Caldwell 46

This fan-shaped cloud of gas and dust shines by the light of a bright star at the bottom end of the nebula.

Distance

2,500 light-years

Apparent Magnitude

10.0

constellation

Monocerotis

object type

Reflection Nebula

c46
This fan-shaped cloud of gas and dust shines by the light of a bright star at the bottom end of the nebula. The nebula is lit up by the massive, young star dubbed R Monocerotis (R Mon for short). Astronomers believe that dense knots of opaque dust pass close to R Mon and cast moving shadows onto the reflecting dust seen in the rest of the nebula.
NASA/ESA and the Hubble Heritage Team (AURA/STScI)

In this Hubble image of Caldwell 46, a cloud of gas and dust extends from a bright star like smoke rising from a newly lit campfire. The nebula, also cataloged as NGC 2261, is lit up by the massive, young star dubbed R Monocerotis (R Mon for short). Astronomers believe that dense knots of opaque dust pass close to R Mon and cast moving shadows onto the reflecting dust seen in the rest of the nebula.

The nebula’s brightness grows and dims depending on how surrounding dust blocks R Mon, leading this unusual nebula to noticeably change its appearance over the course of just a few weeks. Caldwell 46 is often called Hubble’s Variable Nebula, named after astronomer Edwin P. Hubble, who carried out some of the early studies of this object (and who is also the namesake of the Hubble Space Telescope).

The faint nebula is about one light-year wide and lies approximately 2,500 light-years away from Earth. It was discovered in 1783 by astronomer William Herschel. More than 200 years later, the Hubble telescope’s observations of Caldwell 46 provided astronomers with a new view into the distribution of dust, noting that it forms a thin, shell-like structure around R Mon.

Hubble imaged Caldwell 46 in visible light using the Wide Field and Planetary Camera 2. Seen through the eyepiece of a modest telescope, the approximately magnitude-10 nebula will resemble a soft, triangular puff of smoke. Caldwell 46 is found in the Monoceros (Unicorn) constellation and is best viewed in moonless winter night skies in the Northern Hemisphere, or summer night skies from the Southern Hemisphere.

This Northern Hemisphere star chart shows C46 just below the constellation Monocerotis in the southern part of night sky at 10pm in January.
This star chart for Caldwell 46 represents the view from mid-northern latitudes for the given month and time.
Image courtesy of Stellarium
This Southern Hemisphere star chart shows C46 just below the constellation Monocerotis in the northern part of night sky at 10pm in January.
This star chart for Caldwell 46 represents the view from mid-southern latitudes for the given month and time.
Image courtesy of Stellarium

Glossary

Magnitude - The brightness of an astronomical object, represented by a number; bright objects have low numbers on the magnitude scale, while dim objects have high numbers.

Nebula - An interstellar cloud of dust and gas; either a location where new stars are being forged or a cloud of material ejected into space by a dying star.

Explore Hubble's Caldwell Catalog

The following pages contain some of Hubble’s best images of Caldwell objects.

Stars with four diffraction spikes dot the scene against a black backdrop.

Caldwell 1

Also known as NGC 188, this group of stars formed from a large cloud of gas making the stars roughly…

Red cloud of dust with a bright white star in the center of it. Lots of reddish and orangish stars in the background.

Caldwell 2

This shell of gas is expanding outward, away from the dying star within.

Large grouping of bright white, blue and red stars. Lightly colored blue dust surrounds the stars.

Caldwell 3

This barred spiral galaxy was first spotted by British astronomer William Herschel in April 1793 in the constellation Draco.