarf galaxy and a satellite of the Andromeda galaxy. Also known as NGC 185, it is a member of the Local Group of galaxies. Caldwell 17 is notable for its active galactic nucleus, a region at the center of the galaxy that emits extreme radiation over part of the electromagnetic spectrum.

Some astronomers classify Caldwell 18 as a type II Seyfert galaxy. These types of galaxies appear intensely bright when observed at infrared wavelengths despite their unremarkable brightness in visible wavelengths. Although the classification of Caldwell 18 remains up for debate within the astronomical community, if it is indeed a Seyfert galaxy, then it would be the only one known in the Local Group and the closest one to Earth.

Caldwell 18 was discovered in 1787 by the British astronomer William Herschel (who also discovered the planet Uranus). It is visible from the Northern Hemisphere in the autumn and from northern latitudes of the Southern Hemisphere in the spring. With an apparent magnitude of 9.2, this galaxy can be found with powerful binoculars. Caldwell 18 is easier to spot than the neighboring Caldwell 17, because its center appears more circular and compact than that of its neighbor.

This Hubble image combines observations taken with Hubble’s Wide Field Camera 3 in visible and infrared wavelengths. Clouds of dust appear near the galaxy’s center, and a globular star cluster appears to the left. These Hubble observations helped astronomers study the characteristics of globular clusters in nearby dwarf galaxies.

Credit: NASA, ESA, and A. Ferguson (University of Edinburgh, Institute for Astronomy); Processing: Gladys Kober (NASA/Catholic University of America)